From patchwork Wed Dec 21 14:23:22 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 635754 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0F3FC4332F for ; Wed, 21 Dec 2022 14:24:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233812AbiLUOYC (ORCPT ); Wed, 21 Dec 2022 09:24:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58338 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233777AbiLUOX6 (ORCPT ); Wed, 21 Dec 2022 09:23:58 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5904D23175; Wed, 21 Dec 2022 06:23:46 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id E6E57B81B99; Wed, 21 Dec 2022 14:23:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 249BDC433F2; Wed, 21 Dec 2022 14:23:42 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="JVpKVwq+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1671632621; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=t6mEMlSUPk+cDhskKS3zWxZg7w+Zno4GCzwlfty+P5I=; b=JVpKVwq++YTiLzAqGC+YEldFExfQkKuiVszXkXyrpDWKn6lFnIctm4stYXXXV6Zzmh1q28 BUEuUl2bjzHSJVRpOK7ZAymOv13wLwhA7YFGwwig3sxZ6TL4mHYPqFlX0AVgn/P+5MmuCv 0RZamVbgGNAM8F/iVx0b1w0voTYXD+M= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id d1900a58 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 21 Dec 2022 14:23:41 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de Cc: "Jason A. Donenfeld" , linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , linux-mm@kvack.org Subject: [PATCH v13 2/7] mm: add VM_DROPPABLE for designating always lazily freeable mappings Date: Wed, 21 Dec 2022 15:23:22 +0100 Message-Id: <20221221142327.126451-3-Jason@zx2c4.com> In-Reply-To: <20221221142327.126451-1-Jason@zx2c4.com> References: <20221221142327.126451-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org The vDSO getrandom() implementation works with a buffer allocated with a new system call that has certain requirements: - It shouldn't be written to core dumps. * Easy: VM_DONTDUMP. - It should be zeroed on fork. * Easy: VM_WIPEONFORK. - It shouldn't be written to swap. * Uh-oh: mlock is rlimited. * Uh-oh: mlock isn't inherited by forks. - It shouldn't reserve actual memory, but it also shouldn't crash when page faulting in memory if none is available * Uh-oh: MAP_NORESERVE respects vm.overcommit_memory=2. * Uh-oh: VM_NORESERVE means segfaults. It turns out that the vDSO getrandom() function has three really nice characteristics that we can exploit to solve this problem: 1) Due to being wiped during fork(), the vDSO code is already robust to having the contents of the pages it reads zeroed out midway through the function's execution. 2) In the absolute worst case of whatever contingency we're coding for, we have the option to fallback to the getrandom() syscall, and everything is fine. 3) The buffers the function uses are only ever useful for a maximum of 60 seconds -- a sort of cache, rather than a long term allocation. These characteristics mean that we can introduce VM_DROPPABLE, which has the following semantics: a) It never is written out to swap. b) Under memory pressure, mm can just drop the pages (so that they're zero when read back again). c) If there's not enough memory to service a page fault, it's not fatal, and no signal is sent. Instead, writes are simply lost. d) It is inherited by fork. e) It doesn't count against the mlock budget, since nothing is locked. This is fairly simple to implement, with the one snag that we have to use 64-bit VM_* flags, but this shouldn't be a problem, since the only consumers will probably be 64-bit anyway. This way, allocations used by vDSO getrandom() can use: VM_DROPPABLE | VM_DONTDUMP | VM_WIPEONFORK | VM_NORESERVE And there will be no problem with OOMing, crashing on overcommitment, using memory when not in use, not wiping on fork(), coredumps, or writing out to swap. At the moment, rather than skipping writes on OOM, the fault handler just returns to userspace, and the instruction is retried. This isn't terrible, but it's not quite what is intended. The actual instruction skipping has to be implemented arch-by-arch, but so does this whole vDSO series, so that's fine. The following commit addresses it for x86. Cc: linux-mm@kvack.org Signed-off-by: Jason A. Donenfeld --- fs/proc/task_mmu.c | 3 +++ include/linux/mm.h | 8 ++++++++ include/trace/events/mmflags.h | 7 +++++++ mm/Kconfig | 3 +++ mm/memory.c | 4 ++++ mm/mempolicy.c | 3 +++ mm/mprotect.c | 2 +- mm/rmap.c | 5 +++-- 8 files changed, 32 insertions(+), 3 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index e35a0398db63..47c7c046f2be 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -711,6 +711,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma) #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR [ilog2(VM_UFFD_MINOR)] = "ui", #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ +#ifdef CONFIG_NEED_VM_DROPPABLE + [ilog2(VM_DROPPABLE)] = "dp", +#endif }; size_t i; diff --git a/include/linux/mm.h b/include/linux/mm.h index f3f196e4d66d..fba3f1e8616b 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -315,11 +315,13 @@ extern unsigned int kobjsize(const void *objp); #define VM_HIGH_ARCH_BIT_2 34 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_BIT_3 35 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_BIT_4 36 /* bit only usable on 64-bit architectures */ +#define VM_HIGH_ARCH_BIT_5 37 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_0 BIT(VM_HIGH_ARCH_BIT_0) #define VM_HIGH_ARCH_1 BIT(VM_HIGH_ARCH_BIT_1) #define VM_HIGH_ARCH_2 BIT(VM_HIGH_ARCH_BIT_2) #define VM_HIGH_ARCH_3 BIT(VM_HIGH_ARCH_BIT_3) #define VM_HIGH_ARCH_4 BIT(VM_HIGH_ARCH_BIT_4) +#define VM_HIGH_ARCH_5 BIT(VM_HIGH_ARCH_BIT_5) #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */ #ifdef CONFIG_ARCH_HAS_PKEYS @@ -335,6 +337,12 @@ extern unsigned int kobjsize(const void *objp); #endif #endif /* CONFIG_ARCH_HAS_PKEYS */ +#ifdef CONFIG_NEED_VM_DROPPABLE +# define VM_DROPPABLE VM_HIGH_ARCH_5 +#else +# define VM_DROPPABLE 0 +#endif + #if defined(CONFIG_X86) # define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */ #elif defined(CONFIG_PPC) diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index 412b5a46374c..82b2fb811d06 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -163,6 +163,12 @@ IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison") # define IF_HAVE_UFFD_MINOR(flag, name) #endif +#ifdef CONFIG_NEED_VM_DROPPABLE +# define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name}, +#else +# define IF_HAVE_VM_DROPPABLE(flag, name) +#endif + #define __def_vmaflag_names \ {VM_READ, "read" }, \ {VM_WRITE, "write" }, \ @@ -195,6 +201,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \ {VM_MIXEDMAP, "mixedmap" }, \ {VM_HUGEPAGE, "hugepage" }, \ {VM_NOHUGEPAGE, "nohugepage" }, \ +IF_HAVE_VM_DROPPABLE(VM_DROPPABLE, "droppable" ) \ {VM_MERGEABLE, "mergeable" } \ #define show_vma_flags(flags) \ diff --git a/mm/Kconfig b/mm/Kconfig index ff7b209dec05..91fd0be96ca4 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1030,6 +1030,9 @@ config ARCH_USES_HIGH_VMA_FLAGS bool config ARCH_HAS_PKEYS bool +config NEED_VM_DROPPABLE + select ARCH_USES_HIGH_VMA_FLAGS + bool config ARCH_USES_PG_ARCH_X bool diff --git a/mm/memory.c b/mm/memory.c index aad226daf41b..1ade407ccbf9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5220,6 +5220,10 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, lru_gen_exit_fault(); + /* If the mapping is droppable, then errors due to OOM aren't fatal. */ + if (vma->vm_flags & VM_DROPPABLE) + ret &= ~VM_FAULT_OOM; + if (flags & FAULT_FLAG_USER) { mem_cgroup_exit_user_fault(); /* diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 61aa9aedb728..5aeb85bc9627 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2172,6 +2172,9 @@ struct folio *vma_alloc_folio(gfp_t gfp, int order, struct vm_area_struct *vma, int preferred_nid; nodemask_t *nmask; + if (vma->vm_flags & VM_DROPPABLE) + gfp |= __GFP_NOWARN | __GFP_NORETRY; + pol = get_vma_policy(vma, addr); if (pol->mode == MPOL_INTERLEAVE) { diff --git a/mm/mprotect.c b/mm/mprotect.c index 908df12caa26..a679cc5d1c75 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -593,7 +593,7 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma, may_expand_vm(mm, oldflags, nrpages)) return -ENOMEM; if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB| - VM_SHARED|VM_NORESERVE))) { + VM_SHARED|VM_NORESERVE|VM_DROPPABLE))) { charged = nrpages; if (security_vm_enough_memory_mm(mm, charged)) return -ENOMEM; diff --git a/mm/rmap.c b/mm/rmap.c index b616870a09be..5ed46e59dfcd 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1294,7 +1294,8 @@ void page_add_new_anon_rmap(struct page *page, int nr; VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma); - __SetPageSwapBacked(page); + if (!(vma->vm_flags & VM_DROPPABLE)) + __SetPageSwapBacked(page); if (likely(!PageCompound(page))) { /* increment count (starts at -1) */ @@ -1683,7 +1684,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * plus the rmap(s) (dropped by discard:). */ if (ref_count == 1 + map_count && - !folio_test_dirty(folio)) { + (!folio_test_dirty(folio) || (vma->vm_flags & VM_DROPPABLE))) { /* Invalidate as we cleared the pte */ mmu_notifier_invalidate_range(mm, address, address + PAGE_SIZE); From patchwork Wed Dec 21 14:23:24 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 635753 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD570C4167B for ; Wed, 21 Dec 2022 14:24:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234436AbiLUOYP (ORCPT ); Wed, 21 Dec 2022 09:24:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58388 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234094AbiLUOYA (ORCPT ); Wed, 21 Dec 2022 09:24:00 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D0BF623BC4; Wed, 21 Dec 2022 06:23:52 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6A491B81B9A; Wed, 21 Dec 2022 14:23:51 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ACC3EC433D2; Wed, 21 Dec 2022 14:23:48 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="Xxu/rfPc" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1671632627; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EPbPp9pVXfRIMWZXHVXc8hFjwDXo0mRk/v2R9kWPrps=; b=Xxu/rfPc2TkClk7VMRECuFIDnfzQuF4IfmPbQeAal5dzL+jOc3uwqmmBinbP1xtts1lupv b5Nx1ouEdJvATdaTWWrBkP6PQBxi9paQq79HuweLOF+vqcerJHk7N4D3kLPJZxoP0WPplu djDYawMDDoGcgzVh8vBnWNjfi5T/gGU= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 6b20001a (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 21 Dec 2022 14:23:47 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de Cc: "Jason A. Donenfeld" , linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner Subject: [PATCH v13 4/7] random: add vgetrandom_alloc() syscall Date: Wed, 21 Dec 2022 15:23:24 +0100 Message-Id: <20221221142327.126451-5-Jason@zx2c4.com> In-Reply-To: <20221221142327.126451-1-Jason@zx2c4.com> References: <20221221142327.126451-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org The vDSO getrandom() works over an opaque per-thread state of an unexported size, which must be marked VM_WIPEONFORK, VM_DONTDUMP, VM_NORESERVE, and VM_DROPPABLE for proper operation. Over time, the nuances of these allocations may change or grow or even differ based on architectural features. The syscall has the signature: void *vgetrandom_alloc(unsigned int *num, unsigned int *size_per_each, unsigned long addr, unsigned int flags); This takes a hinted number of opaque states in `num`, and returns a pointer to an array of opaque states, the number actually allocated back in `num`, and the size in bytes of each one in `size_per_each`, enabling a libc to slice up the returned array into a state per each thread, while ensuring that no single state straddles a page boundary. (The `flags` and `addr` arguments, as well as the `*size_per_each` input value, are reserved for the future and are forced to be zero zero for now.) Libc is expected to allocate a chunk of these on first use, and then dole them out to threads as they're created, allocating more when needed. The returned address of the first state may be passed to munmap(2) with a length of `num * size_per_each`, in order to deallocate the memory. We very intentionally do *not* leave state allocation for vDSO getrandom() up to userspace itself, but rather provide this new syscall for such allocations. vDSO getrandom() must not store its state in just any old memory address, but rather just ones that the kernel specially allocates for it, leaving the particularities of those allocations up to the kernel. The allocation of states is intended to be integrated into libc's thread management. As an illustrative example, the following code might be used to do the same outside of libc. Though, vgetrandom_alloc() is not expected to be exposed outside of libc, and the pthread usage here is expected to be elided into libc internals. This allocation scheme is very naive and does not shrink; other implementations may choose to be more complex. static void *vgetrandom_alloc(unsigned int *num, unsigned int *size_per_each) { *size_per_each = 0; /* Must be zero on input. */ return (void *)syscall(__NR_vgetrandom_alloc, &num, &size_per_each, 0 /* reserved @addr */, 0 /* reserved @flags */); } static struct { pthread_mutex_t lock; void **states; size_t len, cap; } grnd_allocator = { .lock = PTHREAD_MUTEX_INITIALIZER }; static void *vgetrandom_get_state(void) { void *state = NULL; pthread_mutex_lock(&grnd_allocator.lock); if (!grnd_allocator.len) { size_t new_cap; size_t page_size = getpagesize(); unsigned int num = sysconf(_SC_NPROCESSORS_ONLN); /* Could be arbitrary, just a hint. */ unsigned int size_per_each; void *new_block = vgetrandom_alloc(&num, &size_per_each); void *new_states; if (new_block == MAP_FAILED) goto out; new_cap = grnd_allocator.cap + num; new_states = reallocarray(grnd_allocator.states, new_cap, sizeof(*grnd_allocator.states)); if (!new_states) { munmap(new_block, num * size_per_each); goto out; } grnd_allocator.cap = new_cap; grnd_allocator.states = new_states; for (size_t i = 0; i < num; ++i) { grnd_allocator.states[i] = new_block; if (((uintptr_t)new_block & (page_size - 1)) + size_per_each > page_size) new_block = (void *)(((uintptr_t)new_block + page_size) & (page_size - 1)); else new_block += size_per_each; } grnd_allocator.len = num; } state = grnd_allocator.states[--grnd_allocator.len]; out: pthread_mutex_unlock(&grnd_allocator.lock); return state; } static void vgetrandom_put_state(void *state) { if (!state) return; pthread_mutex_lock(&grnd_allocator.lock); grnd_allocator.states[grnd_allocator.len++] = state; pthread_mutex_unlock(&grnd_allocator.lock); } Signed-off-by: Jason A. Donenfeld --- MAINTAINERS | 1 + drivers/char/random.c | 136 +++++++++++++++++++++++++++++++++++++++ include/linux/syscalls.h | 3 + include/vdso/getrandom.h | 16 +++++ kernel/sys_ni.c | 3 + lib/vdso/Kconfig | 6 ++ 6 files changed, 165 insertions(+) create mode 100644 include/vdso/getrandom.h diff --git a/MAINTAINERS b/MAINTAINERS index 5490b1f94803..1984d383aebf 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17517,6 +17517,7 @@ T: git https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git S: Maintained F: drivers/char/random.c F: drivers/virt/vmgenid.c +F: include/vdso/getrandom.h RAPIDIO SUBSYSTEM M: Matt Porter diff --git a/drivers/char/random.c b/drivers/char/random.c index ce3ccd172cc8..6425f5f838e0 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -8,6 +8,7 @@ * into roughly six sections, each with a section header: * * - Initialization and readiness waiting. + * - vDSO support helpers. * - Fast key erasure RNG, the "crng". * - Entropy accumulation and extraction routines. * - Entropy collection routines. @@ -39,6 +40,7 @@ #include #include #include +#include #include #include #include @@ -56,6 +58,9 @@ #include #include #include +#ifdef CONFIG_VDSO_GETRANDOM +#include +#endif #include #include #include @@ -169,6 +174,137 @@ int __cold execute_with_initialized_rng(struct notifier_block *nb) __func__, (void *)_RET_IP_, crng_init) + +/******************************************************************** + * + * vDSO support helpers. + * + * The actual vDSO function is defined over in lib/vdso/getrandom.c, + * but this section contains the kernel-mode helpers to support that. + * + ********************************************************************/ + +#ifdef CONFIG_VDSO_GETRANDOM +/** + * sys_vgetrandom_alloc - Allocate opaque states for use with vDSO getrandom(). + * + * @num: On input, a pointer to a suggested hint of how many states to + * allocate, and on return the number of states actually allocated. + * + * @size_per_each: On input, must be zero. On return, the size of each state allocated, + * so that the caller can split up the returned allocation into + * individual states. + * + * @addr: Reserved, must be zero. + * + * @flags: Reserved, must be zero. + * + * The getrandom() vDSO function in userspace requires an opaque state, which + * this function allocates by mapping a certain number of special pages into + * the calling process. It takes a hint as to the number of opaque states + * desired, and provides the caller with the number of opaque states actually + * allocated, the size of each one in bytes, and the address of the first + * state, which may be split up into @num states of @size_per_each bytes each, + * by adding @size_per_each to the returned first state @num times, while + * ensuring that no single state straddles a page boundary. + * + * Returns the address of the first state in the allocation on success, or a + * negative error value on failure. + * + * The returned address of the first state may be passed to munmap(2) with a + * length of `(size_t)num * (size_t)size_per_each`, in order to deallocate the + * memory, after which it is invalid to pass it to vDSO getrandom(). + * + * States allocated by this function must not be dereferenced, written, read, + * or otherwise manipulated. The *only* supported operations are: + * - Splitting up the states in intervals of @size_per_each, no more than + * @num times from the first state, while ensuring that no single state + * straddles a page boundary. + * - Passing a state to the getrandom() vDSO function's @opaque_state + * parameter, but not passing the same state at the same time to two such + * calls. + * - Passing the first state and the total length to munmap(2), as described + * above. + * All other uses are undefined behavior, which is subject to change or removal. + */ +SYSCALL_DEFINE4(vgetrandom_alloc, unsigned int __user *, num, + unsigned int __user *, size_per_each, unsigned long, addr, + unsigned int, flags) +{ + struct mm_struct *mm = current->mm; + size_t state_size, alloc_size, num_states; + unsigned long pages_addr, populate, mm_flags; + unsigned int num_hint; + int ret; + + /* + * @flags and @addr are currently unused, so in order to reserve them + * for the future, force them to be set to zero by current callers. + */ + if (flags || addr) + return -EINVAL; + + /* + * Also enforce that *size_per_each is zero on input, in case this becomes + * useful later on. + */ + if (get_user(num_hint, size_per_each)) + return -EFAULT; + if (num_hint) + return -EINVAL; + + if (get_user(num_hint, num)) + return -EFAULT; + + state_size = sizeof(struct vgetrandom_state); + num_states = clamp_t(size_t, num_hint, 1, (SIZE_MAX & PAGE_MASK) / state_size); + alloc_size = PAGE_ALIGN(num_states * state_size); + /* + * States cannot straddle page boundaries, so calculate the number of + * states that can fit inside of a page without being split, and then + * multiply that out by the number of pages allocated. + */ + num_states = (PAGE_SIZE / state_size) * (alloc_size / PAGE_SIZE); + + if (mmap_write_lock_killable(mm)) + return -EINTR; + mm_flags = mm->def_flags; + + mm->def_flags |= + /* + * Don't allow state to be written to swap, to preserve forward secrecy. + * But also don't mlock it or pre-reserve it, and allow it to + * be discarded under memory pressure. If no memory is available, returns + * zeros rather than segfaulting. + */ + VM_DROPPABLE | VM_NORESERVE | + + /* Don't allow the state to survive forks, to prevent random number re-use. */ + VM_WIPEONFORK | + + /* Don't write random state into coredumps. */ + VM_DONTDUMP; + + pages_addr = do_mmap(NULL, 0, alloc_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, 0, &populate, NULL); + + mm->def_flags = mm_flags; + mmap_write_unlock(mm); + if (IS_ERR_VALUE(pages_addr)) + return pages_addr; + + ret = -EFAULT; + if (put_user(num_states, num) || put_user(state_size, size_per_each)) + goto err_unmap; + + return pages_addr; + +err_unmap: + vm_munmap(pages_addr, alloc_size); + return ret; +} +#endif + /********************************************************************* * * Fast key erasure RNG, the "crng". diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 33a0ee3bcb2e..00f2b590b834 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -1008,6 +1008,9 @@ asmlinkage long sys_seccomp(unsigned int op, unsigned int flags, void __user *uargs); asmlinkage long sys_getrandom(char __user *buf, size_t count, unsigned int flags); +asmlinkage long sys_vgetrandom_alloc(unsigned int __user *num, + unsigned int __user *size_per_each, + unsigned long addr, unsigned int flags); asmlinkage long sys_memfd_create(const char __user *uname_ptr, unsigned int flags); asmlinkage long sys_bpf(int cmd, union bpf_attr *attr, unsigned int size); asmlinkage long sys_execveat(int dfd, const char __user *filename, diff --git a/include/vdso/getrandom.h b/include/vdso/getrandom.h new file mode 100644 index 000000000000..e3ceb1976386 --- /dev/null +++ b/include/vdso/getrandom.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2022 Jason A. Donenfeld . All Rights Reserved. + */ + +#ifndef _VDSO_GETRANDOM_H +#define _VDSO_GETRANDOM_H + +/** + * struct vgetrandom_state - State used by vDSO getrandom() and allocated by vgetrandom_alloc(). + * + * Currently empty, as the vDSO getrandom() function has not yet been implemented. + */ +struct vgetrandom_state { int placeholder; }; + +#endif /* _VDSO_GETRANDOM_H */ diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 860b2dcf3ac4..f28196cb919b 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -360,6 +360,9 @@ COND_SYSCALL(pkey_free); /* memfd_secret */ COND_SYSCALL(memfd_secret); +/* random */ +COND_SYSCALL(vgetrandom_alloc); + /* * Architecture specific weak syscall entries. */ diff --git a/lib/vdso/Kconfig b/lib/vdso/Kconfig index d883ac299508..f88580960182 100644 --- a/lib/vdso/Kconfig +++ b/lib/vdso/Kconfig @@ -31,3 +31,9 @@ config GENERIC_VDSO_TIME_NS VDSO endif + +config VDSO_GETRANDOM + bool + select NEED_VM_DROPPABLE + help + Selected by architectures that support vDSO getrandom(). From patchwork Wed Dec 21 14:23:26 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 635752 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CDA86C4167B for ; Wed, 21 Dec 2022 14:24:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234487AbiLUOYz (ORCPT ); Wed, 21 Dec 2022 09:24:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234010AbiLUOYL (ORCPT ); Wed, 21 Dec 2022 09:24:11 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB71223BD6; Wed, 21 Dec 2022 06:23:57 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1C5F1617E4; Wed, 21 Dec 2022 14:23:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 23225C433F0; Wed, 21 Dec 2022 14:23:55 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="H2Bn34hJ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1671632634; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9+eBAmbpbdea8DaiBsQ0U/ZmfhFOLmnWTai6jkJI6wk=; b=H2Bn34hJ8YPNy/uqrSdCtLCNqFAFhlK0ZhjXjDgqda8Vv+CYfoU2SDFlnaRgzeBTV9lcBh /q7PEDaITuqEdy5W2CAtOLsv5AntMge6lO7g0WnTtXsp7eacXyy7JUOgQj3yqePTJ6OSb8 fXe1biRzlCOgeQ/nIepmP8RKrA2Ll48= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 0962b29f (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 21 Dec 2022 14:23:54 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de Cc: "Jason A. Donenfeld" , linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner Subject: [PATCH v13 6/7] random: introduce generic vDSO getrandom() implementation Date: Wed, 21 Dec 2022 15:23:26 +0100 Message-Id: <20221221142327.126451-7-Jason@zx2c4.com> In-Reply-To: <20221221142327.126451-1-Jason@zx2c4.com> References: <20221221142327.126451-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org Provide a generic C vDSO getrandom() implementation, which operates on an opaque state returned by vgetrandom_alloc() and produces random bytes the same way as getrandom(). This has a the API signature: ssize_t vgetrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state); The return value and the first 3 arguments are the same as ordinary getrandom(), while the last argument is a pointer to the opaque allocated state. Were all four arguments passed to the getrandom() syscall, nothing different would happen, and the functions would have the exact same behavior. The actual vDSO RNG algorithm implemented is the same one implemented by drivers/char/random.c, using the same fast-erasure techniques as that. Should the in-kernel implementation change, so too will the vDSO one. It requires an implementation of ChaCha20 that does not use any stack, in order to maintain forward secrecy if a multi-threaded program forks (though this does not account for a similar issue with SA_SIGINFO copying registers to the stack), so this is left as an architecture-specific fill-in. Stack-less ChaCha20 is an easy algorithm to implement on a variety of architectures, so this shouldn't be too onerous. Initially, the state is keyless, and so the first call makes a getrandom() syscall to generate that key, and then uses it for subsequent calls. By keeping track of a generation counter, it knows when its key is invalidated and it should fetch a new one using the syscall. Later, more than just a generation counter might be used. Since MADV_WIPEONFORK is set on the opaque state, the key and related state is wiped during a fork(), so secrets don't roll over into new processes, and the same state doesn't accidentally generate the same random stream. The generation counter, as well, is always >0, so that the 0 counter is a useful indication of a fork() or otherwise uninitialized state. If the kernel RNG is not yet initialized, then the vDSO always calls the syscall, because that behavior cannot be emulated in userspace, but fortunately that state is short lived and only during early boot. If it has been initialized, then there is no need to inspect the `flags` argument, because the behavior does not change post-initialization regardless of the `flags` value. Since the opaque state passed to it is mutated, vDSO getrandom() is not reentrant, when used with the same opaque state, which libc should be mindful of. vgetrandom_alloc() and vDSO getrandom() provide the ability for userspace to generate random bytes quickly and safely, and are intended to be integrated into libc's thread management. As an illustrative example, together with the example code from "random: add vgetrandom_alloc() syscall", the following code might be used to do the same outside of libc. In a libc, only the non-static vgetrandom() function at the end would be exported as part of a getrandom() implementations, and the various pthread-isms are expected to be elided into libc internals. static struct { ssize_t(*fn)(void *buf, size_t len, unsigned long flags, void *state); pthread_key_t key; pthread_once_t initialized; } grnd_ctx = { .initialized = PTHREAD_ONCE_INIT }; static void vgetrandom_init(void) { if (pthread_key_create(&grnd_ctx.key, vgetrandom_put_state) != 0) return; grnd_ctx.fn = vdso_sym("LINUX_2.6", "__vdso_getrandom"); } ssize_t vgetrandom(void *buf, size_t len, unsigned long flags) { void *state; pthread_once(&grnd_ctx.initialized, vgetrandom_init); if (!grnd_ctx.fn) return getrandom(buf, len, flags); state = pthread_getspecific(grnd_ctx.key); if (!state) { state = vgetrandom_get_state(); if (pthread_setspecific(grnd_ctx.key, state) != 0) { vgetrandom_put_state(state); state = NULL; } if (!state) return getrandom(buf, len, flags); } return grnd_ctx.fn(buf, len, flags, state); } Signed-off-by: Jason A. Donenfeld --- MAINTAINERS | 1 + drivers/char/random.c | 7 + include/vdso/datapage.h | 12 + include/vdso/getrandom.h | 32 +- include/vdso/types.h | 35 +++ lib/vdso/getrandom.c | 224 ++++++++++++++ tools/testing/selftests/vDSO/.gitignore | 1 + tools/testing/selftests/vDSO/Makefile | 2 + .../selftests/vDSO/vdso_test_getrandom.c | 283 ++++++++++++++++++ 9 files changed, 595 insertions(+), 2 deletions(-) create mode 100644 include/vdso/types.h create mode 100644 lib/vdso/getrandom.c create mode 100644 tools/testing/selftests/vDSO/vdso_test_getrandom.c diff --git a/MAINTAINERS b/MAINTAINERS index 1984d383aebf..6dfb8ebee747 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17518,6 +17518,7 @@ S: Maintained F: drivers/char/random.c F: drivers/virt/vmgenid.c F: include/vdso/getrandom.h +F: lib/vdso/getrandom.c RAPIDIO SUBSYSTEM M: Matt Porter diff --git a/drivers/char/random.c b/drivers/char/random.c index 6425f5f838e0..660cd15b6228 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -60,6 +60,7 @@ #include #ifdef CONFIG_VDSO_GETRANDOM #include +#include #endif #include #include @@ -407,6 +408,9 @@ static void crng_reseed(struct work_struct *work) if (next_gen == ULONG_MAX) ++next_gen; WRITE_ONCE(base_crng.generation, next_gen); +#ifdef CONFIG_VDSO_GETRANDOM + smp_store_release(&_vdso_rng_data.generation, next_gen + 1); +#endif if (!static_branch_likely(&crng_is_ready)) crng_init = CRNG_READY; spin_unlock_irqrestore(&base_crng.lock, flags); @@ -857,6 +861,9 @@ static void __cold _credit_init_bits(size_t bits) if (static_key_initialized) execute_in_process_context(crng_set_ready, &set_ready); atomic_notifier_call_chain(&random_ready_notifier, 0, NULL); +#ifdef CONFIG_VDSO_GETRANDOM + smp_store_release(&_vdso_rng_data.is_ready, true); +#endif wake_up_interruptible(&crng_init_wait); kill_fasync(&fasync, SIGIO, POLL_IN); pr_notice("crng init done\n"); diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h index 73eb622e7663..d1f800c1c718 100644 --- a/include/vdso/datapage.h +++ b/include/vdso/datapage.h @@ -18,6 +18,7 @@ #include #include #include +#include #ifdef CONFIG_ARCH_HAS_VDSO_DATA #include @@ -109,6 +110,16 @@ struct vdso_data { struct arch_vdso_data arch_data; }; +/** + * struct vdso_rng_data - vdso RNG state information + * @generation: counter representing the number of RNG reseeds + * @is_ready: boolean signaling whether the RNG is initialized + */ +struct vdso_rng_data { + vdso_kernel_ulong generation; + u8 is_ready; +}; + /* * We use the hidden visibility to prevent the compiler from generating a GOT * relocation. Not only is going through a GOT useless (the entry couldn't and @@ -120,6 +131,7 @@ struct vdso_data { */ extern struct vdso_data _vdso_data[CS_BASES] __attribute__((visibility("hidden"))); extern struct vdso_data _timens_data[CS_BASES] __attribute__((visibility("hidden"))); +extern struct vdso_rng_data _vdso_rng_data __attribute__((visibility("hidden"))); /* * The generic vDSO implementation requires that gettimeofday.h diff --git a/include/vdso/getrandom.h b/include/vdso/getrandom.h index e3ceb1976386..7dc93d5f72dc 100644 --- a/include/vdso/getrandom.h +++ b/include/vdso/getrandom.h @@ -6,11 +6,39 @@ #ifndef _VDSO_GETRANDOM_H #define _VDSO_GETRANDOM_H +#include +#include + /** * struct vgetrandom_state - State used by vDSO getrandom() and allocated by vgetrandom_alloc(). * - * Currently empty, as the vDSO getrandom() function has not yet been implemented. + * @batch: One and a half ChaCha20 blocks of buffered RNG output. + * + * @key: Key to be used for generating next batch. + * + * @batch_key: Union of the prior two members, which is exactly two full + * ChaCha20 blocks in size, so that @batch and @key can be filled + * together. + * + * @generation: Snapshot of @rng_info->generation in the vDSO data page at + * the time @key was generated. + * + * @pos: Offset into @batch of the next available random byte. + * + * @in_use: Reentrancy guard for reusing a state within the same thread + * due to signal handlers. */ -struct vgetrandom_state { int placeholder; }; +struct vgetrandom_state { + union { + struct { + u8 batch[CHACHA_BLOCK_SIZE * 3 / 2]; + u32 key[CHACHA_KEY_SIZE / sizeof(u32)]; + }; + u8 batch_key[CHACHA_BLOCK_SIZE * 2]; + }; + vdso_kernel_ulong generation; + u8 pos; + bool in_use; +}; #endif /* _VDSO_GETRANDOM_H */ diff --git a/include/vdso/types.h b/include/vdso/types.h new file mode 100644 index 000000000000..ce131463aeff --- /dev/null +++ b/include/vdso/types.h @@ -0,0 +1,35 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2022 Jason A. Donenfeld . All Rights Reserved. + */ +#ifndef __VDSO_TYPES_H +#define __VDSO_TYPES_H + +#include + +/** + * type vdso_kernel_ulong - unsigned long type that matches kernel's unsigned long + * + * Data shared between userspace and the kernel must operate the same way in both 64-bit code and in + * 32-bit compat code, over the same potentially 64-bit kernel. This type represents the size of an + * unsigned long as used by kernel code. This isn't necessarily the same as an unsigned long as used + * by userspace, however. + * + * +-------------------+-------------------+------------------+-------------------+ + * | 32-bit userspace | 32-bit userspace | 64-bit userspace | 64-bit userspace | + * | unsigned long | vdso_kernel_ulong | unsigned long | vdso_kernel_ulong | + * +---------------+-------------------+-------------------+------------------+-------------------+ + * | 32-bit kernel | ✓ same size | ✓ same size | + * | unsigned long | | | + * +---------------+-------------------+-------------------+------------------+-------------------+ + * | 64-bit kernel | ✘ different size! | ✓ same size | ✓ same size | ✓ same size | + * | unsigned long | | | | | + * +---------------+-------------------+-------------------+------------------+-------------------+ + */ +#ifdef CONFIG_64BIT +typedef u64 vdso_kernel_ulong; +#else +typedef u32 vdso_kernel_ulong; +#endif + +#endif /* __VDSO_TYPES_H */ diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c new file mode 100644 index 000000000000..64ab28913a23 --- /dev/null +++ b/lib/vdso/getrandom.c @@ -0,0 +1,224 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2022 Jason A. Donenfeld . All Rights Reserved. + */ + +#include +#include +#include +#include +#include +#include +#include + +#define MEMCPY_AND_ZERO_SRC(type, dst, src, len) do { \ + while (len >= sizeof(type)) { \ + __put_unaligned_t(type, __get_unaligned_t(type, src), dst); \ + __put_unaligned_t(type, 0, src); \ + dst += sizeof(type); \ + src += sizeof(type); \ + len -= sizeof(type); \ + } \ +} while (0) + +static void memcpy_and_zero_src(void *dst, void *src, size_t len) +{ + if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) { + if (IS_ENABLED(CONFIG_64BIT)) + MEMCPY_AND_ZERO_SRC(u64, dst, src, len); + MEMCPY_AND_ZERO_SRC(u32, dst, src, len); + MEMCPY_AND_ZERO_SRC(u16, dst, src, len); + } + MEMCPY_AND_ZERO_SRC(u8, dst, src, len); +} + +/** + * __cvdso_getrandom_data - Generic vDSO implementation of getrandom() syscall. + * @rng_info: Describes state of kernel RNG, memory shared with kernel. + * @buffer: Destination buffer to fill with random bytes. + * @len: Size of @buffer in bytes. + * @flags: Zero or more GRND_* flags. + * @opaque_state: Pointer to an opaque state area. + * + * This implements a "fast key erasure" RNG using ChaCha20, in the same way that the kernel's + * getrandom() syscall does. It periodically reseeds its key from the kernel's RNG, at the same + * schedule that the kernel's RNG is reseeded. If the kernel's RNG is not ready, then this always + * calls into the syscall. + * + * @opaque_state *must* be allocated using the vgetrandom_alloc() syscall. Unless external locking + * is used, one state must be allocated per thread, as it is not safe to call this function + * concurrently with the same @opaque_state. However, it is safe to call this using the same + * @opaque_state that is shared between main code and signal handling code, within the same thread. + * + * Returns the number of random bytes written to @buffer, or a negative value indicating an error. + */ +static __always_inline ssize_t +__cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_t len, + unsigned int flags, void *opaque_state) +{ + ssize_t ret = min_t(size_t, INT_MAX & PAGE_MASK /* = MAX_RW_COUNT */, len); + struct vgetrandom_state *state = opaque_state; + size_t batch_len, nblocks, orig_len = len; + unsigned long current_generation; + void *orig_buffer = buffer; + u32 counter[2] = { 0 }; + bool in_use, have_retried = false; + + /* The state must not straddle a page, since pages can be zeroed at any time. */ + if (unlikely(((unsigned long)opaque_state & ~PAGE_MASK) + sizeof(*state) > PAGE_SIZE)) + goto fallback_syscall; + + /* + * If the kernel's RNG is not yet ready, then it's not possible to provide random bytes from + * userspace, because A) the various @flags require this to block, or not, depending on + * various factors unavailable to userspace, and B) the kernel's behavior before the RNG is + * ready is to reseed from the entropy pool at every invocation. + */ + if (unlikely(!READ_ONCE(rng_info->is_ready))) + goto fallback_syscall; + + /* + * This condition is checked after @rng_info->is_ready, because before the kernel's RNG is + * initialized, the @flags parameter may require this to block or return an error, even when + * len is zero. + */ + if (unlikely(!len)) + return 0; + + /* + * @state->in_use is basic reentrancy protection against this running in a signal handler + * with the same @opaque_state, but obviously not atomic wrt multiple CPUs or more than one + * level of reentrancy. If a signal interrupts this after reading @state->in_use, but before + * writing @state->in_use, there is still no race, because the signal handler will run to + * its completion before returning execution. + */ + in_use = READ_ONCE(state->in_use); + if (unlikely(in_use)) + goto fallback_syscall; + WRITE_ONCE(state->in_use, true); + +retry_generation: + /* + * @rng_info->generation must always be read here, as it serializes @state->key with the + * kernel's RNG reseeding schedule. + */ + current_generation = READ_ONCE(rng_info->generation); + + /* + * If @state->generation doesn't match the kernel RNG's generation, then it means the + * kernel's RNG has reseeded, and so @state->key is reseeded as well. + */ + if (unlikely(state->generation != current_generation)) { + /* + * Write the generation before filling the key, in case of fork. If there is a fork + * just after this line, the two forks will get different random bytes from the + * syscall, which is good. However, were this line to occur after the getrandom + * syscall, then both child and parent could have the same bytes and the same + * generation counter, so the fork would not be detected. Therefore, write + * @state->generation before the call to the getrandom syscall. + */ + WRITE_ONCE(state->generation, current_generation); + + /* Prevent the syscall from being reordered wrt current_generation. */ + barrier(); + + /* Reseed @state->key using fresh bytes from the kernel. */ + if (getrandom_syscall(state->key, sizeof(state->key), 0) != sizeof(state->key)) { + /* + * If the syscall failed to refresh the key, then @state->key is now + * invalid, so invalidate the generation so that it is not used again, and + * fallback to using the syscall entirely. + */ + WRITE_ONCE(state->generation, 0); + + /* + * Set @state->in_use to false only after the last write to @state in the + * line above. + */ + WRITE_ONCE(state->in_use, false); + + goto fallback_syscall; + } + + /* + * Set @state->pos to beyond the end of the batch, so that the batch is refilled + * using the new key. + */ + state->pos = sizeof(state->batch); + } + + /* Set len to the total amount of bytes that this function is allowed to read, ret. */ + len = ret; +more_batch: + /* + * First use bytes out of @state->batch, which may have been filled by the last call to this + * function. + */ + batch_len = min_t(size_t, sizeof(state->batch) - state->pos, len); + if (batch_len) { + /* Zeroing at the same time as memcpying helps preserve forward secrecy. */ + memcpy_and_zero_src(buffer, state->batch + state->pos, batch_len); + state->pos += batch_len; + buffer += batch_len; + len -= batch_len; + } + + if (!len) { + /* Prevent the loop from being reordered wrt ->generation. */ + barrier(); + + /* + * Since @rng_info->generation will never be 0, re-read @state->generation, rather + * than using the local current_generation variable, to learn whether a fork + * occurred or if @state was zeroed due to memory pressure. Primarily, though, this + * indicates whether the kernel's RNG has reseeded, in which case generate a new key + * and start over. + */ + if (unlikely(READ_ONCE(state->generation) != READ_ONCE(rng_info->generation))) { + /* + * Prevent this from looping forever in case of low memory or racing with a + * user force-reseeding the kernel's RNG using the ioctl. + */ + if (have_retried) + goto fallback_syscall; + + have_retried = true; + buffer = orig_buffer; + goto retry_generation; + } + + /* + * Set @state->in_use to false only when there will be no more reads or writes of + * @state. + */ + WRITE_ONCE(state->in_use, false); + return ret; + } + + /* Generate blocks of RNG output directly into @buffer while there's enough room left. */ + nblocks = len / CHACHA_BLOCK_SIZE; + if (nblocks) { + __arch_chacha20_blocks_nostack(buffer, state->key, counter, nblocks); + buffer += nblocks * CHACHA_BLOCK_SIZE; + len -= nblocks * CHACHA_BLOCK_SIZE; + } + + BUILD_BUG_ON(sizeof(state->batch_key) % CHACHA_BLOCK_SIZE != 0); + + /* Refill the batch and then overwrite the key, in order to preserve forward secrecy. */ + __arch_chacha20_blocks_nostack(state->batch_key, state->key, counter, + sizeof(state->batch_key) / CHACHA_BLOCK_SIZE); + + /* Since the batch was just refilled, set the position back to 0 to indicate a full batch. */ + state->pos = 0; + goto more_batch; + +fallback_syscall: + return getrandom_syscall(orig_buffer, orig_len, flags); +} + +static __always_inline ssize_t +__cvdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state) +{ + return __cvdso_getrandom_data(__arch_get_vdso_rng_data(), buffer, len, flags, opaque_state); +} diff --git a/tools/testing/selftests/vDSO/.gitignore b/tools/testing/selftests/vDSO/.gitignore index a8dc51af5a9c..7dbfdec53f3d 100644 --- a/tools/testing/selftests/vDSO/.gitignore +++ b/tools/testing/selftests/vDSO/.gitignore @@ -6,3 +6,4 @@ vdso_test_correctness vdso_test_gettimeofday vdso_test_getcpu vdso_standalone_test_x86 +vdso_test_getrandom diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile index d53a4d8008f9..a33b4d200a32 100644 --- a/tools/testing/selftests/vDSO/Makefile +++ b/tools/testing/selftests/vDSO/Makefile @@ -11,6 +11,7 @@ ifeq ($(ARCH),$(filter $(ARCH),x86 x86_64)) TEST_GEN_PROGS += $(OUTPUT)/vdso_standalone_test_x86 endif TEST_GEN_PROGS += $(OUTPUT)/vdso_test_correctness +TEST_GEN_PROGS += $(OUTPUT)/vdso_test_getrandom CFLAGS := -std=gnu99 CFLAGS_vdso_standalone_test_x86 := -nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector @@ -33,3 +34,4 @@ $(OUTPUT)/vdso_test_correctness: vdso_test_correctness.c vdso_test_correctness.c \ -o $@ \ $(LDFLAGS_vdso_test_correctness) +$(OUTPUT)/vdso_test_getrandom: parse_vdso.c diff --git a/tools/testing/selftests/vDSO/vdso_test_getrandom.c b/tools/testing/selftests/vDSO/vdso_test_getrandom.c new file mode 100644 index 000000000000..7184e633cec7 --- /dev/null +++ b/tools/testing/selftests/vDSO/vdso_test_getrandom.c @@ -0,0 +1,283 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2022 Jason A. Donenfeld . All Rights Reserved. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest.h" +#include "parse_vdso.h" + +#ifndef timespecsub +#define timespecsub(tsp, usp, vsp) \ + do { \ + (vsp)->tv_sec = (tsp)->tv_sec - (usp)->tv_sec; \ + (vsp)->tv_nsec = (tsp)->tv_nsec - (usp)->tv_nsec; \ + if ((vsp)->tv_nsec < 0) { \ + (vsp)->tv_sec--; \ + (vsp)->tv_nsec += 1000000000L; \ + } \ + } while (0) +#endif + +static void *vgetrandom_alloc(unsigned int *num, unsigned int *size_per_each) +{ + enum { __NR_vgetrandom_alloc = 451 }; + *size_per_each = 0; + return (void *)syscall(__NR_vgetrandom_alloc, num, size_per_each, 0, 0); +} + +static struct { + pthread_mutex_t lock; + void **states; + size_t len, cap; +} grnd_allocator = { + .lock = PTHREAD_MUTEX_INITIALIZER +}; + +static void *vgetrandom_get_state(void) +{ + void *state = NULL; + + pthread_mutex_lock(&grnd_allocator.lock); + if (!grnd_allocator.len) { + size_t new_cap; + size_t page_size = getpagesize(); + unsigned int num = sysconf(_SC_NPROCESSORS_ONLN); /* Could be arbitrary, just a hint. */ + unsigned int size_per_each; + void *new_block = vgetrandom_alloc(&num, &size_per_each); + void *new_states; + + if (new_block == MAP_FAILED) + goto out; + new_cap = grnd_allocator.cap + num; + new_states = reallocarray(grnd_allocator.states, new_cap, sizeof(*grnd_allocator.states)); + if (!new_states) { + munmap(new_block, num * size_per_each); + goto out; + } + grnd_allocator.cap = new_cap; + grnd_allocator.states = new_states; + + for (size_t i = 0; i < num; ++i) { + grnd_allocator.states[i] = new_block; + if (((uintptr_t)new_block & (page_size - 1)) + size_per_each > page_size) + new_block = (void *)(((uintptr_t)new_block + page_size) & (page_size - 1)); + else + new_block += size_per_each; + } + grnd_allocator.len = num; + } + state = grnd_allocator.states[--grnd_allocator.len]; + +out: + pthread_mutex_unlock(&grnd_allocator.lock); + return state; +} + +static void vgetrandom_put_state(void *state) +{ + if (!state) + return; + pthread_mutex_lock(&grnd_allocator.lock); + grnd_allocator.states[grnd_allocator.len++] = state; + pthread_mutex_unlock(&grnd_allocator.lock); +} + +static struct { + ssize_t(*fn)(void *buf, size_t len, unsigned long flags, void *state); + pthread_key_t key; + pthread_once_t initialized; +} grnd_ctx = { + .initialized = PTHREAD_ONCE_INIT +}; + +static void vgetrandom_init(void) +{ + if (pthread_key_create(&grnd_ctx.key, vgetrandom_put_state) != 0) + return; + unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR); + if (!sysinfo_ehdr) { + printf("AT_SYSINFO_EHDR is not present!\n"); + exit(KSFT_SKIP); + } + vdso_init_from_sysinfo_ehdr(sysinfo_ehdr); + grnd_ctx.fn = (__typeof__(grnd_ctx.fn))vdso_sym("LINUX_2.6", "__vdso_getrandom"); + if (!grnd_ctx.fn) { + printf("__vdso_getrandom is missing!\n"); + exit(KSFT_FAIL); + } +} + +static ssize_t vgetrandom(void *buf, size_t len, unsigned long flags) +{ + void *state; + + pthread_once(&grnd_ctx.initialized, vgetrandom_init); + state = pthread_getspecific(grnd_ctx.key); + if (!state) { + state = vgetrandom_get_state(); + if (pthread_setspecific(grnd_ctx.key, state) != 0) { + vgetrandom_put_state(state); + state = NULL; + } + if (!state) { + printf("vgetrandom_get_state failed!\n"); + exit(KSFT_FAIL); + } + } + return grnd_ctx.fn(buf, len, flags, state); +} + +enum { TRIALS = 25000000, THREADS = 256 }; + +static void *test_vdso_getrandom(void *) +{ + for (size_t i = 0; i < TRIALS; ++i) { + unsigned int val; + ssize_t ret = vgetrandom(&val, sizeof(val), 0); + assert(ret == sizeof(val)); + } + return NULL; +} + +static void *test_libc_getrandom(void *) +{ + for (size_t i = 0; i < TRIALS; ++i) { + unsigned int val; + ssize_t ret = getrandom(&val, sizeof(val), 0); + assert(ret == sizeof(val)); + } + return NULL; +} + +static void *test_syscall_getrandom(void *) +{ + for (size_t i = 0; i < TRIALS; ++i) { + unsigned int val; + ssize_t ret = syscall(SYS_getrandom, &val, sizeof(val), 0); + assert(ret == sizeof(val)); + } + return NULL; +} + +static void bench_single(void) +{ + struct timespec start, end, diff; + + clock_gettime(CLOCK_MONOTONIC, &start); + test_vdso_getrandom(NULL); + clock_gettime(CLOCK_MONOTONIC, &end); + timespecsub(&end, &start, &diff); + printf(" vdso: %u times in %lu.%09lu seconds\n", TRIALS, diff.tv_sec, diff.tv_nsec); + + clock_gettime(CLOCK_MONOTONIC, &start); + test_libc_getrandom(NULL); + clock_gettime(CLOCK_MONOTONIC, &end); + timespecsub(&end, &start, &diff); + printf(" libc: %u times in %lu.%09lu seconds\n", TRIALS, diff.tv_sec, diff.tv_nsec); + + clock_gettime(CLOCK_MONOTONIC, &start); + test_syscall_getrandom(NULL); + clock_gettime(CLOCK_MONOTONIC, &end); + timespecsub(&end, &start, &diff); + printf("syscall: %u times in %lu.%09lu seconds\n", TRIALS, diff.tv_sec, diff.tv_nsec); +} + +static void bench_multi(void) +{ + struct timespec start, end, diff; + pthread_t threads[THREADS]; + + clock_gettime(CLOCK_MONOTONIC, &start); + for (size_t i = 0; i < THREADS; ++i) + assert(pthread_create(&threads[i], NULL, test_vdso_getrandom, NULL) == 0); + for (size_t i = 0; i < THREADS; ++i) + pthread_join(threads[i], NULL); + clock_gettime(CLOCK_MONOTONIC, &end); + timespecsub(&end, &start, &diff); + printf(" vdso: %u x %u times in %lu.%09lu seconds\n", TRIALS, THREADS, diff.tv_sec, diff.tv_nsec); + + clock_gettime(CLOCK_MONOTONIC, &start); + for (size_t i = 0; i < THREADS; ++i) + assert(pthread_create(&threads[i], NULL, test_libc_getrandom, NULL) == 0); + for (size_t i = 0; i < THREADS; ++i) + pthread_join(threads[i], NULL); + clock_gettime(CLOCK_MONOTONIC, &end); + timespecsub(&end, &start, &diff); + printf(" libc: %u x %u times in %lu.%09lu seconds\n", TRIALS, THREADS, diff.tv_sec, diff.tv_nsec); + + clock_gettime(CLOCK_MONOTONIC, &start); + for (size_t i = 0; i < THREADS; ++i) + assert(pthread_create(&threads[i], NULL, test_syscall_getrandom, NULL) == 0); + for (size_t i = 0; i < THREADS; ++i) + pthread_join(threads[i], NULL); + clock_gettime(CLOCK_MONOTONIC, &end); + timespecsub(&end, &start, &diff); + printf(" syscall: %u x %u times in %lu.%09lu seconds\n", TRIALS, THREADS, diff.tv_sec, diff.tv_nsec); +} + +static void fill(void) +{ + uint8_t weird_size[323929]; + for (;;) + vgetrandom(weird_size, sizeof(weird_size), 0); +} + +static void kselftest(void) +{ + uint8_t weird_size[1263]; + + ksft_print_header(); + ksft_set_plan(1); + + for (size_t i = 0; i < 1000; ++i) { + ssize_t ret = vgetrandom(weird_size, sizeof(weird_size), 0); + if (ret != sizeof(weird_size)) + exit(KSFT_FAIL); + } + + ksft_test_result_pass("getrandom: PASS\n"); + exit(KSFT_PASS); +} + +static void usage(const char *argv0) +{ + fprintf(stderr, "Usage: %s [bench-single|bench-multi|fill]\n", argv0); +} + +int main(int argc, char *argv[]) +{ + if (argc == 1) { + kselftest(); + return 0; + } + + if (argc != 2) { + usage(argv[0]); + return 1; + } + if (!strcmp(argv[1], "bench-single")) + bench_single(); + else if (!strcmp(argv[1], "bench-multi")) + bench_multi(); + else if (!strcmp(argv[1], "fill")) + fill(); + else { + usage(argv[0]); + return 1; + } + return 0; +}