From patchwork Tue Mar 16 15:33:03 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Vetter X-Patchwork-Id: 403591 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED3A1C4332E for ; Tue, 16 Mar 2021 15:34:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE1B660200 for ; Tue, 16 Mar 2021 15:34:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232943AbhCPPdx (ORCPT ); Tue, 16 Mar 2021 11:33:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238112AbhCPPdS (ORCPT ); Tue, 16 Mar 2021 11:33:18 -0400 Received: from mail-wr1-x432.google.com (mail-wr1-x432.google.com [IPv6:2a00:1450:4864:20::432]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD72FC0613D7 for ; Tue, 16 Mar 2021 08:33:16 -0700 (PDT) Received: by mail-wr1-x432.google.com with SMTP id o16so7656853wrn.0 for ; Tue, 16 Mar 2021 08:33:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=zwe0ekXmy9t5eNr3sFs9jCzA/xhMldV8JLAydoSdCfc=; b=GzG+edIxhOWO3e0C//e9ZTvwmWIMqXUh3qVGupEH1XpIfgojiM9nr7zfSbfVnLpEX1 TppZD/lYq2BFxWK6uExvqhTf4cGvOaXXXtjYXrDDvq/txY4i5BzARGuD/BQ+Nc/vZ9CP U43D7zJSOobDqMzHTu1jMNW+6MtVYMmXPpabc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=zwe0ekXmy9t5eNr3sFs9jCzA/xhMldV8JLAydoSdCfc=; b=ob450YSgsmq+Ps/BV4B5r3Mwb3+CyKaU3runh4+NznhkZByQTSLLutp7+7w+2VuSj7 sNYp9ZMp/G2YQsVaSx35zoa5+XVvRZtfOXrSrmaEju6qAL/S43amHPsZmYnauMP7wCFe fwf1nGnmrmYrn997ysJiWVsxM8iX6F1qQit6FVm4l6CLZpusGatkktckix2GEUqWxQcc VoZy3BQ0BNXqsn4QChBb5dtu0I/znW0vqKn6wnUXFlxO3bUFm6t0kZAYLOhdHlWzd12m xaoKqDCgFudXa3i5My2eqWbHRHfaa9m1NwE65hJFAiq88+F6hLV1S4e6nuV3A+57mw18 SmEg== X-Gm-Message-State: AOAM531UVUkRS0RCHpaZRiP0IyDagvH/O0rvoFet7fBXAf2JYq7LkFE2 Sy4Eyck0UJ0Ipiv0/2JJTJfzTw== X-Google-Smtp-Source: ABdhPJxsQT1ztD0lh1/0ccaL0ZTcHbZx32nTGgPOptwOia/Vap2jPDUXToCOLm5fL6HRJJsLfse8jA== X-Received: by 2002:adf:ec0b:: with SMTP id x11mr5396504wrn.175.1615908795642; Tue, 16 Mar 2021 08:33:15 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id h22sm3985078wmb.36.2021.03.16.08.33.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Mar 2021 08:33:15 -0700 (PDT) From: Daniel Vetter To: DRI Development , LKML Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, Daniel Vetter , 3pvd@google.com, Jann Horn , Paolo Bonzini , Jason Gunthorpe , Cornelia Huck , Peter Xu , Alex Williamson , Daniel Vetter Subject: [PATCH 3/3] mm: unexport follow_pfn Date: Tue, 16 Mar 2021 16:33:03 +0100 Message-Id: <20210316153303.3216674-4-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210316153303.3216674-1-daniel.vetter@ffwll.ch> References: <20210316153303.3216674-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Both kvm (in bd2fae8da794 ("KVM: do not assume PTE is writable after follow_pfn")) and vfio (in 07956b6269d3 ("vfio/type1: Use follow_pte()")) have lost their callsites of follow_pfn(). All the other ones have been switched over to unsafe_follow_pfn because they cannot be fixed without breaking userspace api. Argueably the vfio code is still racy, but that's kinda a bigger picture. But since it does leak the pte beyond where it drops the pt lock, without anything else like an mmu notifier guaranteeing coherence, the problem is at least clearly visible in the vfio code. So good enough with me. I've decided to keep the explanation that after dropping the pt lock you must have an mmu notifier if you keep using the pte somehow by adjusting it and moving it into the kerneldoc for the new follow_pte() function. Cc: 3pvd@google.com Cc: Jann Horn Cc: Paolo Bonzini Cc: Jason Gunthorpe Cc: Cornelia Huck Cc: Peter Xu Cc: Alex Williamson Cc: linux-mm@kvack.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-samsung-soc@vger.kernel.org Cc: linux-media@vger.kernel.org Cc: kvm@vger.kernel.org Signed-off-by: Daniel Vetter Reviewed-by: Jason Gunthorpe --- include/linux/mm.h | 2 -- mm/memory.c | 26 +++++--------------------- mm/nommu.c | 13 +------------ 3 files changed, 6 insertions(+), 35 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index caec8b25d66f..304588e2f829 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1693,8 +1693,6 @@ int follow_invalidate_pte(struct mm_struct *mm, unsigned long address, pmd_t **pmdpp, spinlock_t **ptlp); int follow_pte(struct mm_struct *mm, unsigned long address, pte_t **ptepp, spinlock_t **ptlp); -int follow_pfn(struct vm_area_struct *vma, unsigned long address, - unsigned long *pfn); int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, unsigned long *pfn); int follow_phys(struct vm_area_struct *vma, unsigned long address, diff --git a/mm/memory.c b/mm/memory.c index e8a145505b69..317e653c8aeb 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4724,7 +4724,10 @@ int follow_invalidate_pte(struct mm_struct *mm, unsigned long address, * should be taken for read. * * KVM uses this function. While it is arguably less bad than ``follow_pfn``, - * it is not a good general-purpose API. + * it is not a good general-purpose API: If callers use the pte after they've + * unlocked @ptlp they must ensure coherency with pte updates by using a + * &mmu_notifier to follow updates. Any caller not following these requirements + * must use unsafe_follow_pfn() instead. * * Return: zero on success, -ve otherwise. */ @@ -4735,25 +4738,7 @@ int follow_pte(struct mm_struct *mm, unsigned long address, } EXPORT_SYMBOL_GPL(follow_pte); -/** - * follow_pfn - look up PFN at a user virtual address - * @vma: memory mapping - * @address: user virtual address - * @pfn: location to store found PFN - * - * Only IO mappings and raw PFN mappings are allowed. Note that callers must - * ensure coherency with pte updates by using a &mmu_notifier to follow updates. - * If this is not feasible, or the access to the @pfn is only very short term, - * use follow_pte_pmd() instead and hold the pagetable lock for the duration of - * the access instead. Any caller not following these requirements must use - * unsafe_follow_pfn() instead. - * - * This function does not allow the caller to read the permissions - * of the PTE. Do not use it. - * - * Return: zero and the pfn at @pfn on success, -ve otherwise. - */ -int follow_pfn(struct vm_area_struct *vma, unsigned long address, +static int follow_pfn(struct vm_area_struct *vma, unsigned long address, unsigned long *pfn) { int ret = -EINVAL; @@ -4770,7 +4755,6 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address, pte_unmap_unlock(ptep, ptl); return 0; } -EXPORT_SYMBOL_GPL(follow_pfn); /** * unsafe_follow_pfn - look up PFN at a user virtual address diff --git a/mm/nommu.c b/mm/nommu.c index 1dc983f50e2c..cee29d0791b3 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -111,17 +111,7 @@ unsigned int kobjsize(const void *objp) return page_size(page); } -/** - * follow_pfn - look up PFN at a user virtual address - * @vma: memory mapping - * @address: user virtual address - * @pfn: location to store found PFN - * - * Only IO mappings and raw PFN mappings are allowed. - * - * Returns zero and the pfn at @pfn on success, -ve otherwise. - */ -int follow_pfn(struct vm_area_struct *vma, unsigned long address, +static int follow_pfn(struct vm_area_struct *vma, unsigned long address, unsigned long *pfn) { if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) @@ -130,7 +120,6 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address, *pfn = address >> PAGE_SHIFT; return 0; } -EXPORT_SYMBOL_GPL(follow_pfn); /** * unsafe_follow_pfn - look up PFN at a user virtual address