| Message ID | 20180125103131.19168-3-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | efi/arm64: unmap the kernel during runtime service calls | expand |
Hi Ard, On Thu, Jan 25, 2018 at 10:31:29AM +0000, Ard Biesheuvel wrote: > As a preparatory step towards unmapping the kernel entirely while > executing UEFI runtime services, move the stack and the entry > wrapper routine mappings into the EFI page tables. Also, create a > vector table that overrides the main one while executing in the > firmware so we will be able to remap/unmap the kernel while taking > interrupts. [...] > + .macro ventry > + .align 7 > +.Lv\@ : stp x29, x30, [sp, #-16]! // preserve x29 and x30 > + mrs x29, elr_el1 // preserve ELR > + adr x30, .Lret // take return address > + msr elr_el1, x30 // set ELR to return address Oh man, are you really doing two ERETs for a single exception, or am I missing something? > + ldr x30, 2b // take address of 'vectors' > + msr vbar_el1, x30 // set VBAR to 'vectors' > + isb > + add x30, x30, #.Lv\@ - __efi_rt_vectors > + br x30 > + .endm > + > +.Lret: msr elr_el1, x29 If you take an IRQ here, aren't you toast? > + adr x30, __efi_rt_vectors > + msr vbar_el1, x30 > + isb > + ldp x29, x30, [sp], #16 > + eret > + > + .align 11 > +__efi_rt_vectors: > + .rept 8 > + ventry > + .endr Have you thought about SDEI at all? I can't see any code here to handle that. > + /* > + * EFI runtime services never drop to EL0, so the > + * remaining vector table entries are not needed. > + */ > diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c > index af4f943cffac..68c920b2f4f0 100644 > --- a/arch/arm64/kernel/efi.c > +++ b/arch/arm64/kernel/efi.c > @@ -130,3 +130,27 @@ asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f) > pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f); > return s; > } > + > +bool on_efi_stack(unsigned long sp) > +{ > + return sp >= EFI_STACK_BASE && sp < (EFI_STACK_BASE + EFI_STACK_SIZE); > +} > + > +int __init efi_allocate_runtime_regions(struct mm_struct *mm) > +{ > + static u8 stack[EFI_STACK_SIZE] __page_aligned_bss; Probably just me, but the use of a function static variable in a function annotated with __init just makes me feel uneasy. Could we move it out into wider scope? > + > + /* map the stack */ > + create_pgd_mapping(mm, __pa_symbol(stack), > + EFI_STACK_BASE, EFI_STACK_SIZE, > + __pgprot(pgprot_val(PAGE_KERNEL) | PTE_NG), > + false); > + > + /* map the runtime wrapper pivot function */ > + create_pgd_mapping(mm, __pa_symbol(__efi_rt_asm_wrapper), > + EFI_CODE_BASE, EFI_CODE_SIZE, > + __pgprot(pgprot_val(PAGE_KERNEL_ROX) | PTE_NG), > + false); > + > + return 0; > +} > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index b34e717d7597..3bab6c60a12b 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -204,6 +204,7 @@ alternative_if ARM64_HAS_PAN > alternative_else_nop_endif > > .if \el != 0 > + tbz x21, #63, 1f // skip if TTBR0 covers the stack So this is really a "detect EFI" check, right? Maybe comment it as such. Also, probably want to check bit 55 just in case tagging ever takes off. Will -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 26 January 2018 at 16:57, Will Deacon <will.deacon@arm.com> wrote: > Hi Ard, > > On Thu, Jan 25, 2018 at 10:31:29AM +0000, Ard Biesheuvel wrote: >> As a preparatory step towards unmapping the kernel entirely while >> executing UEFI runtime services, move the stack and the entry >> wrapper routine mappings into the EFI page tables. Also, create a >> vector table that overrides the main one while executing in the >> firmware so we will be able to remap/unmap the kernel while taking >> interrupts. > > [...] > >> + .macro ventry >> + .align 7 >> +.Lv\@ : stp x29, x30, [sp, #-16]! // preserve x29 and x30 >> + mrs x29, elr_el1 // preserve ELR >> + adr x30, .Lret // take return address >> + msr elr_el1, x30 // set ELR to return address > > Oh man, are you really doing two ERETs for a single exception, or am I > missing something? > Yes. I told you it was poetry. >> + ldr x30, 2b // take address of 'vectors' >> + msr vbar_el1, x30 // set VBAR to 'vectors' >> + isb >> + add x30, x30, #.Lv\@ - __efi_rt_vectors >> + br x30 >> + .endm >> + >> +.Lret: msr elr_el1, x29 > > If you take an IRQ here, aren't you toast? > Yep. So we need to switch this with setting the VBAR below then. >> + adr x30, __efi_rt_vectors >> + msr vbar_el1, x30 >> + isb >> + ldp x29, x30, [sp], #16 >> + eret >> + >> + .align 11 >> +__efi_rt_vectors: >> + .rept 8 >> + ventry >> + .endr > > Have you thought about SDEI at all? I can't see any code here to handle > that. > Nope >> + /* >> + * EFI runtime services never drop to EL0, so the >> + * remaining vector table entries are not needed. >> + */ >> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c >> index af4f943cffac..68c920b2f4f0 100644 >> --- a/arch/arm64/kernel/efi.c >> +++ b/arch/arm64/kernel/efi.c >> @@ -130,3 +130,27 @@ asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f) >> pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f); >> return s; >> } >> + >> +bool on_efi_stack(unsigned long sp) >> +{ >> + return sp >= EFI_STACK_BASE && sp < (EFI_STACK_BASE + EFI_STACK_SIZE); >> +} >> + >> +int __init efi_allocate_runtime_regions(struct mm_struct *mm) >> +{ >> + static u8 stack[EFI_STACK_SIZE] __page_aligned_bss; > > Probably just me, but the use of a function static variable in a function > annotated with __init just makes me feel uneasy. Could we move it out into > wider scope? > Should be fine, but I don't mind moving it out. >> + >> + /* map the stack */ >> + create_pgd_mapping(mm, __pa_symbol(stack), >> + EFI_STACK_BASE, EFI_STACK_SIZE, >> + __pgprot(pgprot_val(PAGE_KERNEL) | PTE_NG), >> + false); >> + >> + /* map the runtime wrapper pivot function */ >> + create_pgd_mapping(mm, __pa_symbol(__efi_rt_asm_wrapper), >> + EFI_CODE_BASE, EFI_CODE_SIZE, >> + __pgprot(pgprot_val(PAGE_KERNEL_ROX) | PTE_NG), >> + false); >> + >> + return 0; >> +} >> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S >> index b34e717d7597..3bab6c60a12b 100644 >> --- a/arch/arm64/kernel/entry.S >> +++ b/arch/arm64/kernel/entry.S >> @@ -204,6 +204,7 @@ alternative_if ARM64_HAS_PAN >> alternative_else_nop_endif >> >> .if \el != 0 >> + tbz x21, #63, 1f // skip if TTBR0 covers the stack > > So this is really a "detect EFI" check, right? Maybe comment it as such. > Also, probably want to check bit 55 just in case tagging ever takes off. > Right. So just bit #55 should be sufficient then, right? -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jan 26, 2018 at 05:03:29PM +0000, Ard Biesheuvel wrote: > On 26 January 2018 at 16:57, Will Deacon <will.deacon@arm.com> wrote: > > On Thu, Jan 25, 2018 at 10:31:29AM +0000, Ard Biesheuvel wrote: > >> As a preparatory step towards unmapping the kernel entirely while > >> executing UEFI runtime services, move the stack and the entry > >> wrapper routine mappings into the EFI page tables. Also, create a > >> vector table that overrides the main one while executing in the > >> firmware so we will be able to remap/unmap the kernel while taking > >> interrupts. > > > > [...] > > > >> + .macro ventry > >> + .align 7 > >> +.Lv\@ : stp x29, x30, [sp, #-16]! // preserve x29 and x30 > >> + mrs x29, elr_el1 // preserve ELR > >> + adr x30, .Lret // take return address > >> + msr elr_el1, x30 // set ELR to return address > > > > Oh man, are you really doing two ERETs for a single exception, or am I > > missing something? > > > > Yes. I told you it was poetry. We should organise a recital. > >> + ldr x30, 2b // take address of 'vectors' > >> + msr vbar_el1, x30 // set VBAR to 'vectors' > >> + isb > >> + add x30, x30, #.Lv\@ - __efi_rt_vectors > >> + br x30 > >> + .endm > >> + > >> +.Lret: msr elr_el1, x29 > > > > If you take an IRQ here, aren't you toast? > > > > Yep. So we need to switch this with setting the VBAR below then. Hmm, but the ELR will still be clobbered by an IRQ, so I don't see how you can make this safe unless you hack SPSR before entering the kernel vectors on the entry side. > >> +__efi_rt_vectors: > >> + .rept 8 > >> + ventry > >> + .endr > > > > Have you thought about SDEI at all? I can't see any code here to handle > > that. > > > > Nope Add JamesM to cc ;) > >> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > >> index b34e717d7597..3bab6c60a12b 100644 > >> --- a/arch/arm64/kernel/entry.S > >> +++ b/arch/arm64/kernel/entry.S > >> @@ -204,6 +204,7 @@ alternative_if ARM64_HAS_PAN > >> alternative_else_nop_endif > >> > >> .if \el != 0 > >> + tbz x21, #63, 1f // skip if TTBR0 covers the stack > > > > So this is really a "detect EFI" check, right? Maybe comment it as such. > > Also, probably want to check bit 55 just in case tagging ever takes off. > > > > Right. So just bit #55 should be sufficient then, right? Yes, I think so. Will -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/arm/include/asm/efi.h b/arch/arm/include/asm/efi.h index 17f1f1a814ff..3a63e7cc1dfa 100644 --- a/arch/arm/include/asm/efi.h +++ b/arch/arm/include/asm/efi.h @@ -99,4 +99,9 @@ static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base, return dram_base + SZ_512M; } +static inline int efi_allocate_runtime_regions(struct mm_struct *mm) +{ + return 0; +} + #endif /* _ASM_ARM_EFI_H */ diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h index 192d791f1103..b9b09a734719 100644 --- a/arch/arm64/include/asm/efi.h +++ b/arch/arm64/include/asm/efi.h @@ -2,11 +2,13 @@ #ifndef _ASM_EFI_H #define _ASM_EFI_H +#include <asm/memory.h> + +#ifndef __ASSEMBLY__ #include <asm/boot.h> #include <asm/cpufeature.h> #include <asm/fpsimd.h> #include <asm/io.h> -#include <asm/memory.h> #include <asm/mmu_context.h> #include <asm/neon.h> #include <asm/ptrace.h> @@ -30,8 +32,9 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md); #define arch_efi_call_virt(p, f, args...) \ ({ \ efi_##f##_t *__f; \ + typeof(__efi_rt_asm_wrapper) *__wrap = (void *)EFI_CODE_BASE; \ __f = p->f; \ - __efi_rt_asm_wrapper(__f, #f, args); \ + __wrap(__f, #f, args); \ }) #define arch_efi_call_virt_teardown() \ @@ -146,4 +149,20 @@ static inline void efi_set_pgd(struct mm_struct *mm) void efi_virtmap_load(void); void efi_virtmap_unload(void); +int __init efi_allocate_runtime_regions(struct mm_struct *mm); + +#endif /* __ASSEMBLY__ */ + +/* + * When running with vmap'ed stacks, we need the base of the stack to be aligned + * appropriately, where the exact alignment depends on the page size. Let's just + * put the stack at address 0x0, which is guaranteed to be free and aligned. + */ +#define EFI_STACK_BASE 0x0 +#define EFI_STACK_SIZE THREAD_SIZE + +/* where to map the pivot code in the UEFI page tables */ +#define EFI_CODE_BASE 0x200000 +#define EFI_CODE_SIZE PAGE_SIZE + #endif /* _ASM_EFI_H */ diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 472ef944e932..b1212b3b3df5 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -72,6 +72,8 @@ static inline bool on_overflow_stack(unsigned long sp) static inline bool on_overflow_stack(unsigned long sp) { return false; } #endif +bool on_efi_stack(unsigned long sp); + /* * We can only safely access per-cpu stacks from current in a non-preemptible * context. @@ -88,6 +90,8 @@ static inline bool on_accessible_stack(struct task_struct *tsk, unsigned long sp return true; if (on_sdei_stack(sp)) return true; + if (on_efi_stack(sp)) + return true; return false; } diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S index 05235ebb336d..09e77e5edd94 100644 --- a/arch/arm64/kernel/efi-rt-wrapper.S +++ b/arch/arm64/kernel/efi-rt-wrapper.S @@ -7,7 +7,10 @@ */ #include <linux/linkage.h> +#include <asm/efi.h> + .section ".rodata", "a" + .align PAGE_SHIFT ENTRY(__efi_rt_asm_wrapper) stp x29, x30, [sp, #-32]! mov x29, sp @@ -19,6 +22,12 @@ ENTRY(__efi_rt_asm_wrapper) */ stp x1, x18, [sp, #16] + /* switch to the EFI runtime stack and vector table */ + mov sp, #EFI_STACK_BASE + EFI_STACK_SIZE + adr x1, __efi_rt_vectors + msr vbar_el1, x1 + isb + /* * We are lucky enough that no EFI runtime services take more than * 5 arguments, so all are passed in registers rather than via the @@ -32,10 +41,50 @@ ENTRY(__efi_rt_asm_wrapper) mov x4, x6 blr x8 + /* switch back to the task stack and primary vector table */ + mov sp, x29 + ldr x1, 2f + msr vbar_el1, x1 + isb + ldp x1, x2, [sp, #16] cmp x2, x18 ldp x29, x30, [sp], #32 b.ne 0f ret -0: b efi_handle_corrupted_x18 // tail call +0: ldr x8, 1f + br x8 // tail call ENDPROC(__efi_rt_asm_wrapper) + .align 3 +1: .quad efi_handle_corrupted_x18 +2: .quad vectors + + .macro ventry + .align 7 +.Lv\@ : stp x29, x30, [sp, #-16]! // preserve x29 and x30 + mrs x29, elr_el1 // preserve ELR + adr x30, .Lret // take return address + msr elr_el1, x30 // set ELR to return address + ldr x30, 2b // take address of 'vectors' + msr vbar_el1, x30 // set VBAR to 'vectors' + isb + add x30, x30, #.Lv\@ - __efi_rt_vectors + br x30 + .endm + +.Lret: msr elr_el1, x29 + adr x30, __efi_rt_vectors + msr vbar_el1, x30 + isb + ldp x29, x30, [sp], #16 + eret + + .align 11 +__efi_rt_vectors: + .rept 8 + ventry + .endr + /* + * EFI runtime services never drop to EL0, so the + * remaining vector table entries are not needed. + */ diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c index af4f943cffac..68c920b2f4f0 100644 --- a/arch/arm64/kernel/efi.c +++ b/arch/arm64/kernel/efi.c @@ -130,3 +130,27 @@ asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f) pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f); return s; } + +bool on_efi_stack(unsigned long sp) +{ + return sp >= EFI_STACK_BASE && sp < (EFI_STACK_BASE + EFI_STACK_SIZE); +} + +int __init efi_allocate_runtime_regions(struct mm_struct *mm) +{ + static u8 stack[EFI_STACK_SIZE] __page_aligned_bss; + + /* map the stack */ + create_pgd_mapping(mm, __pa_symbol(stack), + EFI_STACK_BASE, EFI_STACK_SIZE, + __pgprot(pgprot_val(PAGE_KERNEL) | PTE_NG), + false); + + /* map the runtime wrapper pivot function */ + create_pgd_mapping(mm, __pa_symbol(__efi_rt_asm_wrapper), + EFI_CODE_BASE, EFI_CODE_SIZE, + __pgprot(pgprot_val(PAGE_KERNEL_ROX) | PTE_NG), + false); + + return 0; +} diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index b34e717d7597..3bab6c60a12b 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -204,6 +204,7 @@ alternative_if ARM64_HAS_PAN alternative_else_nop_endif .if \el != 0 + tbz x21, #63, 1f // skip if TTBR0 covers the stack mrs x21, ttbr0_el1 tst x21, #TTBR_ASID_MASK // Check for the reserved ASID orr x23, x23, #PSR_PAN_BIT // Set the emulated PAN in the saved SPSR diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c index 1cc41c3d6315..e84f4d961de2 100644 --- a/drivers/firmware/efi/arm-runtime.c +++ b/drivers/firmware/efi/arm-runtime.c @@ -107,6 +107,8 @@ static bool __init efi_virtmap_init(void) if (efi_memattr_apply_permissions(&efi_mm, efi_set_mapping_permissions)) return false; + efi_allocate_runtime_regions(&efi_mm); + return true; }
As a preparatory step towards unmapping the kernel entirely while executing UEFI runtime services, move the stack and the entry wrapper routine mappings into the EFI page tables. Also, create a vector table that overrides the main one while executing in the firmware so we will be able to remap/unmap the kernel while taking interrupts. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm/include/asm/efi.h | 5 ++ arch/arm64/include/asm/efi.h | 23 ++++++++- arch/arm64/include/asm/stacktrace.h | 4 ++ arch/arm64/kernel/efi-rt-wrapper.S | 51 +++++++++++++++++++- arch/arm64/kernel/efi.c | 24 +++++++++ arch/arm64/kernel/entry.S | 1 + drivers/firmware/efi/arm-runtime.c | 2 + 7 files changed, 107 insertions(+), 3 deletions(-) -- 2.11.0 -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html