Messages in this thread Patch in this message | | | From | Amit Kachhap <> | Subject | Re: [PATCH v2 1/2] arm64/crash_core: Export KERNELPACMASK in vmcoreinfo | Date | Wed, 6 May 2020 17:32:56 +0530 |
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Hi Will,
On 5/4/20 10:47 PM, Will Deacon wrote: > On Mon, Apr 27, 2020 at 11:55:01AM +0530, Amit Daniel Kachhap wrote: >> Recently arm64 linux kernel added support for Armv8.3-A Pointer >> Authentication feature. If this feature is enabled in the kernel and the >> hardware supports address authentication then the return addresses are >> signed and stored in the stack to prevent ROP kind of attack. Kdump tool >> will now dump the kernel with signed lr values in the stack. >> >> Any user analysis tool for this kernel dump may need the kernel pac mask >> information in vmcoreinfo to generate the correct return address for >> stacktrace purpose as well as to resolve the symbol name. >> >> This patch is similar to commit ec6e822d1a22d0eef ("arm64: expose user PAC >> bit positions via ptrace") which exposes pac mask information via ptrace >> interfaces. >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> >> --- >> Changes since v1: >> * Rebased to kernel 5.7-rc3. >> * commit log change. >> >> An implementation of this new KERNELPACMASK vmcoreinfo field used by crash >> tool can be found here[1]. This change is accepted by crash utility >> maintainer [2]. >> >> [1]: https://www.redhat.com/archives/crash-utility/2020-April/msg00095.html >> [2]: https://www.redhat.com/archives/crash-utility/2020-April/msg00099.html >> >> arch/arm64/include/asm/compiler.h | 3 +++ >> arch/arm64/kernel/crash_core.c | 4 ++++ >> 2 files changed, 7 insertions(+) >> >> diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h >> index eece20d..32d5900 100644 >> --- a/arch/arm64/include/asm/compiler.h >> +++ b/arch/arm64/include/asm/compiler.h >> @@ -19,6 +19,9 @@ >> #define __builtin_return_address(val) \ >> (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) >> >> +#else /* !CONFIG_ARM64_PTR_AUTH */ >> +#define ptrauth_user_pac_mask() 0ULL >> +#define ptrauth_kernel_pac_mask() 0ULL > > This doesn't look quite right to me, since you still have to take into > account the case where CONFIG_ARM64_PTR_AUTH=y but the feature is not > available at runtime:
Yes agree with you here. However the config gaurd is saving some extra computation for __builtin_return_address. There are some compiler support being added in __builtin_extract_return_address to mask the PAC. Hopefully that will improve this code. In the meantime let it be like this.
I can remove this else case and as other users of ptrauth_{kernel,user}_pac_mask(ptrace.c) protect it with a config gaurd there.
> >> @@ -16,4 +17,7 @@ void arch_crash_save_vmcoreinfo(void) >> vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n", >> PHYS_OFFSET); >> vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset()); >> + vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n", >> + system_supports_address_auth() ? >> + ptrauth_kernel_pac_mask() : 0); > > In which case, would it make more sense to define > ptrauth_{kernel,user}_pac_mask() unconditionally? In fact, I'd probably > just remove the guards completely from asm/compiler.h because I think > they're misleading.
As answered above. Let me know your opinion. Although I don't have strong reservation in keeping the config gaurd.
Thanks, Amit Daniel
> > Will > > --->8 > > diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h > index eece20d2c55f..51a7ce87cdfe 100644 > --- a/arch/arm64/include/asm/compiler.h > +++ b/arch/arm64/include/asm/compiler.h > @@ -2,8 +2,6 @@ > #ifndef __ASM_COMPILER_H > #define __ASM_COMPILER_H > > -#if defined(CONFIG_ARM64_PTR_AUTH) > - > /* > * The EL0/EL1 pointer bits used by a pointer authentication code. > * This is dependent on TBI0/TBI1 being enabled, or bits 63:56 would also apply. > @@ -19,6 +17,4 @@ > #define __builtin_return_address(val) \ > (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val))) > > -#endif /* CONFIG_ARM64_PTR_AUTH */ > - > #endif /* __ASM_COMPILER_H */ >
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