Re: [PATCH v2 1/2] arm64/crash_core: Export KERNELPACMASK in vmcoreinfo

[Amit Kachhap]

Hi Will/Catalin,

On 4/27/20 11:55 AM, 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@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>

This patch user side changes are accepted by crash-utility maintainer [1]
so I think this is in a good shape to go in.

Thanks,
Amit Daniel

[1]: https://www.redhat.com/archives/crash-utility/2020-April/msg00099.html

> ---
> 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
>   #endif /* CONFIG_ARM64_PTR_AUTH */
>   
>   #endif /* __ASM_COMPILER_H */
> diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c
> index ca4c3e1..25cf2ce 100644
> --- a/arch/arm64/kernel/crash_core.c
> +++ b/arch/arm64/kernel/crash_core.c
> @@ -6,6 +6,7 @@
>   
>   #include <linux/crash_core.h>
>   #include <asm/memory.h>
> +#include <asm/pointer_auth.h>
>   
>   void arch_crash_save_vmcoreinfo(void)
>   {
> @@ -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);
>   }