Re: [PATCH v6 08/13] arm64: expose user PAC bit positions via ptrace

[Richard Henderson]

On 12/7/18 12:39 PM, Kristina Martsenko wrote:
> From: Mark Rutland <mark.rutland@xxxxxxx>
> 
> When pointer authentication is in use, data/instruction pointers have a
> number of PAC bits inserted into them. The number and position of these
> bits depends on the configured TCR_ELx.TxSZ and whether tagging is
> enabled. ARMv8.3 allows tagging to differ for instruction and data
> pointers.
> 
> For userspace debuggers to unwind the stack and/or to follow pointer
> chains, they need to be able to remove the PAC bits before attempting to
> use a pointer.
> 
> This patch adds a new structure with masks describing the location of
> the PAC bits in userspace instruction and data pointers (i.e. those
> addressable via TTBR0), which userspace can query via PTRACE_GETREGSET.
> By clearing these bits from pointers (and replacing them with the value
> of bit 55), userspace can acquire the PAC-less versions.
> 
> This new regset is exposed when the kernel is built with (user) pointer
> authentication support, and the address authentication feature is
> enabled. Otherwise, the regset is hidden.
> 
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Kristina Martsenko <kristina.martsenko@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Ramana Radhakrishnan <ramana.radhakrishnan@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> ---
>  arch/arm64/include/asm/pointer_auth.h |  8 ++++++++
>  arch/arm64/include/uapi/asm/ptrace.h  |  7 +++++++
>  arch/arm64/kernel/ptrace.c            | 38 +++++++++++++++++++++++++++++++++++
>  include/uapi/linux/elf.h              |  1 +
>  4 files changed, 54 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@xxxxxxxxxx>


r~