[Crash-utility] [PATCH v2] Determine the ARM64 kernel's Pointer Authentication mask value by reading the new KERNELPACMASK vmcoreinfo entry.

[Amit Kachhap]

Hi Dave

On 4/23/20 7:17 PM, Dave Anderson wrote:
> 
> ----- Original Message -----
> ...
>>
>> A small correction, top bytes are included in KERNELPACMASK but that is
>> configurable. Anyway so when autiasp(authentication) instruction fails
>> then all obfuscated value is cleared and a error bit pattern is added
>> only in top byte.
>> As mentioned earlier armv8.6 enhanced PAC will not add bit pattern to
>> denote failure but will cause illegal instruction fault with an
>> exception class and hence pc will not have extra details. This is work
>> in progress so the current crash utility changes should work fine.
>   
> Just to be clear then, your v2 patch set should be OK to check in -- except
> for this call to is_kernel_text():
>     
>      > And then when trying to determine whether the current stack pointer is
>      > pointing to an in-kernel exception frame, the possible regs->pc and regs[30]
>      > values are both transformed with the mask, so it seems that both of them
>      > will have been obfuscated by the processor when creating the frame on
>      > the stack:
>      >
>      >    static int
>      >    arm64_is_kernel_exception_frame(struct bt_info *bt, ulong stkptr)
>      >    {
>      >            struct arm64_pt_regs *regs;
>      >            struct machine_specific *ms = machdep->machspec;
>      >
>      >            regs = (struct arm64_pt_regs *)&bt->stackbuf[(ulong)(STACK_OFFSET_TYPE(stkptr))];
>      >
>      >            if (INSTACK(regs->sp, bt) && INSTACK(regs->regs[29], bt) &&
>      >                !(regs->pstate & (0xffffffff00000000ULL | PSR_MODE32_BIT)) &&
>      > ========>     is_kernel_text(regs->pc | ms->CONFIG_ARM64_KERNELPACMASK) &&
>      
>      Yes good catch. Masking can be removed from here.
> 
> Can you please confirm?

I just posted v3 version with no checks for pc here.

Cheers,
Amit
> 
> Thanks,
>    Dave
>