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

[Dave Anderson]

----- 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?

Thanks,
  Dave