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