Re: [PATCH] x86: Check corrupted return address when unwinding stack

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/21/22 14:42, H.J. Lu via Gcc-patches wrote:
> If shadow stack is enabled, when unwinding stack, we count how many stack
> frames we pop to reach the landing pad and adjust shadow stack by the same
> amount.  When counting the stack frame, we compare the return address on
> normal stack against the return address on shadow stack.  If they don't
> match, return _URC_FATAL_PHASE2_ERROR for the corrupted return address on
> normal stack.  Don't check the return address for
>
> 1. Non-catchable exception where exception_class == 0.  Process will be
> terminated.
> 2. Zero return address which marks the outermost stack frame.
> 3. Signal stack frame since kernel puts a restore token on shadow stack.
>
> 	* unwind-generic.h (_Unwind_Frames_Increment): Add the EXC
> 	argument.
> 	* unwind.inc (_Unwind_RaiseException_Phase2): Pass EXC to
> 	_Unwind_Frames_Increment.
> 	(_Unwind_ForcedUnwind_Phase2): Likewise.
> 	* config/i386/shadow-stack-unwind.h (_Unwind_Frames_Increment):
> 	Take the EXC argument.  Return _URC_FATAL_PHASE2_ERROR if the
> 	return address on normal stack doesn't match the return address
> 	on shadow stack.

The generic bits are fine.  While I'm aware of one other target that 
_might_ need adjustment, it's an out-of-tree target and thus clearly not 
your responsibility.


jeff