Re: [PATCH] stack-protector: Check stack canary for noreturn function

["H.J. Lu" <hjl.tools@gmail.com>]

On Sat, Jul 30, 2022 at 1:30 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 7/14/2022 3:55 PM, H.J. Lu via Gcc-patches wrote:
> > Check stack canary for noreturn function to catch stack corruption
> > before calling noreturn function.  For C++, check stack canary when
> > throwing exception or resuming stack unwind to avoid corrupted stack.
> >
> > gcc/
> >
> >       PR middle-end/58245
> >       * calls.cc (expand_call): Check stack canary for noreturn
> >       function.
> >
> > gcc/testsuite/
> >
> >       PR middle-end/58245
> >       * c-c++-common/pr58245-1.c: New test.
> >       * g++.dg/pr58245-1.C: Likewise.
> >       * g++.dg/fstack-protector-strong.C: Adjusted.
> But is this really something we want?   I'd actually lean towards
> eliminating the useless load -- I don't necessarily think we should be
> treating non-returning paths specially here.
>
> The whole point of the stack protector is to prevent the *return* path
> from going to an attacker controlled location.  I'm not sure checking
> the protector at this point actually does anything particularly useful.

throw is marked no return.   Since the unwind library may read
the stack contents to unwind stack, it the stack is corrupted, the
exception handling may go wrong.   Should we handle this case?

 --
H.J.