Re: PING^1: [PATCH] x86: Check corrupted return address when unwinding stack

[Hongtao Liu <crazylht@gmail.com>]

On Wed, Oct 5, 2022 at 5:33 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Wed, Sep 21, 2022 at 1:42 PM H.J. Lu <hjl.tools@gmail.com> 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.
Ok.
> >
> >         * 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.
> > ---
> >  libgcc/config/i386/shadow-stack-unwind.h | 51 ++++++++++++++++++++++--
> >  libgcc/unwind-generic.h                  |  2 +-
> >  libgcc/unwind.inc                        |  4 +-
> >  3 files changed, 50 insertions(+), 7 deletions(-)
> >
> > diff --git a/libgcc/config/i386/shadow-stack-unwind.h b/libgcc/config/i386/shadow-stack-unwind.h
> > index 2b02682bdae..89d44165000 100644
> > --- a/libgcc/config/i386/shadow-stack-unwind.h
> > +++ b/libgcc/config/i386/shadow-stack-unwind.h
> > @@ -54,10 +54,39 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
> >     aligned.  If the original shadow stack is 8 byte aligned, we just
> >     need to pop 2 slots, one restore token, from shadow stack.  Otherwise,
> >     we need to pop 3 slots, one restore token + 4 byte padding, from
> > -   shadow stack.  */
> > -#ifndef __x86_64__
> > +   shadow stack.
> > +
> > +   When popping a 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.
> > + */
> >  #undef _Unwind_Frames_Increment
> > -#define _Unwind_Frames_Increment(context, frames)      \
> > +#ifdef __x86_64__
> > +#define _Unwind_Frames_Increment(exc, context, frames) \
> > +    {                                                  \
> > +      frames++;                                                \
> > +      if (exc->exception_class != 0                    \
> > +         && _Unwind_GetIP (context) != 0               \
> > +         && !_Unwind_IsSignalFrame (context))          \
> > +       {                                               \
> > +         _Unwind_Word ssp = _get_ssp ();               \
> > +         if (ssp != 0)                                 \
> > +           {                                           \
> > +             ssp += 8 * frames;                        \
> > +             _Unwind_Word ra = *(_Unwind_Word *) ssp;  \
> > +             if (ra != _Unwind_GetIP (context))        \
> > +               return _URC_FATAL_PHASE2_ERROR;         \
> > +           }                                           \
> > +       }                                               \
> > +    }
> > +#else
> > +#define _Unwind_Frames_Increment(exc, context, frames) \
> >    if (_Unwind_IsSignalFrame (context))                 \
> >      do                                                 \
> >        {                                                        \
> > @@ -83,5 +112,19 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
> >        }                                                        \
> >      while (0);                                         \
> >    else                                                 \
> > -    frames++;
> > +    {                                                  \
> > +      frames++;                                                \
> > +      if (exc->exception_class != 0                    \
> > +         && _Unwind_GetIP (context) != 0)              \
> > +       {                                               \
> > +         _Unwind_Word ssp = _get_ssp ();               \
> > +         if (ssp != 0)                                 \
> > +           {                                           \
> > +             ssp += 4 * frames;                        \
> > +             _Unwind_Word ra = *(_Unwind_Word *) ssp;  \
> > +             if (ra != _Unwind_GetIP (context))        \
> > +               return _URC_FATAL_PHASE2_ERROR;         \
> > +           }                                           \
> > +       }                                               \
> > +    }
> >  #endif
> > diff --git a/libgcc/unwind-generic.h b/libgcc/unwind-generic.h
> > index a87c9b3ccf6..bf721282d03 100644
> > --- a/libgcc/unwind-generic.h
> > +++ b/libgcc/unwind-generic.h
> > @@ -292,6 +292,6 @@ EXCEPTION_DISPOSITION _GCC_specific_handler (PEXCEPTION_RECORD, void *,
> >  #define _Unwind_Frames_Extra(frames)
> >
> >  /* Increment frame count.  */
> > -#define _Unwind_Frames_Increment(context, frames) frames++
> > +#define _Unwind_Frames_Increment(exc, context, frames) frames++
> >
> >  #endif /* unwind.h */
> > diff --git a/libgcc/unwind.inc b/libgcc/unwind.inc
> > index 5efd8af1b15..a7111a7b3a8 100644
> > --- a/libgcc/unwind.inc
> > +++ b/libgcc/unwind.inc
> > @@ -73,7 +73,7 @@ _Unwind_RaiseException_Phase2(struct _Unwind_Exception *exc,
> >        gcc_assert (!match_handler);
> >
> >        uw_update_context (context, &fs);
> > -      _Unwind_Frames_Increment (context, frames);
> > +      _Unwind_Frames_Increment (exc, context, frames);
> >      }
> >
> >    *frames_p = frames;
> > @@ -191,7 +191,7 @@ _Unwind_ForcedUnwind_Phase2 (struct _Unwind_Exception *exc,
> >        /* Update cur_context to describe the same frame as fs, and discard
> >          the previous context if necessary.  */
> >        uw_advance_context (context, &fs);
> > -      _Unwind_Frames_Increment (context, frames);
> > +      _Unwind_Frames_Increment (exc, context, frames);
> >      }
> >
> >    *frames_p = frames;
> > --
> > 2.37.3
> >
>
> PING.  Jeff has approved the generic changes.
>
> Thanks.
>
> --
> H.J.



--
BR,
Hongtao