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Groups > linux.kernel > #1686937
| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" |
| Date | 2017-07-13 23:40 +0200 |
| Message-ID | <u2U01-2vO-5@gated-at.bofh.it> (permalink) |
| References | (5 earlier) <u2QIO-ye-11@gated-at.bofh.it> <u2Rlv-Ow-1@gated-at.bofh.it> <u2SUi-1Tu-21@gated-at.bofh.it> <u2T3Z-1WG-25@gated-at.bofh.it> <u2TGF-2pl-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Jul 13, 2017 at 02:12:45PM -0700, Matthias Kaehlcke wrote:
> El Thu, Jul 13, 2017 at 03:34:16PM -0500 Josh Poimboeuf ha dit:
> > And yet another one to try (clobbering sp) :-)
> >
> > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> > index 11433f9..21f0c39 100644
> > --- a/arch/x86/include/asm/uaccess.h
> > +++ b/arch/x86/include/asm/uaccess.h
> > @@ -166,12 +166,12 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
> > ({ \
> > int __ret_gu; \
> > register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
> > - register void *__sp asm(_ASM_SP); \
> > __chk_user_ptr(ptr); \
> > might_fault(); \
> > - asm volatile("call __get_user_%P4" \
> > - : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \
> > - : "0" (ptr), "i" (sizeof(*(ptr)))); \
> > + asm volatile("call __get_user_%P3" \
> > + : "=a" (__ret_gu), "=r" (__val_gu) \
> > + : "0" (ptr), "i" (sizeof(*(ptr))) \
> > + : "sp"); \
> > (x) = (__force __typeof__(*(ptr))) __val_gu; \
> > __builtin_expect(__ret_gu, 0); \
> > })
>
> This compiles with both gcc and clang, clang does not corrupt the
> stack pointer. I wouldn't be able to tell though if it forces a stack
> frame if it doesn't already exist, as the original patch intends.
Whether it forces the stack frame on clang is a very minor issue
compared to the double fault. That really only matters when you want to
use CONFIG_STACK_VALIDATION to get 100% reliable stacktraces with frame
pointers. And that feature is currently very GCC-specific. So you
probably don't need to worry about that for now, at least until you want
to do live patching with a clang-compiled kernel.
IIRC, clobbering SP does at least force the stack frame on GCC, though I
need to double check that. I can try to work up an official patch in
the next week or so (need to do some testing first).
--
Josh
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[PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-12 23:30 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 00:20 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-13 00:30 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 00:40 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 00:40 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 20:10 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-13 20:50 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 21:30 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Michael Davidson <md@google.com> - 2017-07-13 21:40 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 22:20 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Andrey Rybainin <ryabinin.a.a@gmail.com> - 2017-07-13 22:30 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 22:40 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-13 23:20 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-13 23:40 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-14 00:00 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-13 23:20 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Andrey Rybainin <ryabinin.a.a@gmail.com> - 2017-07-13 23:30 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke <mka@chromium.org> - 2017-07-13 23:50 +0200
Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Josh Poimboeuf <jpoimboe@redhat.com> - 2017-07-14 00:00 +0200
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