x86/fpu: XRSTOR is expected to raise #GP
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Message ID 20181126172706.184008-1-jannh@google.com
State New
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  • x86/fpu: XRSTOR is expected to raise #GP
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Commit Message

Jann Horn Nov. 26, 2018, 5:27 p.m. UTC
commit 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess
fixups") incorrectly replaced the fixup entry for XSTATE_OP with a
user-#PF-only fixup. However, XRSTOR can also raise #GP when the supplied
address points to userspace memory. Change it back.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Fixes: 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess fixups")
Signed-off-by: Jann Horn <jannh@google.com>
---
 arch/x86/include/asm/fpu/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Sebastian Andrzej Siewior Nov. 26, 2018, 5:49 p.m. UTC | #1
On 2018-11-26 18:27:06 [+0100], Jann Horn wrote:
> commit 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess
> fixups") incorrectly replaced the fixup entry for XSTATE_OP with a
> user-#PF-only fixup. However, XRSTOR can also raise #GP when the supplied
> address points to userspace memory. Change it back.

The #GP is raised if the xstate content is invalid. But I guess the
details don't matter.

> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Fixes: 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess fixups")
> Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

> ---
>  arch/x86/include/asm/fpu/internal.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
> index 5f7290e6e954..69dcdf195b61 100644
> --- a/arch/x86/include/asm/fpu/internal.h
> +++ b/arch/x86/include/asm/fpu/internal.h
> @@ -226,7 +226,7 @@ static inline void copy_fxregs_to_kernel(struct fpu *fpu)
>  		     "3: movl $-2,%[err]\n\t"				\
>  		     "jmp 2b\n\t"					\
>  		     ".popsection\n\t"					\
> -		     _ASM_EXTABLE_UA(1b, 3b)				\
> +		     _ASM_EXTABLE(1b, 3b)				\

So you revert to what we had before. That works, tested.

>  		     : [err] "=r" (err)					\
>  		     : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)	\
>  		     : "memory")
> -- 
> 2.20.0.rc0.387.gc7a69e6b6c-goog

Sebastian
H. Peter Anvin Nov. 26, 2018, 7:49 p.m. UTC | #2
On 11/26/18 9:49 AM, Sebastian Andrzej Siewior wrote:
> On 2018-11-26 18:27:06 [+0100], Jann Horn wrote:
>> commit 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess
>> fixups") incorrectly replaced the fixup entry for XSTATE_OP with a
>> user-#PF-only fixup. However, XRSTOR can also raise #GP when the supplied
>> address points to userspace memory. Change it back.
> 
> The #GP is raised if the xstate content is invalid. But I guess the
> details don't matter.
> 
>> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Fixes: 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess fixups")
>> Signed-off-by: Jann Horn <jannh@google.com>
> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 

It does matter -- please correct the patch description, or we might have some
serious confusion at some arbitrary point in the future with the result that
the bug gets re-introduced; it would not be the first time.

	-hpa
David Laight Nov. 28, 2018, 3:27 p.m. UTC | #3
From: H. Peter Anvin
> Sent: 26 November 2018 19:50
> On 11/26/18 9:49 AM, Sebastian Andrzej Siewior wrote:
> > On 2018-11-26 18:27:06 [+0100], Jann Horn wrote:
> >> commit 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess
> >> fixups") incorrectly replaced the fixup entry for XSTATE_OP with a
> >> user-#PF-only fixup. However, XRSTOR can also raise #GP when the supplied
> >> address points to userspace memory. Change it back.
> >
> > The #GP is raised if the xstate content is invalid. But I guess the
> > details don't matter.
> >
> >> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> >> Fixes: 75045f77f7a7 ("x86/extable: Introduce _ASM_EXTABLE_UA for uaccess fixups")
> >> Signed-off-by: Jann Horn <jannh@google.com>
> > Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> >
> 
> It does matter -- please correct the patch description, or we might have some
> serious confusion at some arbitrary point in the future with the result that
> the bug gets re-introduced; it would not be the first time.

Better still note it in the code.

	David

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Sebastian Andrzej Siewior Nov. 28, 2018, 3:34 p.m. UTC | #4
On 2018-11-28 15:27:28 [+0000], David Laight wrote:
> Better still note it in the code.

I'm in favour of adding something to tools/testing/selftests/x86/.

> 	David

Sebastian

Patch
diff mbox series

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 5f7290e6e954..69dcdf195b61 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -226,7 +226,7 @@  static inline void copy_fxregs_to_kernel(struct fpu *fpu)
 		     "3: movl $-2,%[err]\n\t"				\
 		     "jmp 2b\n\t"					\
 		     ".popsection\n\t"					\
-		     _ASM_EXTABLE_UA(1b, 3b)				\
+		     _ASM_EXTABLE(1b, 3b)				\
 		     : [err] "=r" (err)					\
 		     : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)	\
 		     : "memory")