From: Thomas Gleixner <tglx@linutronix.de>
To: Borislav Petkov <bp@alien8.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
x86@kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in restore_fpregs_from_user()
Date: Mon, 30 Aug 2021 22:09:27 +0200 [thread overview]
Message-ID: <87zgsyg0eg.ffs@tglx> (raw)
In-Reply-To: <YS0ylo9nTHD9NiAp@zn.tnic>
On Mon, Aug 30 2021 at 21:33, Borislav Petkov wrote:
> On Mon, Aug 30, 2021 at 06:27:22PM +0200, Thomas Gleixner wrote:
>> FPU restore from a signal frame can trigger various exceptions. The
>> exceptions are caught with an exception table entry. The handler of this
>> entry sets the error return value to the negated exception number.
>>
>> Any other exception than #PF is fatal and recovery is not possible. This
>> relies on the fact that the #PF exception number is the same as EFAULT, but
>> that's not really obvious.
>>
>> Check the error code for -X86_TRAP_PF instead of checking it for -EFAULT to
>> make it clear how that works.
>
> I guess you wanna fixup the comment over XSTATE_OP() too and perhaps
> mention ex_handler_fault() explicitly so that one can make her/his way
> around the code and pinpoint quickly where it sticks that exception
> number into rAX.
Something like the below?
Thanks,
tglx
---
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -88,7 +88,11 @@ static inline void fpstate_init_soft(str
#endif
extern void save_fpregs_to_fpstate(struct fpu *fpu);
-/* Returns 0 or the negated trap number, which results in -EFAULT for #PF */
+/*
+ * Returns 0 on success or the negated trap number when the operation
+ * raises an exception (The exception fixup function ex_handler_fault()
+ * stores the trap number in EAX).
+ */
#define user_insn(insn, output, input...) \
({ \
int err; \
@@ -199,7 +203,8 @@ static inline void fxsave(struct fxregs_
/*
* After this @err contains 0 on success or the negated trap number when
- * the operation raises an exception. For faults this results in -EFAULT.
+ * the operation raises an exception (The exception fixup function
+ * ex_handler_fault() stores the trap number in EAX).
*/
#define XSTATE_OP(op, st, lmask, hmask, err) \
asm volatile("1:" op "\n\t" \
next prev parent reply other threads:[~2021-08-30 20:09 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-30 16:27 [patch 00/10] x86/fpu: Clean up error handling in sigframe related code Thomas Gleixner
2021-08-30 16:27 ` [patch 01/10] x86/fpu/signal: Clarify exception handling in restore_fpregs_from_user() Thomas Gleixner
2021-08-30 19:33 ` Borislav Petkov
2021-08-30 20:07 ` Borislav Petkov
2021-08-30 20:09 ` Thomas Gleixner [this message]
2021-08-30 21:02 ` Al Viro
2021-08-30 21:26 ` Linus Torvalds
2021-08-30 21:30 ` Al Viro
2021-08-30 22:00 ` Linus Torvalds
2021-08-30 22:12 ` Thomas Gleixner
2021-08-30 22:26 ` Linus Torvalds
2021-08-31 0:06 ` Al Viro
2021-08-31 0:34 ` Thomas Gleixner
2021-08-31 7:39 ` Borislav Petkov
2021-08-31 18:39 ` Luck, Tony
2021-09-01 7:27 ` Borislav Petkov
2021-08-30 22:01 ` Thomas Gleixner
2021-08-30 22:11 ` Linus Torvalds
2021-09-01 12:00 ` Thomas Gleixner
2021-09-01 15:52 ` Thomas Gleixner
2021-09-01 16:47 ` Sean Christopherson
2021-09-01 19:22 ` Thomas Gleixner
2021-09-01 19:22 ` Dave Hansen
2021-09-02 13:08 ` Jarkko Sakkinen
2021-09-02 14:08 ` Thomas Gleixner
2021-09-03 6:00 ` Jarkko Sakkinen
2021-09-03 6:05 ` Jarkko Sakkinen
2021-08-30 16:27 ` [patch 02/10] x86/fpu/signal: Move header zeroing out of xsave_to_user_sigframe() Thomas Gleixner
2021-08-30 16:27 ` [patch 03/10] x86/fpu/signal: Move xstate clearing out of copy_fpregs_to_sigframe() Thomas Gleixner
2021-08-30 16:27 ` [patch 04/10] x86/fpu/signal: Change return type of copy_fpstate_to_sigframe() to boolean Thomas Gleixner
2021-08-30 16:27 ` [patch 05/10] x86/fpu/signal: Change return type of copy_fpregs_to_sigframe() helpers " Thomas Gleixner
2021-08-30 16:27 ` [patch 06/10] x86/signal: Change return type of restore_sigcontext() " Thomas Gleixner
2021-08-30 16:27 ` [patch 07/10] x86/fpu/signal: Change return type of fpu__restore_sig() " Thomas Gleixner
2021-08-30 16:27 ` [patch 08/10] x86/fpu/signal: Change return type of __fpu_restore_sig() " Thomas Gleixner
2021-08-30 16:27 ` [patch 09/10] x86/fpu/signal: Change return code of check_xstate_in_sigframe() " Thomas Gleixner
2021-08-30 16:27 ` [patch 10/10] x86/fpu/signal: Change return code of restore_fpregs_from_user() " Thomas Gleixner
2021-08-30 17:39 ` [patch 00/10] x86/fpu: Clean up error handling in sigframe related code Linus Torvalds
2021-08-30 18:51 ` Thomas Gleixner
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