Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | 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 |
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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" \
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