Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | Subject | [patch V3 10/20] x86/fpu/signal: Clarify exception handling in restore_fpregs_from_user() | Date | Wed, 8 Sep 2021 15:29:26 +0200 (CEST) |
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FPU restore from a signal frame can trigger various exceptions. The exceptions are caught with an exception table entry. The handler of this entry stores the trap number in EAX. The FPU specific fixup negates that trap number to convert it into an negative error code.
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.
Remove the negation from the exception fixup as it really has no value and check for X86_TRAP_PF at the call site.
There is still confusion due to the return code conversion for the error case which will be cleaned up separately.
Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- V2: Remove the negation (Al) --- arch/x86/include/asm/fpu/internal.h | 21 ++++++++------------- arch/x86/kernel/fpu/signal.c | 5 +++-- 2 files changed, 11 insertions(+), 15 deletions(-) --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -88,7 +88,10 @@ 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 trap number when the operation raises an + * exception. + */ #define user_insn(insn, output, input...) \ ({ \ int err; \ @@ -98,11 +101,7 @@ extern void save_fpregs_to_fpstate(struc asm volatile(ASM_STAC "\n" \ "1: " #insn "\n" \ "2: " ASM_CLAC "\n" \ - ".section .fixup,\"ax\"\n" \ - "3: negl %%eax\n" \ - " jmp 2b\n" \ - ".previous\n" \ - _ASM_EXTABLE_TYPE(1b, 3b, EX_TYPE_FAULT_MCE_SAFE) \ + _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_FAULT_MCE_SAFE) \ : [err] "=a" (err), output \ : "0"(0), input); \ err; \ @@ -198,18 +197,14 @@ static inline void fxsave(struct fxregs_ #define XRSTORS ".byte " REX_PREFIX "0x0f,0xc7,0x1f" /* - * After this @err contains 0 on success or the negated trap number when - * the operation raises an exception. For faults this results in -EFAULT. + * After this @err contains 0 on success or the trap number when the + * operation raises an exception. */ #define XSTATE_OP(op, st, lmask, hmask, err) \ asm volatile("1:" op "\n\t" \ "xor %[err], %[err]\n" \ "2:\n\t" \ - ".pushsection .fixup,\"ax\"\n\t" \ - "3: negl %%eax\n\t" \ - "jmp 2b\n\t" \ - ".popsection\n\t" \ - _ASM_EXTABLE_TYPE(1b, 3b, EX_TYPE_FAULT_MCE_SAFE) \ + _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_FAULT_MCE_SAFE) \ : [err] "=a" (err) \ : "D" (st), "m" (*st), "a" (lmask), "d" (hmask) \ : "memory") --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -13,6 +13,7 @@ #include <asm/fpu/xstate.h> #include <asm/sigframe.h> +#include <asm/trapnr.h> #include <asm/trace/fpu.h> static struct _fpx_sw_bytes fx_sw_reserved __ro_after_init; @@ -275,7 +276,7 @@ static int restore_fpregs_from_user(void fpregs_unlock(); /* Try to handle #PF, but anything else is fatal. */ - if (ret != -EFAULT) + if (ret != X86_TRAP_PF) return -EINVAL; ret = fault_in_pages_readable(buf, size); @@ -405,7 +406,7 @@ static int __fpu_restore_sig(void __user u64 mask = user_xfeatures | xfeatures_mask_supervisor(); fpu->state.xsave.header.xfeatures &= mask; - ret = os_xrstor_safe(&fpu->state.xsave, xfeatures_mask_all); + ret = os_xrstor_safe(&fpu->state.xsave, xfeatures_mask_all) ? -EINVAL : 0; } else { ret = fxrstor_safe(&fpu->state.fxsave); }
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