From 4339d0c63c2d5bea1fe6de4091ee2fe9eeea09a7 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 8 Sep 2021 15:29:26 +0200 Subject: x86/fpu/signal: Clarify exception handling in restore_fpregs_from_user() 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 Signed-off-by: Thomas Gleixner Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/20210908132525.506192488@linutronix.de --- arch/x86/include/asm/fpu/internal.h | 21 ++++++++------------- arch/x86/kernel/fpu/signal.c | 5 +++-- 2 files changed, 11 insertions(+), 15 deletions(-) (limited to 'arch') diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index cb1ca602e848..4cfd40dc3cb5 100644 --- 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(struct swregs_state *soft) {} #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(struct fpu *fpu); 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_state *fx) #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") diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 445c57c9c539..9bfffdb64c0d 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -13,6 +13,7 @@ #include #include +#include #include static struct _fpx_sw_bytes fx_sw_reserved __ro_after_init; @@ -275,7 +276,7 @@ retry: 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 *buf, void __user *buf_fx, 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); } -- cgit v1.2.3-59-g8ed1b