From 7ad816762f9bf89e940e618ea40c43138b479e10 Mon Sep 17 00:00:00 2001 From: Petteri Aimonen Date: Tue, 16 Jun 2020 11:12:57 +0200 Subject: [PATCH] x86/fpu: Reset MXCSR to default in kernel_fpu_begin() Previously, kernel floating point code would run with the MXCSR control register value last set by userland code by the thread that was active on the CPU core just before kernel call. This could affect calculation results if rounding mode was changed, or a crash if a FPU/SIMD exception was unmasked. Restore MXCSR to the kernel's default value. [ bp: Carve out from a bigger patch by Petteri, add feature check, add FNINIT call too (amluto). ] Signed-off-by: Petteri Aimonen Signed-off-by: Borislav Petkov Link: https://bugzilla.kernel.org/show_bug.cgi?id=207979 Link: https://lkml.kernel.org/r/20200624114646.28953-2-bp@alien8.de --- arch/x86/include/asm/fpu/internal.h | 5 +++++ arch/x86/kernel/fpu/core.c | 6 ++++++ 2 files changed, 11 insertions(+) diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h index 42159f45bf9c..845e7481ab77 100644 --- a/arch/x86/include/asm/fpu/internal.h +++ b/arch/x86/include/asm/fpu/internal.h @@ -623,6 +623,11 @@ static inline void switch_fpu_finish(struct fpu *new_fpu) * MXCSR and XCR definitions: */ +static inline void ldmxcsr(u32 mxcsr) +{ + asm volatile("ldmxcsr %0" :: "m" (mxcsr)); +} + extern unsigned int mxcsr_feature_mask; #define XCR_XFEATURE_ENABLED_MASK 0x00000000 diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 06c818967bb6..15247b96c6ea 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -101,6 +101,12 @@ void kernel_fpu_begin(void) copy_fpregs_to_fpstate(¤t->thread.fpu); } __cpu_invalidate_fpregs_state(); + + if (boot_cpu_has(X86_FEATURE_XMM)) + ldmxcsr(MXCSR_DEFAULT); + + if (boot_cpu_has(X86_FEATURE_FPU)) + asm volatile ("fninit"); } EXPORT_SYMBOL_GPL(kernel_fpu_begin);