From 394db20ca240741a08d472173db13d6f6a6e5a28 Mon Sep 17 00:00:00 2001 From: yu-cheng yu Date: Wed, 6 Jan 2016 14:24:54 -0800 Subject: [PATCH] x86/fpu: Disable AVX when eagerfpu is off When "eagerfpu=off" is given as a command-line input, the kernel should disable AVX support. The Task Switched bit used for lazy context switching does not support AVX. If AVX is enabled without eagerfpu context switching, one task's AVX state could become corrupted or leak to other tasks. This is a bug and has bad security implications. This only affects systems that have AVX/AVX2/AVX512 and this issue will be found only when one actually uses AVX/AVX2/AVX512 _AND_ does eagerfpu=off. Reference: Intel Software Developer's Manual Vol. 3A Sec. 2.5 Control Registers: TS Task Switched bit (bit 3 of CR0) -- Allows the saving of the x87 FPU/ MMX/SSE/SSE2/SSE3/SSSE3/SSE4 context on a task switch to be delayed until an x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction is actually executed by the new task. Sec. 13.4.1 Using the TS Flag to Control the Saving of the X87 FPU and SSE State When the TS flag is set, the processor monitors the instruction stream for x87 FPU, MMX, SSE instructions. When the processor detects one of these instructions, it raises a device-not-available exeception (#NM) prior to executing the instruction. Signed-off-by: Yu-cheng Yu Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Quentin Casasnovas Cc: Ravi V. Shankar Cc: Sai Praneeth Prakhya Cc: Thomas Gleixner Cc: yu-cheng yu Link: http://lkml.kernel.org/r/1452119094-7252-5-git-send-email-yu-cheng.yu@intel.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/fpu/xstate.h | 11 ++++++----- arch/x86/kernel/fpu/init.c | 6 ++++++ 2 files changed, 12 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index 3a6c89b70307..af30fdeb140d 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -20,15 +20,16 @@ /* Supported features which support lazy state saving */ #define XFEATURE_MASK_LAZY (XFEATURE_MASK_FP | \ - XFEATURE_MASK_SSE | \ + XFEATURE_MASK_SSE) + +/* Supported features which require eager state saving */ +#define XFEATURE_MASK_EAGER (XFEATURE_MASK_BNDREGS | \ + XFEATURE_MASK_BNDCSR | \ XFEATURE_MASK_YMM | \ - XFEATURE_MASK_OPMASK | \ + XFEATURE_MASK_OPMASK | \ XFEATURE_MASK_ZMM_Hi256 | \ XFEATURE_MASK_Hi16_ZMM) -/* Supported features which require eager state saving */ -#define XFEATURE_MASK_EAGER (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR) - /* All currently supported features */ #define XCNTXT_MASK (XFEATURE_MASK_LAZY | XFEATURE_MASK_EAGER) diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index f0ab36844a6d..6d9f0a7ef4c8 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -300,6 +300,12 @@ u64 __init fpu__get_supported_xfeatures_mask(void) static void __init fpu__clear_eager_fpu_features(void) { setup_clear_cpu_cap(X86_FEATURE_MPX); + setup_clear_cpu_cap(X86_FEATURE_AVX); + setup_clear_cpu_cap(X86_FEATURE_AVX2); + setup_clear_cpu_cap(X86_FEATURE_AVX512F); + setup_clear_cpu_cap(X86_FEATURE_AVX512PF); + setup_clear_cpu_cap(X86_FEATURE_AVX512ER); + setup_clear_cpu_cap(X86_FEATURE_AVX512CD); } /* -- 2.20.1