From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20140512003205.607397016@1wt.eu> Date: Mon, 12 May 2014 02:33:59 +0200 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: "H. Peter Anvin" , Willy Tarreau Subject: [ 119/143] x86, fpu, amd: Clear exceptions in AMD FXSAVE workaround In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Linus Torvalds Before we do an EMMS in the AMD FXSAVE information leak workaround we need to clear any pending exceptions, otherwise we trap with a floating-point exception inside this code. Reported-by: halfdog Tested-by: Borislav Petkov Link: http://lkml.kernel.org/r/CA%2B55aFxQnY_PCG_n4=0w-VG=YLXL-yr7oMxyy0WU2gCBAf3ydg@mail.gmail.com Signed-off-by: H. Peter Anvin (cherry picked from commit 26bef1318adc1b3a530ecc807ef99346db2aa8b0) [wt: in 2.6.32, patch applies to arch/x86/include/asm/i387.h. There's no static_cpu_has() so we use boot_cpu_has() like other kernels do with gcc3. ] Signed-off-by: Willy Tarreau --- arch/x86/include/asm/i387.h | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h index 0b20bbb..cb42fad 100644 --- a/arch/x86/include/asm/i387.h +++ b/arch/x86/include/asm/i387.h @@ -242,12 +242,13 @@ clear_state: /* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception is pending. Clear the x87 state here by setting it to fixed values. safe_address is a random variable that should be in L1 */ - alternative_input( - GENERIC_NOP8 GENERIC_NOP2, - "emms\n\t" /* clear stack tags */ - "fildl %[addr]", /* set F?P to defined value */ - X86_FEATURE_FXSAVE_LEAK, - [addr] "m" (safe_address)); + if (unlikely(boot_cpu_has(X86_FEATURE_FXSAVE_LEAK))) { + asm volatile( + "fnclex\n\t" + "emms\n\t" + "fildl %[addr]" /* set F?P to defined value */ + : : [addr] "m" (safe_address)); + } end: task_thread_info(tsk)->status &= ~TS_USEDFPU; } -- 1.7.12.2.21.g234cd45.dirty