From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934649AbbLPRvC (ORCPT ); Wed, 16 Dec 2015 12:51:02 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:50102 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966662AbbLPRkt (ORCPT ); Wed, 16 Dec 2015 12:40:49 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Dave Hansen , Andy Lutomirski , Borislav Petkov , Brian Gerst , Denys Vlasenko , "H. Peter Anvin" , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , dave@sr71.net, fenghua.yu@intel.com, yu-cheng.yu@intel.com, Ingo Molnar , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 010/128] x86/fpu: Fix 32-bit signal frame handling Date: Wed, 16 Dec 2015 09:37:30 -0800 Message-Id: <1450287568-19808-11-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1450287568-19808-1-git-send-email-kamal@canonical.com> References: <1450287568-19808-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.19.8-ckt12 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Dave Hansen commit ab6b52947545a5355154f64f449f97af9d05845f upstream. (This should have gone to LKML originally. Sorry for the extra noise, folks on the cc.) Background: Signal frames on x86 have two formats: 1. For 32-bit executables (whether on a real 32-bit kernel or under 32-bit emulation on a 64-bit kernel) we have a 'fpregset_t' that includes the "FSAVE" registers. 2. For 64-bit executables (on 64-bit kernels obviously), the 'fpregset_t' is smaller and does not contain the "FSAVE" state. When creating the signal frame, we have to be aware of whether we are running a 32 or 64-bit executable so we create the correct format signal frame. Problem: save_xstate_epilog() uses 'fx_sw_reserved_ia32' whenever it is called for a 32-bit executable. This is for real 32-bit and ia32 emulation. But, fpu__init_prepare_fx_sw_frame() only initializes 'fx_sw_reserved_ia32' when emulation is enabled, *NOT* for real 32-bit kernels. This leads to really wierd situations where 32-bit programs lose their extended state when returning from a signal handler. The kernel copies the uninitialized (zero) 'fx_sw_reserved_ia32' out to userspace in save_xstate_epilog(). But when returning from the signal, the kernel errors out in check_for_xstate() when it does not see FP_XSTATE_MAGIC1 present (because it was zeroed). This leads to the FPU/XSAVE state being initialized. For MPX, this leads to the most permissive state and means we silently lose bounds violations. I think this would also mean that we could lose *ANY* FPU/SSE/AVX state. I'm not sure why no one has spotted this bug. I believe this was broken by: 72a671ced66d ("x86, fpu: Unify signal handling code paths for x86 and x86_64 kernels") way back in 2012. Signed-off-by: Dave Hansen Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dave@sr71.net Cc: fenghua.yu@intel.com Cc: yu-cheng.yu@intel.com Link: http://lkml.kernel.org/r/20151111002354.A0799571@viggo.jf.intel.com Signed-off-by: Ingo Molnar [ kamal: backport to 3.19-stable: applied to kernel/xsave.c; context ] Signed-off-by: Kamal Mostafa --- arch/x86/kernel/xsave.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c index 8be1e17..8c2b709 100644 --- a/arch/x86/kernel/xsave.c +++ b/arch/x86/kernel/xsave.c @@ -432,20 +432,19 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size) */ static void prepare_fx_sw_frame(void) { - int fsave_header_size = sizeof(struct i387_fsave_struct); int size = xstate_size + FP_XSTATE_MAGIC2_SIZE; - if (config_enabled(CONFIG_X86_32)) - size += fsave_header_size; - fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1; fx_sw_reserved.extended_size = size; fx_sw_reserved.xstate_bv = pcntxt_mask; fx_sw_reserved.xstate_size = xstate_size; - if (config_enabled(CONFIG_IA32_EMULATION)) { + if (config_enabled(CONFIG_IA32_EMULATION) || + config_enabled(CONFIG_X86_32)) { + int fsave_header_size = sizeof(struct i387_fsave_struct); + fx_sw_reserved_ia32 = fx_sw_reserved; - fx_sw_reserved_ia32.extended_size += fsave_header_size; + fx_sw_reserved_ia32.extended_size = size + fsave_header_size; } } -- 1.9.1