From patchwork Thu Nov 19 19:02:36 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Chang S. Bae" X-Patchwork-Id: 41135 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 3703139ACC47; Thu, 19 Nov 2020 19:07:09 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 3703139ACC47 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1605812829; bh=l9fMe2WYwxUuEMNrOBUHF9ClED7zmzSq383rPc8L1dg=; h=To:Subject:Date:In-Reply-To:References:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=Z/ZAoiqw0pGFWWVuwxfXzqhTR0YWKGBSHlJnt0mAshZLEez9WwpSkUJdaK7435Nsj 2CoDMVDJDqSwH5h46pRsGEZNuN5uoRjnCZyzKJMeMzOVEb1bbbhD1habJAlDpYFJMC jTl4ouHpi87qBJKpXZV9gjR7Qk7n9BdwbcMDGnXA= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by sourceware.org (Postfix) with ESMTPS id BD2713857804 for ; Thu, 19 Nov 2020 19:07:05 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org BD2713857804 IronPort-SDR: FhBPTSolg6OB8Jp8Xf7lPNfNq+q6y0kCZ90B8stRCD6m4R4uMQLT3deWfCoGd8HniS5/HcBQsu IFw42TZJsO2A== X-IronPort-AV: E=McAfee;i="6000,8403,9810"; a="170563949" X-IronPort-AV: E=Sophos;i="5.78,354,1599548400"; d="scan'208";a="170563949" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Nov 2020 11:06:40 -0800 IronPort-SDR: QvspKCblnMCzsL5wITYJlqCsyv5vaoj+VeSN8G8G3ANsVrt2oRyOfr/jIoEfE+Rm7qkyy7yfoR iAXOglYNV5mA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.78,354,1599548400"; d="scan'208";a="431333996" Received: from chang-linux-3.sc.intel.com ([172.25.66.175]) by fmsmga001.fm.intel.com with ESMTP; 19 Nov 2020 11:06:40 -0800 To: tglx@linutronix.de, mingo@kernel.org, bp@suse.de, luto@kernel.org, x86@kernel.org Subject: [PATCH v2 3/4] x86/signal: Prevent an alternate stack overflow before a signal delivery Date: Thu, 19 Nov 2020 11:02:36 -0800 Message-Id: <20201119190237.626-4-chang.seok.bae@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20201119190237.626-1-chang.seok.bae@intel.com> References: <20201119190237.626-1-chang.seok.bae@intel.com> X-Spam-Status: No, score=-10.6 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: "Chang S. Bae via Libc-alpha" From: "Chang S. Bae" Reply-To: "Chang S. Bae" Cc: linux-arch@vger.kernel.org, len.brown@intel.com, tony.luck@intel.com, libc-alpha@sourceware.org, ravi.v.shankar@intel.com, chang.seok.bae@intel.com, linux-kernel@vger.kernel.org, dave.hansen@intel.com, linux-api@vger.kernel.org, Dave.Martin@arm.com Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" The kernel pushes data on the userspace stack when entering a signal. If using a sigaltstack(), the kernel precisely knows the user stack size. When the kernel knows that the user stack is too small, avoid the overflow and do an immediate SIGSEGV instead. This overflow is known to occur on systems with large XSAVE state. The effort to increase the size typically used for altstacks reduces the frequency of these overflows, but this approach is still useful for legacy binaries. Here the kernel expects a bit conservative stack size (for 64-bit apps). Legacy binaries used a too-small sigaltstack would be already overflowed before this change, if they run on modern hardware. Signed-off-by: Chang S. Bae Reviewed-by: Len Brown Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org --- arch/x86/ia32/ia32_signal.c | 11 ++++++++--- arch/x86/include/asm/sigframe.h | 2 ++ arch/x86/kernel/signal.c | 16 +++++++++++++++- 3 files changed, 25 insertions(+), 4 deletions(-) diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 81cf22398cd1..85abd9eb79d5 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -210,13 +210,18 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs, sp = regs->sp; /* This is the X/Open sanctioned signal stack switching. */ - if (ksig->ka.sa.sa_flags & SA_ONSTACK) + if (ksig->ka.sa.sa_flags & SA_ONSTACK) { + /* If the altstack might overflow, die with SIGSEGV: */ + if (!altstack_size_ok(current)) + return (void __user *)-1L; + sp = sigsp(sp, ksig); /* This is the legacy signal stack switching. */ - else if (regs->ss != __USER32_DS && + } else if (regs->ss != __USER32_DS && !(ksig->ka.sa.sa_flags & SA_RESTORER) && - ksig->ka.sa.sa_restorer) + ksig->ka.sa.sa_restorer) { sp = (unsigned long) ksig->ka.sa.sa_restorer; + } sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size); *fpstate = (struct _fpstate_32 __user *) sp; diff --git a/arch/x86/include/asm/sigframe.h b/arch/x86/include/asm/sigframe.h index ac77f3f90bc9..c9f2f9ace76f 100644 --- a/arch/x86/include/asm/sigframe.h +++ b/arch/x86/include/asm/sigframe.h @@ -106,6 +106,8 @@ struct rt_sigframe_x32 { #define SIZEOF_rt_sigframe_x32 0 #endif +bool altstack_size_ok(struct task_struct *tsk); + void __init init_sigframe_size(void); #endif /* _ASM_X86_SIGFRAME_H */ diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index ee6f1ceaa7a2..cee41d684dc2 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -251,8 +251,13 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, /* This is the X/Open sanctioned signal stack switching. */ if (ka->sa.sa_flags & SA_ONSTACK) { - if (sas_ss_flags(sp) == 0) + if (sas_ss_flags(sp) == 0) { + /* If the altstack might overflow, die with SIGSEGV: */ + if (!altstack_size_ok(current)) + return (void __user *)-1L; + sp = current->sas_ss_sp + current->sas_ss_size; + } } else if (IS_ENABLED(CONFIG_X86_32) && !onsigstack && regs->ss != __USER_DS && @@ -725,6 +730,15 @@ unsigned long get_sigframe_size(void) return max_frame_size; } +bool altstack_size_ok(struct task_struct *tsk) +{ + /* + * Can this task's sigaltstack accommodate the largest + * signal frame the kernel might need? + */ + return (tsk->sas_ss_size >= max_frame_size); +} + static inline int is_ia32_compat_frame(struct ksignal *ksig) { return IS_ENABLED(CONFIG_IA32_EMULATION) &&