From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by sourceware.org (Postfix) with ESMTPS id 7675D382D831 for ; Wed, 23 Dec 2020 01:57:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 7675D382D831 IronPort-SDR: kNZM54zNg22amh0X39uiRJ/A4hZJIFz8gDp4MCi/ksNgxaA4LpZd6ai6b07hynrzRQUXB9E2kd /xXFRvSR+DSA== X-IronPort-AV: E=McAfee;i="6000,8403,9843"; a="194393141" X-IronPort-AV: E=Sophos;i="5.78,440,1599548400"; d="scan'208";a="194393141" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Dec 2020 17:57:39 -0800 IronPort-SDR: 2iC4ku/AQH/vA/7CKujV/e6uES2g8t+A54AKTmW/yAhBKhPS2diVEsV7ahGjj8Mw0pzqrXBp87 baQzAs0ovHjQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.78,440,1599548400"; d="scan'208";a="457755742" Received: from chang-linux-3.sc.intel.com ([172.25.66.175]) by fmsmga001.fm.intel.com with ESMTP; 22 Dec 2020 17:57:39 -0800 From: "Chang S. Bae" To: bp@suse.de, tglx@linutronix.de, mingo@kernel.org, luto@kernel.org, x86@kernel.org Cc: len.brown@intel.com, dave.hansen@intel.com, hjl.tools@gmail.com, Dave.Martin@arm.com, jannh@google.com, mpe@ellerman.id.au, tony.luck@intel.com, ravi.v.shankar@intel.com, libc-alpha@sourceware.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, chang.seok.bae@intel.com Subject: [PATCH v3 3/4] x86/signal: Prevent an alternate stack overflow before a signal delivery Date: Tue, 22 Dec 2020 17:53:11 -0800 Message-Id: <20201223015312.4882-4-chang.seok.bae@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20201223015312.4882-1-chang.seok.bae@intel.com> References: <20201223015312.4882-1-chang.seok.bae@intel.com> X-Spam-Status: No, score=-10.7 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, 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-List-Received-Date: Wed, 23 Dec 2020 01:57:41 -0000 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. Suggested-by: Jann Horn Signed-off-by: Chang S. Bae Reviewed-by: Len Brown Cc: Jann Horn Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org --- Changes from v2: * Simplified the implementation (Jann Horn) --- arch/x86/kernel/signal.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 761d856f8ef7..91056a940271 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -242,7 +242,7 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, unsigned long math_size = 0; unsigned long sp = regs->sp; unsigned long buf_fx = 0; - int onsigstack = on_sig_stack(sp); + bool onsigstack = on_sig_stack(sp); int ret; /* redzone */ @@ -251,8 +251,11 @@ 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) { sp = current->sas_ss_sp + current->sas_ss_size; + /* On the alternate signal stack */ + onsigstack = true; + } } else if (IS_ENABLED(CONFIG_X86_32) && !onsigstack && regs->ss != __USER_DS && -- 2.17.1