From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-20.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1DEECC07E9D for ; Mon, 19 Jul 2021 16:28:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0367561629 for ; Mon, 19 Jul 2021 16:28:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241006AbhGSPrj (ORCPT ); Mon, 19 Jul 2021 11:47:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:44952 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349456AbhGSPpH (ORCPT ); Mon, 19 Jul 2021 11:45:07 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id E03C960E0C; Mon, 19 Jul 2021 16:25:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626711904; bh=p/JTXm9wsrfU7GIam4K9w3soNMbCZ9xOSYuMwZZMedE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dxPo24VhwTbkzSk03L/Y6HOcomIWSq+J90Vyiw83Hn2wptKU7Bc7INrkKHvfWfAUs a+H0hF8lpUV4yCw92zF9OjBzhjZwCBY7ieOfp+rJAvQRySOXMmzYJjDNS6ayL2znNx chbCo1rkO/EdGKtPA9PVfQaFzqQpRmsjsDKQnjbg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Florian Weimer , Jann Horn , Andy Lutomirski , "Chang S. Bae" , Borislav Petkov , Len Brown , Thomas Gleixner , Sasha Levin Subject: [PATCH 5.12 175/292] x86/signal: Detect and prevent an alternate signal stack overflow Date: Mon, 19 Jul 2021 16:53:57 +0200 Message-Id: <20210719144948.253461307@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210719144942.514164272@linuxfoundation.org> References: <20210719144942.514164272@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Chang S. Bae [ Upstream commit 2beb4a53fc3f1081cedc1c1a198c7f56cc4fc60c ] The kernel pushes context on to the userspace stack to prepare for the user's signal handler. When the user has supplied an alternate signal stack, via sigaltstack(2), it is easy for the kernel to verify that the stack size is sufficient for the current hardware context. Check if writing the hardware context to the alternate stack will exceed it's size. If yes, then instead of corrupting user-data and proceeding with the original signal handler, an immediate SIGSEGV signal is delivered. Refactor the stack pointer check code from on_sig_stack() and use the new helper. While the kernel allows new source code to discover and use a sufficient alternate signal stack size, this check is still necessary to protect binaries with insufficient alternate signal stack size from data corruption. Fixes: c2bc11f10a39 ("x86, AVX-512: Enable AVX-512 States Context Switch") Reported-by: Florian Weimer Suggested-by: Jann Horn Suggested-by: Andy Lutomirski Signed-off-by: Chang S. Bae Signed-off-by: Borislav Petkov Reviewed-by: Len Brown Acked-by: Thomas Gleixner Link: https://lkml.kernel.org/r/20210518200320.17239-6-chang.seok.bae@intel.com Link: https://bugzilla.kernel.org/show_bug.cgi?id=153531 Signed-off-by: Sasha Levin --- arch/x86/kernel/signal.c | 24 ++++++++++++++++++++---- include/linux/sched/signal.h | 19 ++++++++++++------- 2 files changed, 32 insertions(+), 11 deletions(-) diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index f306e85a08a6..6f4e261071e0 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -234,10 +234,11 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, void __user **fpstate) { /* Default to using normal stack */ + bool nested_altstack = on_sig_stack(regs->sp); + bool entering_altstack = false; unsigned long math_size = 0; unsigned long sp = regs->sp; unsigned long buf_fx = 0; - int onsigstack = on_sig_stack(sp); int ret; /* redzone */ @@ -246,15 +247,23 @@ 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) + /* + * This checks nested_altstack via sas_ss_flags(). Sensible + * programs use SS_AUTODISARM, which disables that check, and + * programs that don't use SS_AUTODISARM get compatible. + */ + if (sas_ss_flags(sp) == 0) { sp = current->sas_ss_sp + current->sas_ss_size; + entering_altstack = true; + } } else if (IS_ENABLED(CONFIG_X86_32) && - !onsigstack && + !nested_altstack && regs->ss != __USER_DS && !(ka->sa.sa_flags & SA_RESTORER) && ka->sa.sa_restorer) { /* This is the legacy signal stack switching. */ sp = (unsigned long) ka->sa.sa_restorer; + entering_altstack = true; } sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32), @@ -267,8 +276,15 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, * If we are on the alternate signal stack and would overflow it, don't. * Return an always-bogus address instead so we will die with SIGSEGV. */ - if (onsigstack && !likely(on_sig_stack(sp))) + if (unlikely((nested_altstack || entering_altstack) && + !__on_sig_stack(sp))) { + + if (show_unhandled_signals && printk_ratelimit()) + pr_info("%s[%d] overflowed sigaltstack\n", + current->comm, task_pid_nr(current)); + return (void __user *)-1L; + } /* save i387 and extended state */ ret = copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size); diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 3f6a0fcaa10c..ae60f838ebb9 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -537,6 +537,17 @@ static inline int kill_cad_pid(int sig, int priv) #define SEND_SIG_NOINFO ((struct kernel_siginfo *) 0) #define SEND_SIG_PRIV ((struct kernel_siginfo *) 1) +static inline int __on_sig_stack(unsigned long sp) +{ +#ifdef CONFIG_STACK_GROWSUP + return sp >= current->sas_ss_sp && + sp - current->sas_ss_sp < current->sas_ss_size; +#else + return sp > current->sas_ss_sp && + sp - current->sas_ss_sp <= current->sas_ss_size; +#endif +} + /* * True if we are on the alternate signal stack. */ @@ -554,13 +565,7 @@ static inline int on_sig_stack(unsigned long sp) if (current->sas_ss_flags & SS_AUTODISARM) return 0; -#ifdef CONFIG_STACK_GROWSUP - return sp >= current->sas_ss_sp && - sp - current->sas_ss_sp < current->sas_ss_size; -#else - return sp > current->sas_ss_sp && - sp - current->sas_ss_sp <= current->sas_ss_size; -#endif + return __on_sig_stack(sp); } static inline int sas_ss_flags(unsigned long sp) -- 2.30.2