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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 03CF4C433E0 for ; Thu, 25 Mar 2021 16:21:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9D8F61A39 for ; Thu, 25 Mar 2021 16:21:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229614AbhCYQVX (ORCPT ); Thu, 25 Mar 2021 12:21:23 -0400 Received: from mx2.suse.de ([195.135.220.15]:33798 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229812AbhCYQUz (ORCPT ); Thu, 25 Mar 2021 12:20:55 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 72A48AA55; Thu, 25 Mar 2021 16:20:53 +0000 (UTC) Date: Thu, 25 Mar 2021 17:20:47 +0100 From: Borislav Petkov To: "Bae, Chang Seok" Cc: Thomas Gleixner , "mingo@kernel.org" , "luto@kernel.org" , "x86@kernel.org" , "Brown, Len" , "Hansen, Dave" , "hjl.tools@gmail.com" , "Dave.Martin@arm.com" , "jannh@google.com" , "mpe@ellerman.id.au" , "carlos@redhat.com" , "Luck, Tony" , "Shankar, Ravi V" , "libc-alpha@sourceware.org" , "linux-arch@vger.kernel.org" , "linux-api@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate signal stack overflow Message-ID: <20210325162047.GA32296@zn.tnic> References: <20210316065215.23768-1-chang.seok.bae@intel.com> <20210316065215.23768-6-chang.seok.bae@intel.com> <20210316115248.GB18822@zn.tnic> <16A53D65-2460-49B3-892B-81EF8D7B12B9@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <16A53D65-2460-49B3-892B-81EF8D7B12B9@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue, Mar 16, 2021 at 06:26:46PM +0000, Bae, Chang Seok wrote: > I suspect the AVX-512 states not enabled there. Ok, I found a machine which has AVX-512: [ 0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x020: 'AVX-512 opmask' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x040: 'AVX-512 Hi256' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x080: 'AVX-512 ZMM_Hi256' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x200: 'Protection Keys User registers' [ 0.000000] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256 [ 0.000000] x86/fpu: xstate_offset[5]: 832, xstate_sizes[5]: 64 [ 0.000000] x86/fpu: xstate_offset[6]: 896, xstate_sizes[6]: 512 [ 0.000000] x86/fpu: xstate_offset[7]: 1408, xstate_sizes[7]: 1024 [ 0.000000] x86/fpu: xstate_offset[9]: 2432, xstate_sizes[9]: 8 [ 0.000000] x86/fpu: Enabled xstate features 0x2e7, context size is 2440 bytes, using 'compacted' format. and applied your patch and added a debug printk, see end of mail. Then, I ran the test case: $ gcc tst-minsigstksz-2.c -DMY_MINSIGSTKSZ=3453 -o tst-minsigstksz-2 $ ./tst-minsigstksz-2 tst-minsigstksz-2: changed byte 50 bytes below configured stack Whoops. And the debug print said: [ 5395.252884] signal: get_sigframe: sp: 0x7f54ec39e7b8, sas_ss_sp: 0x7f54ec39e6ce, sas_ss_size 0xd7d which tells me that, AFAICT, your check whether we have enough alt stack doesn't seem to work in this case. Thx. diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index a06cb107c0e8..a7396f7c3832 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -237,7 +237,7 @@ 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 */ @@ -246,8 +246,11 @@ 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 && @@ -263,11 +266,16 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size, sp = align_sigframe(sp - frame_size); + if (onsigstack) + pr_info("%s: sp: 0x%lx, sas_ss_sp: 0x%lx, sas_ss_size 0x%lx\n", + __func__, sp, current->sas_ss_sp, current->sas_ss_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 (onsigstack && unlikely(sp <= current->sas_ss_sp || + sp - current->sas_ss_sp > current->sas_ss_size)) return (void __user *)-1L; /* save i387 and extended state */ -- Regards/Gruss, Boris. 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