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Shutemov" , Andi Kleen , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com, Brijesh Singh Subject: [PATCH Part1 v5 23/38] x86/head/64: set up a startup %gs for stack protector Date: Fri, 20 Aug 2021 10:19:18 -0500 Message-Id: <20210820151933.22401-24-brijesh.singh@amd.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210820151933.22401-1-brijesh.singh@amd.com> References: <20210820151933.22401-1-brijesh.singh@amd.com> X-ClientProxiedBy: SA9P223CA0002.NAMP223.PROD.OUTLOOK.COM (2603:10b6:806:26::7) To SN6PR12MB2718.namprd12.prod.outlook.com (2603:10b6:805:6f::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from sbrijesh-desktop.amd.com (165.204.77.1) by SA9P223CA0002.NAMP223.PROD.OUTLOOK.COM (2603:10b6:806:26::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4436.19 via Frontend Transport; Fri, 20 Aug 2021 15:21:16 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 978f47c1-8c2e-4517-7fb6-08d963ee27d6 X-MS-TrafficTypeDiagnostic: SA0PR12MB4557: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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dkim=pass header.d=amd.com header.s=selector1 header.b="vCJ6P/yO"; dmarc=pass (policy=quarantine) header.from=amd.com; spf=pass (imf30.hostedemail.com: domain of brijesh.singh@amd.com designates 40.107.100.49 as permitted sender) smtp.mailfrom=brijesh.singh@amd.com X-HE-Tag: 1629472879-246930 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Michael Roth As of commit 103a4908ad4d ("x86/head/64: Disable stack protection for head$(BITS).o") kernel/head64.c is compiled with -fno-stack-protector to allow a call to set_bringup_idt_handler(), which would otherwise have stack protection enabled with CONFIG_STACKPROTECTOR_STRONG. While sufficient for that case, this will still cause issues if we attempt to call out to any external functions that were compiled with stack protection enabled that in-turn make stack-protected calls, or if the exception handlers set up by set_bringup_idt_handler() make calls to stack-protected functions. Subsequent patches for SEV-SNP CPUID validation support will introduce both such cases. Attempting to disable stack protection for everything in scope to address that is prohibitive since much of the code, like SEV-ES #VC handler, is shared code that remains in use after boot and could benefit from having stack protection enabled. Attempting to inline calls is brittle and can quickly balloon out to library/helper code where that's not really an option. Instead, set up %gs to point a buffer that stack protector can use for canary values when needed. In doing so, it's likely we can stop using -no-stack-protector for head64.c, but that hasn't been tested yet, and head32.c would need a similar solution to be safe, so that is left as a potential follow-up. Signed-off-by: Michael Roth Signed-off-by: Brijesh Singh --- arch/x86/kernel/Makefile | 2 +- arch/x86/kernel/head64.c | 20 ++++++++++++++++++++ 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 3e625c61f008..5abdfd0dbbc3 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -46,7 +46,7 @@ endif # non-deterministic coverage. KCOV_INSTRUMENT := n -CFLAGS_head$(BITS).o += -fno-stack-protector +CFLAGS_head32.o += -fno-stack-protector CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index a1711c4594fa..f1b76a54c84e 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -74,6 +74,11 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = { [GDT_ENTRY_KERNEL_DS] = GDT_ENTRY_INIT(0xc093, 0, 0xfffff), }; +/* For use by stack protector code before switching to virtual addresses */ +#if CONFIG_STACKPROTECTOR +static char startup_gs_area[64]; +#endif + /* * Address needs to be set at runtime because it references the startup_gdt * while the kernel still uses a direct mapping. @@ -605,6 +610,8 @@ void early_setup_idt(void) */ void __head startup_64_setup_env(unsigned long physbase) { + u64 gs_area = (u64)fixup_pointer(startup_gs_area, physbase); + /* Load GDT */ startup_gdt_descr.address = (unsigned long)fixup_pointer(startup_gdt, physbase); native_load_gdt(&startup_gdt_descr); @@ -614,5 +621,18 @@ void __head startup_64_setup_env(unsigned long physbase) "movl %%eax, %%ss\n" "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory"); + /* + * GCC stack protection needs a place to store canary values. The + * default is %gs:0x28, which is what the kernel currently uses. + * Point GS base to a buffer that can be used for this purpose. + * Note that newer GCCs now allow this location to be configured, + * so if we change from the default in the future we need to ensure + * that this buffer overlaps whatever address ends up being used. + */ +#if CONFIG_STACKPROTECTOR + asm volatile("movl %%eax, %%gs\n" : : "a"(__KERNEL_DS) : "memory"); + native_wrmsr(MSR_GS_BASE, gs_area, gs_area >> 32); +#endif + startup_64_load_idt(physbase); }