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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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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 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 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 978f47c1-8c2e-4517-7fb6-08d963ee27d6 X-MS-Exchange-CrossTenant-AuthSource: SN6PR12MB2718.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Aug 2021 15:21:17.4089 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Yp8JXpW89gxpwi/NNey4QGih64BHBYpHwYeEUQId3PENXIvSmPdPqcUMwnzRq7bB5rjaRlN9c6YZGwQ+GBLAkg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR12MB4557 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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); }