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David Alan Gilbert" , , , , , Brijesh Singh Subject: [PATCH v12 23/46] x86/head/64: Re-enable stack protection Date: Mon, 7 Mar 2022 15:33:33 -0600 Message-ID: <20220307213356.2797205-24-brijesh.singh@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220307213356.2797205-1-brijesh.singh@amd.com> References: <20220307213356.2797205-1-brijesh.singh@amd.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: ed9d8c91-9c8b-4073-c4a0-08da00825560 X-MS-TrafficTypeDiagnostic: MN2PR12MB3117:EE_ X-Microsoft-Antispam-PRVS: X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230001)(4636009)(36840700001)(40470700004)(46966006)(40460700003)(7406005)(54906003)(8676002)(5660300002)(110136005)(8936002)(2616005)(186003)(316002)(16526019)(1076003)(81166007)(356005)(26005)(36756003)(7416002)(70586007)(70206006)(508600001)(6666004)(82310400004)(36860700001)(44832011)(47076005)(4326008)(86362001)(83380400001)(336012)(2906002)(426003)(7696005)(36900700001)(2101003);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Mar 2022 21:35:00.3718 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ed9d8c91-9c8b-4073-c4a0-08da00825560 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT031.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB3117 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Michael Roth Due to commit 103a4908ad4d ("x86/head/64: Disable stack protection for head$(BITS).o"), kernel/head{32,64}.c are 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, there may still be issues with calls 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, re-enable stack protection for head32.c/head64.c, and make the appropriate changes to ensure the segment used for the stack canary is initialized in advance of any stack-protected C calls. For head64.c: - The BSP will enter from startup_64() and call into C code (startup_64_setup_env()) shortly after setting up the stack, which may result in calls to stack-protected code. Set up %gs early to allow for this safely. - APs will enter from secondary_startup_64*(), and %gs will be set up soon after. There is one call to C code prior to %gs being setup (__startup_secondary_64()), but it is only to fetch 'sme_me_mask' global, so just load 'sme_me_mask' directly instead, and remove the now-unused __startup_secondary_64() function. For head32.c: - BSPs/APs will set %fs to __BOOT_DS prior to any C calls. In recent kernels, the compiler is configured to access the stack canary at %fs:__stack_chk_guard [1], which overlaps with the initial per-cpu '__stack_chk_guard' variable in the initial/"master" .data..percpu area. This is sufficient to allow access to the canary for use during initial startup, so no changes are needed there. [1] commit 3fb0fdb3bbe7 ("x86/stackprotector/32: Make the canary into a regular percpu variable") Suggested-by: Joerg Roedel #for 64-bit %gs set up Signed-off-by: Michael Roth Signed-off-by: Brijesh Singh --- arch/x86/include/asm/setup.h | 1 - arch/x86/kernel/Makefile | 2 -- arch/x86/kernel/head64.c | 9 --------- arch/x86/kernel/head_64.S | 24 +++++++++++++++++++++--- 4 files changed, 21 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h index a12458a7a8d4..72ede9159951 100644 --- a/arch/x86/include/asm/setup.h +++ b/arch/x86/include/asm/setup.h @@ -49,7 +49,6 @@ extern unsigned long saved_video_mode; extern void reserve_standard_io_resources(void); extern void i386_reserve_resources(void); extern unsigned long __startup_64(unsigned long physaddr, struct boot_params *bp); -extern unsigned long __startup_secondary_64(void); extern void startup_64_setup_env(unsigned long physbase); extern void early_setup_idt(void); extern void __init do_early_exception(struct pt_regs *regs, int trapnr); diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 6462e3dd98f4..ff4da5784d63 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -46,8 +46,6 @@ endif # non-deterministic coverage. KCOV_INSTRUMENT := n -CFLAGS_head$(BITS).o += -fno-stack-protector - CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace obj-y := process_$(BITS).o signal.o diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 656d2f3e2cf0..c185f4831498 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -318,15 +318,6 @@ unsigned long __head __startup_64(unsigned long physaddr, return sme_postprocess_startup(bp, pmd); } -unsigned long __startup_secondary_64(void) -{ - /* - * Return the SME encryption mask (if SME is active) to be used as a - * modifier for the initial pgdir entry programmed into CR3. - */ - return sme_get_me_mask(); -} - /* Wipe all early page tables except for the kernel symbol map */ static void __init reset_early_page_tables(void) { diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 9c2c3aff5ee4..9e84263bcb94 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -65,6 +65,22 @@ SYM_CODE_START_NOALIGN(startup_64) leaq (__end_init_task - FRAME_SIZE)(%rip), %rsp leaq _text(%rip), %rdi + + /* + * initial_gs points to initial fixed_percpu_data struct with storage for + * the stack protector canary. Global pointer fixups are needed at this + * stage, so apply them as is done in fixup_pointer(), and initialize %gs + * such that the canary can be accessed at %gs:40 for subsequent C calls. + */ + movl $MSR_GS_BASE, %ecx + movq initial_gs(%rip), %rax + movq $_text, %rdx + subq %rdx, %rax + addq %rdi, %rax + movq %rax, %rdx + shrq $32, %rdx + wrmsr + pushq %rsi call startup_64_setup_env popq %rsi @@ -145,9 +161,11 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) * Retrieve the modifier (SME encryption mask if SME is active) to be * added to the initial pgdir entry that will be programmed into CR3. */ - pushq %rsi - call __startup_secondary_64 - popq %rsi +#ifdef CONFIG_AMD_MEM_ENCRYPT + movq sme_me_mask, %rax +#else + xorq %rax, %rax +#endif /* Form the CR3 value being sure to include the CR3 modifier */ addq $(init_top_pgt - __START_KERNEL_map), %rax -- 2.25.1