From: Ard Biesheuvel Date: Thu, 28 Aug 2025 10:22:22 +0000 (+0200) Subject: x86/boot: Create a confined code area for startup code X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=7b38dec3c5af54665a4b29483aa02bd1c1e71cf1;p=thirdparty%2Fkernel%2Fstable.git x86/boot: Create a confined code area for startup code In order to be able to have tight control over which code may execute from the early 1:1 mapping of memory, but still link vmlinux as a single executable, prefix all symbol references in startup code with __pi_, and invoke it from outside using the __pi_ prefix. Use objtool to check that no absolute symbol references are present in the startup code, as these cannot be used from code running from the 1:1 mapping. Note that this also requires disabling the latent-entropy GCC plugin, as the global symbol references that it injects would require explicit exports, and given that the startup code rarely executes more than once, it is not a useful source of entropy anyway. Signed-off-by: Ard Biesheuvel Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/20250828102202.1849035-43-ardb+git@google.com --- diff --git a/arch/x86/boot/startup/Makefile b/arch/x86/boot/startup/Makefile index 32737f4ab5a80..e8fdf020b4223 100644 --- a/arch/x86/boot/startup/Makefile +++ b/arch/x86/boot/startup/Makefile @@ -4,6 +4,7 @@ KBUILD_AFLAGS += -D__DISABLE_EXPORTS KBUILD_CFLAGS += -D__DISABLE_EXPORTS -mcmodel=small -fPIC \ -Os -DDISABLE_BRANCH_PROFILING \ $(DISABLE_STACKLEAK_PLUGIN) \ + $(DISABLE_LATENT_ENTROPY_PLUGIN) \ -fno-stack-protector -D__NO_FORTIFY \ -fno-jump-tables \ -include $(srctree)/include/linux/hidden.h @@ -36,3 +37,16 @@ $(patsubst %.o,$(obj)/%.o,$(lib-y)): OBJECT_FILES_NON_STANDARD := y # $(pi-objs): objtool-enabled = 1 $(pi-objs): objtool-args = $(if $(delay-objtool),,$(objtool-args-y)) --noabs + +# +# Confine the startup code by prefixing all symbols with __pi_ (for position +# independent). This ensures that startup code can only call other startup +# code, or code that has explicitly been made accessible to it via a symbol +# alias. +# +$(obj)/%.pi.o: OBJCOPYFLAGS := --prefix-symbols=__pi_ +$(obj)/%.pi.o: $(obj)/%.o FORCE + $(call if_changed,objcopy) + +targets += $(obj-y) +obj-y := $(patsubst %.o,%.pi.o,$(obj-y)) diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev-shared.c index 2a28463edd996..e09c66845e43e 100644 --- a/arch/x86/boot/startup/sev-shared.c +++ b/arch/x86/boot/startup/sev-shared.c @@ -12,7 +12,6 @@ #include #ifndef __BOOT_COMPRESSED -#define error(v) pr_err(v) #define has_cpuflag(f) boot_cpu_has(f) #else #undef WARN diff --git a/arch/x86/boot/startup/sme.c b/arch/x86/boot/startup/sme.c index bf9153b9a3d9f..52b98e7624fe8 100644 --- a/arch/x86/boot/startup/sme.c +++ b/arch/x86/boot/startup/sme.c @@ -568,7 +568,6 @@ void __head sme_enable(struct boot_params *bp) #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION /* Local version for startup code, which never operates on user page tables */ -__weak pgd_t __pti_set_user_pgtbl(pgd_t *pgdp, pgd_t pgd) { return pgd; diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c index b9133c825f90c..cf9a511b47e09 100644 --- a/arch/x86/coco/sev/core.c +++ b/arch/x86/coco/sev/core.c @@ -272,7 +272,7 @@ static int svsm_perform_call_protocol(struct svsm_call *call) do { ret = ghcb ? svsm_perform_ghcb_protocol(ghcb, call) - : svsm_perform_msr_protocol(call); + : __pi_svsm_perform_msr_protocol(call); } while (ret == -EAGAIN); if (sev_cfg.ghcbs_initialized) diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h index 692af46603a17..914eb32581c73 100644 --- a/arch/x86/include/asm/setup.h +++ b/arch/x86/include/asm/setup.h @@ -53,6 +53,7 @@ extern void i386_reserve_resources(void); extern unsigned long __startup_64(unsigned long p2v_offset, struct boot_params *bp); extern void startup_64_setup_gdt_idt(void); extern void startup_64_load_idt(void *vc_handler); +extern void __pi_startup_64_load_idt(void *vc_handler); extern void early_setup_idt(void); extern void __init do_early_exception(struct pt_regs *regs, int trapnr); diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index 0030c7125b291..f222bef9dca88 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h @@ -551,6 +551,7 @@ struct cpuid_leaf { }; int svsm_perform_msr_protocol(struct svsm_call *call); +int __pi_svsm_perform_msr_protocol(struct svsm_call *call); int snp_cpuid(void (*cpuid_fn)(void *ctx, struct cpuid_leaf *leaf), void *ctx, struct cpuid_leaf *leaf); diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 1bc40d0785ee3..fd28b53dbac51 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -319,5 +319,5 @@ void early_setup_idt(void) handler = vc_boot_ghcb; } - startup_64_load_idt(handler); + __pi_startup_64_load_idt(handler); } diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 3e9b3a3bd0396..d219963ecb605 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -71,7 +71,7 @@ SYM_CODE_START_NOALIGN(startup_64) xorl %edx, %edx wrmsr - call startup_64_setup_gdt_idt + call __pi_startup_64_setup_gdt_idt /* Now switch to __KERNEL_CS so IRET works reliably */ pushq $__KERNEL_CS @@ -91,7 +91,7 @@ SYM_CODE_START_NOALIGN(startup_64) * subsequent code. Pass the boot_params pointer as the first argument. */ movq %r15, %rdi - call sme_enable + call __pi_sme_enable #endif /* Sanitize CPU configuration */ @@ -111,7 +111,7 @@ SYM_CODE_START_NOALIGN(startup_64) * programmed into CR3. */ movq %r15, %rsi - call __startup_64 + call __pi___startup_64 /* Form the CR3 value being sure to include the CR3 modifier */ leaq early_top_pgt(%rip), %rcx @@ -562,7 +562,7 @@ SYM_CODE_START_NOALIGN(vc_no_ghcb) /* Call C handler */ movq %rsp, %rdi movq ORIG_RAX(%rsp), %rsi - call do_vc_no_ghcb + call __pi_do_vc_no_ghcb /* Unwind pt_regs */ POP_REGS diff --git a/arch/x86/mm/mem_encrypt_boot.S b/arch/x86/mm/mem_encrypt_boot.S index f8a33b25ae869..edbf9c9988484 100644 --- a/arch/x86/mm/mem_encrypt_boot.S +++ b/arch/x86/mm/mem_encrypt_boot.S @@ -16,7 +16,7 @@ .text .code64 -SYM_FUNC_START(sme_encrypt_execute) +SYM_FUNC_START(__pi_sme_encrypt_execute) /* * Entry parameters: @@ -69,9 +69,9 @@ SYM_FUNC_START(sme_encrypt_execute) ANNOTATE_UNRET_SAFE ret int3 -SYM_FUNC_END(sme_encrypt_execute) +SYM_FUNC_END(__pi_sme_encrypt_execute) -SYM_FUNC_START(__enc_copy) +SYM_FUNC_START_LOCAL(__enc_copy) ANNOTATE_NOENDBR /* * Routine used to encrypt memory in place. diff --git a/tools/objtool/check.c b/tools/objtool/check.c index fb47327075fba..d0d20666e8727 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -3564,7 +3564,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, if (func && insn_func(insn) && func != insn_func(insn)->pfunc) { /* Ignore KCFI type preambles, which always fall through */ if (!strncmp(func->name, "__cfi_", 6) || - !strncmp(func->name, "__pfx_", 6)) + !strncmp(func->name, "__pfx_", 6) || + !strncmp(func->name, "__pi___pfx_", 11)) return 0; if (file->ignore_unreachables)