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Thu, 28 Aug 2025 03:22:56 -0700 (PDT) Date: Thu, 28 Aug 2025 12:22:22 +0200 In-Reply-To: <20250828102202.1849035-24-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250828102202.1849035-24-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=7681; i=ardb@kernel.org; h=from:subject; bh=M8ezlf5/PDz1F/7JZ4xezbsg4QahoU+ms5tGuByspuE=; b=owGbwMvMwCVmkMcZplerG8N4Wi2JIWOD7kPW0yoVrRUXrzImbau8tVh/14+rC0TSPqSHMJZM4 J2m7NDXUcrCIMbFICumyCIw+++7nacnStU6z5KFmcPKBDKEgYtTACay/isjww+1p/t/3u21176w bO7xw2HZF0zzj/E8rc98XtEkP1OT/xbD/+i0utu7/uikbZReVzPHWTrxztRCwcOpDg55134nSEZ e4wcA X-Mailer: git-send-email 2.51.0.268.g9569e192d0-goog Message-ID: <20250828102202.1849035-43-ardb+git@google.com> Subject: [PATCH v7 19/22] x86/boot: Create a confined code area for startup code From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: linux-efi@vger.kernel.org, x86@kernel.org, Ard Biesheuvel , Borislav Petkov , Ingo Molnar , Kevin Loughlin , Tom Lendacky , Josh Poimboeuf , Peter Zijlstra , Nikunj A Dadhania Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel 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 --- arch/x86/boot/startup/Makefile | 14 ++++++++++++++ arch/x86/boot/startup/sev-shared.c | 1 - arch/x86/boot/startup/sme.c | 1 - arch/x86/coco/sev/core.c | 2 +- arch/x86/include/asm/setup.h | 1 + arch/x86/include/asm/sev.h | 1 + arch/x86/kernel/head64.c | 2 +- arch/x86/kernel/head_64.S | 8 ++++---- arch/x86/mm/mem_encrypt_boot.S | 6 +++--- tools/objtool/check.c | 3 ++- 10 files changed, 27 insertions(+), 12 deletions(-) diff --git a/arch/x86/boot/startup/Makefile b/arch/x86/boot/startup/Makefile index 32737f4ab5a8..e8fdf020b422 100644 --- a/arch/x86/boot/startup/Makefile +++ b/arch/x86/boot/startup/Makefile @@ -4,6 +4,7 @@ KBUILD_AFLAGS +=3D -D__DISABLE_EXPORTS KBUILD_CFLAGS +=3D -D__DISABLE_EXPORTS -mcmodel=3Dsmall -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_ST= ANDARD :=3D y # $(pi-objs): objtool-enabled =3D 1 $(pi-objs): objtool-args =3D $(if $(delay-objtool),,$(objtool-args-y)) --n= oabs + +# +# Confine the startup code by prefixing all symbols with __pi_ (for positi= on +# 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. +# +$(obj)/%.pi.o: OBJCOPYFLAGS :=3D --prefix-symbols=3D__pi_ +$(obj)/%.pi.o: $(obj)/%.o FORCE + $(call if_changed,objcopy) + +targets +=3D $(obj-y) +obj-y :=3D $(patsubst %.o,%.pi.o,$(obj-y)) diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev= -shared.c index 180f54570022..d6d807da2e6e 100644 --- a/arch/x86/boot/startup/sev-shared.c +++ b/arch/x86/boot/startup/sev-shared.c @@ -12,7 +12,6 @@ #include =20 #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 70ea1748c0a7..eb6a758ba660 100644 --- a/arch/x86/boot/startup/sme.c +++ b/arch/x86/boot/startup/sme.c @@ -567,7 +567,6 @@ void __head sme_enable(struct boot_params *bp) =20 #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION /* Local version for startup code, which never operates on user page table= s */ -__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 b9133c825f90..cf9a511b47e0 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) =20 do { ret =3D ghcb ? svsm_perform_ghcb_protocol(ghcb, call) - : svsm_perform_msr_protocol(call); + : __pi_svsm_perform_msr_protocol(call); } while (ret =3D=3D -EAGAIN); =20 if (sev_cfg.ghcbs_initialized) diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h index 692af46603a1..914eb32581c7 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_pa= rams *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); =20 diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index 416715aaadf7..d3f0f17834fa 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h @@ -551,6 +551,7 @@ struct cpuid_leaf { }; =20 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); =20 diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 1bc40d0785ee..fd28b53dbac5 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -319,5 +319,5 @@ void early_setup_idt(void) handler =3D vc_boot_ghcb; } =20 - 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 3e9b3a3bd039..d219963ecb60 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 =20 - call startup_64_setup_gdt_idt + call __pi_startup_64_setup_gdt_idt =20 /* 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 =20 /* 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 =20 /* 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 =20 /* Unwind pt_regs */ POP_REGS diff --git a/arch/x86/mm/mem_encrypt_boot.S b/arch/x86/mm/mem_encrypt_boot.S index f8a33b25ae86..edbf9c998848 100644 --- a/arch/x86/mm/mem_encrypt_boot.S +++ b/arch/x86/mm/mem_encrypt_boot.S @@ -16,7 +16,7 @@ =20 .text .code64 -SYM_FUNC_START(sme_encrypt_execute) +SYM_FUNC_START(__pi_sme_encrypt_execute) =20 /* * 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) =20 -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 aeefc749e237..92ce18886477 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -3575,7 +3575,8 @@ static int validate_branch(struct objtool_file *file,= struct symbol *func, if (func && insn_func(insn) && func !=3D 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; =20 if (file->ignore_unreachables) --=20 2.51.0.268.g9569e192d0-goog