From fe379fa4d199abc52d5b4a256e52cf94eff685cf Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 8 Mar 2022 16:30:38 +0100 Subject: [PATCH] x86/ibt: Disable IBT around firmware Assume firmware isn't IBT clean and disable it across calls. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Kees Cook Acked-by: Josh Poimboeuf Link: https://lore.kernel.org/r/20220308154318.759989383@infradead.org --- arch/x86/include/asm/efi.h | 9 +++++++-- arch/x86/include/asm/ibt.h | 6 ++++++ arch/x86/kernel/apm_32.c | 7 +++++++ arch/x86/kernel/cpu/common.c | 28 ++++++++++++++++++++++++++++ 4 files changed, 48 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h index 03cb12775043..98938a68251c 100644 --- a/arch/x86/include/asm/efi.h +++ b/arch/x86/include/asm/efi.h @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -120,8 +121,12 @@ extern asmlinkage u64 __efi_call(void *fp, ...); efi_enter_mm(); \ }) -#define arch_efi_call_virt(p, f, args...) \ - efi_call((void *)p->f, args) \ +#define arch_efi_call_virt(p, f, args...) ({ \ + u64 ret, ibt = ibt_save(); \ + ret = efi_call((void *)p->f, args); \ + ibt_restore(ibt); \ + ret; \ +}) #define arch_efi_call_virt_teardown() \ ({ \ diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h index fcaf6a41d373..52fb05d66489 100644 --- a/arch/x86/include/asm/ibt.h +++ b/arch/x86/include/asm/ibt.h @@ -52,6 +52,9 @@ static inline bool is_endbr(u32 val) return val == gen_endbr(); } +extern __noendbr u64 ibt_save(void); +extern __noendbr void ibt_restore(u64 save); + #else /* __ASSEMBLY__ */ #ifdef CONFIG_X86_64 @@ -74,6 +77,9 @@ static inline bool is_endbr(u32 val) static inline bool is_endbr(u32 val) { return false; } +static inline u64 ibt_save(void) { return 0; } +static inline void ibt_restore(u64 save) { } + #else /* __ASSEMBLY__ */ #define ENDBR diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c index 241dda687eb9..60e330cdbd17 100644 --- a/arch/x86/kernel/apm_32.c +++ b/arch/x86/kernel/apm_32.c @@ -232,6 +232,7 @@ #include #include #include +#include #if defined(CONFIG_APM_DISPLAY_BLANK) && defined(CONFIG_VT) extern int (*console_blank_hook)(int); @@ -598,6 +599,7 @@ static long __apm_bios_call(void *_call) struct desc_struct save_desc_40; struct desc_struct *gdt; struct apm_bios_call *call = _call; + u64 ibt; cpu = get_cpu(); BUG_ON(cpu != 0); @@ -607,11 +609,13 @@ static long __apm_bios_call(void *_call) apm_irq_save(flags); firmware_restrict_branch_speculation_start(); + ibt = ibt_save(); APM_DO_SAVE_SEGS; apm_bios_call_asm(call->func, call->ebx, call->ecx, &call->eax, &call->ebx, &call->ecx, &call->edx, &call->esi); APM_DO_RESTORE_SEGS; + ibt_restore(ibt); firmware_restrict_branch_speculation_end(); apm_irq_restore(flags); gdt[0x40 / 8] = save_desc_40; @@ -676,6 +680,7 @@ static long __apm_bios_call_simple(void *_call) struct desc_struct save_desc_40; struct desc_struct *gdt; struct apm_bios_call *call = _call; + u64 ibt; cpu = get_cpu(); BUG_ON(cpu != 0); @@ -685,10 +690,12 @@ static long __apm_bios_call_simple(void *_call) apm_irq_save(flags); firmware_restrict_branch_speculation_start(); + ibt = ibt_save(); APM_DO_SAVE_SEGS; error = apm_bios_call_simple_asm(call->func, call->ebx, call->ecx, &call->eax); APM_DO_RESTORE_SEGS; + ibt_restore(ibt); firmware_restrict_branch_speculation_end(); apm_irq_restore(flags); gdt[0x40 / 8] = save_desc_40; diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 709acab25f3c..03bd73f16d74 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -517,6 +517,34 @@ static __init int setup_disable_pku(char *arg) __setup("nopku", setup_disable_pku); #endif /* CONFIG_X86_64 */ +#ifdef CONFIG_X86_KERNEL_IBT + +__noendbr u64 ibt_save(void) +{ + u64 msr = 0; + + if (cpu_feature_enabled(X86_FEATURE_IBT)) { + rdmsrl(MSR_IA32_S_CET, msr); + wrmsrl(MSR_IA32_S_CET, msr & ~CET_ENDBR_EN); + } + + return msr; +} + +__noendbr void ibt_restore(u64 save) +{ + u64 msr; + + if (cpu_feature_enabled(X86_FEATURE_IBT)) { + rdmsrl(MSR_IA32_S_CET, msr); + msr &= ~CET_ENDBR_EN; + msr |= (save & CET_ENDBR_EN); + wrmsrl(MSR_IA32_S_CET, msr); + } +} + +#endif + static __always_inline void setup_cet(struct cpuinfo_x86 *c) { u64 msr = CET_ENDBR_EN; -- 2.20.1