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x86/ibt: Disable IBT around firmware

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Assume firmware isn't IBT clean and disable it across calls.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.759989383@infradead.org
This commit is contained in:
Peter Zijlstra 2022-03-08 16:30:38 +01:00
parent 99c95c5d4f
commit fe379fa4d1
4 changed files with 48 additions and 2 deletions
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9
arch/x86/include/asm/efi.h
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@ -7,6 +7,7 @@
#include <asm/tlb.h>
#include <asm/nospec-branch.h>
#include <asm/mmu_context.h>
#include <asm/ibt.h>
#include <linux/build_bug.h>
#include <linux/kernel.h>
#include <linux/pgtable.h>
@ -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() \
({ \

6
arch/x86/include/asm/ibt.h
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@ -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

7
arch/x86/kernel/apm_32.c
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@ -232,6 +232,7 @@
#include <asm/paravirt.h>
#include <asm/reboot.h>
#include <asm/nospec-branch.h>
#include <asm/ibt.h>
#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;

28
arch/x86/kernel/cpu/common.c
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@ -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;