Commit fe379fa4 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

x86/ibt: Disable IBT around firmware 



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

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.759989383@infradead.org
parent 99c95c5d

arch/x86/include/asm/efi.h

+7 −2
Original line number Diff line number Diff line
@@ -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()					\

({									\

arch/x86/include/asm/ibt.h

+6 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/apm_32.c

+7 −0
Original line number Diff line number Diff line
@@ -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;

arch/x86/kernel/cpu/common.c

+28 −0
Original line number Diff line number Diff line
@@ -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;