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Date: Fri, 18 Feb 2022 17:49:17 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
ndesaulniers@...gle.com, keescook@...omium.org,
samitolvanen@...gle.com, mark.rutland@....com,
alyssa.milburn@...el.com
Subject: [PATCH 15/29] x86: Disable IBT around firmware
Assume firmware isn't IBT clean and disable it across calls.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/efi.h | 9 +++++++--
arch/x86/include/asm/ibt.h | 10 ++++++++++
arch/x86/kernel/apm_32.c | 7 +++++++
arch/x86/kernel/cpu/common.c | 28 ++++++++++++++++++++++++++++
4 files changed, 52 insertions(+), 2 deletions(-)
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -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 *f
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() \
({ \
--- a/arch/x86/include/asm/ibt.h
+++ b/arch/x86/include/asm/ibt.h
@@ -6,6 +6,8 @@
#ifndef __ASSEMBLY__
+#include <linux/types.h>
+
#ifdef CONFIG_X86_64
#define ASM_ENDBR "endbr64\n\t"
#else
@@ -25,6 +27,9 @@ static inline bool is_endbr(const void *
return val == ~0xfa1e0ff3;
}
+extern u64 ibt_save(void);
+extern void ibt_restore(u64 save);
+
#else /* __ASSEMBLY__ */
#ifdef CONFIG_X86_64
@@ -39,10 +44,15 @@ static inline bool is_endbr(const void *
#ifndef __ASSEMBLY__
+#include <linux/types.h>
+
#define ASM_ENDBR
#define __noendbr
+static inline u64 ibt_save(void) { return 0; }
+static inline void ibt_restore(u64 save) { }
+
#else /* __ASSEMBLY__ */
#define ENDBR
--- a/arch/x86/kernel/apm_32.c
+++ b/arch/x86/kernel/apm_32.c
@@ -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
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
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;
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -592,6 +592,34 @@ static __init int setup_disable_pku(char
__setup("nopku", setup_disable_pku);
#endif /* CONFIG_X86_64 */
+#ifdef CONFIG_X86_IBT
+
+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;
+}
+
+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;
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