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Subject[PATCH v4 25/45] x86/ibt,kexec: Disable CET on kexec

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/cpu.h | 3 +++
arch/x86/kernel/cpu/common.c | 6 ++++++
arch/x86/kernel/machine_kexec_64.c | 4 +++-
arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++
4 files changed, 20 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -73,4 +73,7 @@ void init_ia32_feat_ctl(struct cpuinfo_x
#else
static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
#endif
+
+extern __noendbr void cet_disable(void);
+
#endif /* _ASM_X86_CPU_H */
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -612,6 +612,12 @@ static __always_inline void setup_cet(st
}
}

+__noendbr void cet_disable(void)
+{
+ if (cpu_feature_enabled(X86_FEATURE_IBT))
+ wrmsrl(MSR_IA32_S_CET, 0);
+}
+
/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -27,6 +27,7 @@
#include <asm/kexec-bzimage64.h>
#include <asm/setup.h>
#include <asm/set_memory.h>
+#include <asm/cpu.h>

#ifdef CONFIG_ACPI
/*
@@ -310,6 +311,7 @@ void machine_kexec(struct kimage *image)
/* Interrupts aren't acceptable while we reboot */
local_irq_disable();
hw_breakpoint_disable();
+ cet_disable();

if (image->preserve_context) {
#ifdef CONFIG_X86_IO_APIC
@@ -325,7 +327,7 @@ void machine_kexec(struct kimage *image)
}

control_page = page_address(image->control_code_page) + PAGE_SIZE;
- memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
+ __memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);

page_list[PA_CONTROL_PAGE] = virt_to_phys(control_page);
page_list[VA_CONTROL_PAGE] = (unsigned long)control_page;
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -115,6 +115,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_ma
pushq %rdx

/*
+ * Clear X86_CR4_CET (if it was set) such that we can clear CR0_WP
+ * below.
+ */
+ movq %cr4, %rax
+ andq $~(X86_CR4_CET), %rax
+ movq %rax, %cr4
+
+ /*
* Set cr0 to a known state:
* - Paging enabled
* - Alignment check disabled

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