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Subject[tip: x86/core] x86/ibt,kexec: Disable CET on kexec
The following commit has been merged into the x86/core branch of tip:

Commit-ID: f9a08abb06d0abe51295479118f1f8e4a4325798
Gitweb: https://git.kernel.org/tip/f9a08abb06d0abe51295479118f1f8e4a4325798
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 08 Mar 2022 16:30:36 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Mar 2022 23:53:33 +01:00

x86/ibt,kexec: Disable CET on kexec

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.641454603@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(-)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index a60025f..86e5e4e 100644
--- 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_x86 *c);
#else
static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
#endif
+
+extern __noendbr void cet_disable(void);
+
#endif /* _ASM_X86_CPU_H */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index db1f149..709acab 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -535,6 +535,12 @@ static __always_inline void setup_cet(struct cpuinfo_x86 *c)
}
}

+__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
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index f5da4a1..566bb8e 100644
--- 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;
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 399f075..5b65f6e 100644
--- 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_mapped)
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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