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

@@ -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 */

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

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;

arch/x86/kernel/relocate_kernel_64.S

@@ -114,6 +114,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	/* store the start address on the stack */
 	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