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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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