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    Subject[PATCH 5.5 105/189] x86/pkeys: Manually set X86_FEATURE_OSPKE to preserve existing changes
    Date
    From: Sean Christopherson <sean.j.christopherson@intel.com>

    commit 735a6dd02222d8d070c7bb748f25895239ca8c92 upstream.

    Explicitly set X86_FEATURE_OSPKE via set_cpu_cap() instead of calling
    get_cpu_cap() to pull the feature bit from CPUID after enabling CR4.PKE.
    Invoking get_cpu_cap() effectively wipes out any {set,clear}_cpu_cap()
    changes that were made between this_cpu->c_init() and setup_pku(), as
    all non-synthetic feature words are reinitialized from the CPU's CPUID
    values.

    Blasting away capability updates manifests most visibility when running
    on a VMX capable CPU, but with VMX disabled by BIOS. To indicate that
    VMX is disabled, init_ia32_feat_ctl() clears X86_FEATURE_VMX, using
    clear_cpu_cap() instead of setup_clear_cpu_cap() so that KVM can report
    which CPU is misconfigured (KVM needs to probe every CPU anyways).
    Restoring X86_FEATURE_VMX from CPUID causes KVM to think VMX is enabled,
    ultimately leading to an unexpected #GP when KVM attempts to do VMXON.

    Arguably, init_ia32_feat_ctl() should use setup_clear_cpu_cap() and let
    KVM figure out a different way to report the misconfigured CPU, but VMX
    is not the only feature bit that is affected, i.e. there is precedent
    that tweaking feature bits via {set,clear}_cpu_cap() after ->c_init()
    is expected to work. Most notably, x86_init_rdrand()'s clearing of
    X86_FEATURE_RDRAND when RDRAND malfunctions is also overwritten.

    Fixes: 0697694564c8 ("x86/mm/pkeys: Actually enable Memory Protection Keys in the CPU")
    Reported-by: Jacob Keller <jacob.e.keller@intel.com>
    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
    Tested-by: Jacob Keller <jacob.e.keller@intel.com>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20200226231615.13664-1-sean.j.christopherson@intel.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kernel/cpu/common.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/x86/kernel/cpu/common.c
    +++ b/arch/x86/kernel/cpu/common.c
    @@ -462,7 +462,7 @@ static __always_inline void setup_pku(st
    * cpuid bit to be set. We need to ensure that we
    * update that bit in this CPU's "cpu_info".
    */
    - get_cpu_cap(c);
    + set_cpu_cap(c, X86_FEATURE_OSPKE);
    }

    #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS

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