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    Subject[PATCH 4.19 134/195] KVM: x86: Protect MSR-based index computations in fixed_msr_to_seg_unit() from Spectre-v1/L1TF attacks
    Date
    From: Marios Pomonis <pomonis@google.com>

    commit 25a5edea71b7c154b6a0b8cec14c711cafa31d26 upstream.

    This fixes a Spectre-v1/L1TF vulnerability in fixed_msr_to_seg_unit().
    This function contains index computations based on the
    (attacker-controlled) MSR number.

    Fixes: de9aef5e1ad6 ("KVM: MTRR: introduce fixed_mtrr_segment table")

    Signed-off-by: Nick Finco <nifi@google.com>
    Signed-off-by: Marios Pomonis <pomonis@google.com>
    Reviewed-by: Andrew Honig <ahonig@google.com>
    Cc: stable@vger.kernel.org
    Reviewed-by: Jim Mattson <jmattson@google.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kvm/mtrr.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    --- a/arch/x86/kvm/mtrr.c
    +++ b/arch/x86/kvm/mtrr.c
    @@ -194,11 +194,15 @@ static bool fixed_msr_to_seg_unit(u32 ms
    break;
    case MSR_MTRRfix16K_80000 ... MSR_MTRRfix16K_A0000:
    *seg = 1;
    - *unit = msr - MSR_MTRRfix16K_80000;
    + *unit = array_index_nospec(
    + msr - MSR_MTRRfix16K_80000,
    + MSR_MTRRfix16K_A0000 - MSR_MTRRfix16K_80000 + 1);
    break;
    case MSR_MTRRfix4K_C0000 ... MSR_MTRRfix4K_F8000:
    *seg = 2;
    - *unit = msr - MSR_MTRRfix4K_C0000;
    + *unit = array_index_nospec(
    + msr - MSR_MTRRfix4K_C0000,
    + MSR_MTRRfix4K_F8000 - MSR_MTRRfix4K_C0000 + 1);
    break;
    default:
    return false;

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