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    Subject[PATCH 4.14 087/173] KVM: x86: Protect x86_decode_insn from Spectre-v1/L1TF attacks
    Date
    From: Marios Pomonis <pomonis@google.com>

    commit 3c9053a2cae7ba2ba73766a34cea41baa70f57f7 upstream.

    This fixes a Spectre-v1/L1TF vulnerability in x86_decode_insn().
    kvm_emulate_instruction() (an ancestor of x86_decode_insn()) is an exported
    symbol, so KVM should treat it conservatively from a security perspective.

    Fixes: 045a282ca415 ("KVM: emulator: implement fninit, fnstsw, fnstcw")

    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/emulate.c | 11 ++++++++---
    1 file changed, 8 insertions(+), 3 deletions(-)

    --- a/arch/x86/kvm/emulate.c
    +++ b/arch/x86/kvm/emulate.c
    @@ -5199,10 +5199,15 @@ done_prefixes:
    }
    break;
    case Escape:
    - if (ctxt->modrm > 0xbf)
    - opcode = opcode.u.esc->high[ctxt->modrm - 0xc0];
    - else
    + if (ctxt->modrm > 0xbf) {
    + size_t size = ARRAY_SIZE(opcode.u.esc->high);
    + u32 index = array_index_nospec(
    + ctxt->modrm - 0xc0, size);
    +
    + opcode = opcode.u.esc->high[index];
    + } else {
    opcode = opcode.u.esc->op[(ctxt->modrm >> 3) & 7];
    + }
    break;
    case InstrDual:
    if ((ctxt->modrm >> 6) == 3)

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