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KVM: x86: Protect x86_decode_insn from Spectre-v1/L1TF attacks 

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: 045a282ca4 ("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>
This commit is contained in:
Marios Pomonis 2019-12-11 12:47:41 -08:00 committed by Paolo Bonzini
parent a47970ed74
commit 3c9053a2ca
1 changed files with 8 additions and 3 deletions
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11
arch/x86/kvm/emulate.c
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@ -5288,10 +5288,15 @@ 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)