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Subject[PATCH v2 01/13] KVM: x86: Protect x86_decode_insn from Spectre-v1/L1TF attacks
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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: commit 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
---
arch/x86/kvm/emulate.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 952d1a4f4d7e..fcf7cdb21d60 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5303,10 +5303,15 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
}
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)
--
2.24.0.525.g8f36a354ae-goog
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