[PATCH 3.11 244/272] KVM: x86: fix emulation of "movzbl %bpl, %eax"

From: Luis Henriques
Date: Fri Dec 06 2013 - 08:13:35 EST


3.11.10.1 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

commit daf727225b8abfdfe424716abac3d15a3ac5626a upstream.

When I was looking at RHEL5.9's failure to start with
unrestricted_guest=0/emulate_invalid_guest_state=1, I got it working with a
slightly older tree than kvm.git. I now debugged the remaining failure,
which was introduced by commit 660696d1 (KVM: X86 emulator: fix
source operand decoding for 8bit mov[zs]x instructions, 2013-04-24)
introduced a similar mis-emulation to the one in commit 8acb4207 (KVM:
fix sil/dil/bpl/spl in the mod/rm fields, 2013-05-30). The incorrect
decoding occurs in 8-bit movzx/movsx instructions whose 8-bit operand
is sil/dil/bpl/spl.

Needless to say, "movzbl %bpl, %eax" does occur in RHEL5.9's decompression
prolog, just a handful of instructions before finally giving control to
the decompressed vmlinux and getting out of the invalid guest state.

Because OpMem8 bypasses decode_modrm, the same handling of the REX prefix
must be applied to OpMem8.

Reported-by: Michele Baldessari <michele@xxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
arch/x86/kvm/emulate.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 2bc1e81..7210ee3 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4028,7 +4028,10 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
case OpMem8:
ctxt->memop.bytes = 1;
if (ctxt->memop.type == OP_REG) {
- ctxt->memop.addr.reg = decode_register(ctxt, ctxt->modrm_rm, 1);
+ int highbyte_regs = ctxt->rex_prefix == 0;
+
+ ctxt->memop.addr.reg = decode_register(ctxt, ctxt->modrm_rm,
+ highbyte_regs);
fetch_register_operand(&ctxt->memop);
}
goto mem_common;
--
1.8.3.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/