From daf727225b8abfdfe424716abac3d15a3ac5626a Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 31 Oct 2013 23:05:24 +0100 Subject: [PATCH] KVM: x86: fix emulation of "movzbl %bpl, %eax" 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 Cc: stable@vger.kernel.org Cc: Gleb Natapov Signed-off-by: Paolo Bonzini Signed-off-by: Gleb Natapov --- 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 16c037e7db7d..282d28cb9931 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4117,7 +4117,10 @@ 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;