KVM: emulator: emulate SALC

This is an almost-undocumented instruction available in 32-bit mode.
I say "almost" undocumented because AMD documents it in their opcode
maps just to say that it is unavailable in 64-bit mode (sections
"A.2.1 One-Byte Opcodes" and "B.3 Invalid and Reassigned Instructions
in 64-Bit Mode").

It is roughly equivalent to "sbb %al, %al" except it does not
set the flags.  Use fastop to emulate it, but do not use the opcode
directly because it would fail if the host is 64-bit!

Reported-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: stable@vger.kernel.org # 3.9
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index a06a550c2db8..8db0010ed150 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -535,6 +535,9 @@ FOP_SETCC(setle)
 FOP_SETCC(setnle)
 FOP_END;
 
+FOP_START(salc) "pushf; sbb %al, %al; popf \n\t" FOP_RET
+FOP_END;
+
 #define __emulate_1op_rax_rdx(ctxt, _op, _suffix, _ex)                  \
         do {                                                            \
                 unsigned long _tmp;                                     \
@@ -3961,7 +3964,8 @@ static const struct opcode opcode_table[256] = {
         G(Src2One | ByteOp, group2), G(Src2One, group2),
         G(Src2CL | ByteOp, group2), G(Src2CL, group2),
         I(DstAcc | SrcImmUByte | No64, em_aam),
-        I(DstAcc | SrcImmUByte | No64, em_aad), N,
+        I(DstAcc | SrcImmUByte | No64, em_aad),
+        F(DstAcc | ByteOp | No64, em_salc),
         I(DstAcc | SrcXLat | ByteOp, em_mov),
         /* 0xD8 - 0xDF */
         N, E(0, &escape_d9), N, E(0, &escape_db), N, E(0, &escape_dd), N, N,