From 5aca3722362689a679419dc9b3e426921c70ef16 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Sun, 2 Nov 2014 11:54:50 +0200 Subject: [PATCH] KVM: x86: Wrong flags on CMPS and SCAS emulation CMPS and SCAS instructions are evaluated in the wrong order. For reference (of CMPS), see http://www.fermimn.gov.it/linux/quarta/x86/cmps.htm : "Note that the direction of subtraction for CMPS is [SI] - [DI] or [ESI] - [EDI]. The left operand (SI or ESI) is the source and the right operand (DI or EDI) is the destination. This is the reverse of the usual Intel convention in which the left operand is the destination and the right operand is the source." Introducing em_cmp_r for this matter that performs comparison in reverse order using fastop infrastructure to avoid a wrapper function. Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index e475cdff15e1..7aba1db168c9 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -380,6 +380,15 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *)); ON64(FOP2E(op##q, rax, cl)) \ FOP_END +/* 2 operand, src and dest are reversed */ +#define FASTOP2R(op, name) \ + FOP_START(name) \ + FOP2E(op##b, dl, al) \ + FOP2E(op##w, dx, ax) \ + FOP2E(op##l, edx, eax) \ + ON64(FOP2E(op##q, rdx, rax)) \ + FOP_END + #define FOP3E(op, dst, src, src2) \ FOP_ALIGN #op " %" #src2 ", %" #src ", %" #dst " \n\t" FOP_RET @@ -913,6 +922,8 @@ FASTOP2W(btc); FASTOP2(xadd); +FASTOP2R(cmp, cmp_r); + static u8 test_cc(unsigned int condition, unsigned long flags) { u8 rc; @@ -3993,12 +4004,12 @@ static const struct opcode opcode_table[256] = { I2bv(DstAcc | SrcMem | Mov | MemAbs, em_mov), I2bv(DstMem | SrcAcc | Mov | MemAbs | PageTable, em_mov), I2bv(SrcSI | DstDI | Mov | String, em_mov), - F2bv(SrcSI | DstDI | String | NoWrite, em_cmp), + F2bv(SrcSI | DstDI | String | NoWrite, em_cmp_r), /* 0xA8 - 0xAF */ F2bv(DstAcc | SrcImm | NoWrite, em_test), I2bv(SrcAcc | DstDI | Mov | String, em_mov), I2bv(SrcSI | DstAcc | Mov | String, em_mov), - F2bv(SrcAcc | DstDI | String | NoWrite, em_cmp), + F2bv(SrcAcc | DstDI | String | NoWrite, em_cmp_r), /* 0xB0 - 0xB7 */ X8(I(ByteOp | DstReg | SrcImm | Mov, em_mov)), /* 0xB8 - 0xBF */ -- 2.20.1