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KVM: x86 emulator: preserve an operand's segment identity
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Currently the x86 emulator converts the segment register associated with
an operand into a segment base which is added into the operand address.
This loss of information results in us not doing segment limit checks properly.

Replace struct operand's addr.mem field by a segmented_address structure
which holds both the effetive address and segment.  This will allow us to
do the limit check at the point of access.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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Avi Kivity committed Jan 12, 2011
1 parent d53db5e commit 90de84f
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Showing 2 changed files with 59 additions and 52 deletions.
5 changes: 4 additions & 1 deletion arch/x86/include/asm/kvm_emulate.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -159,7 +159,10 @@ struct operand {
};
union {
unsigned long *reg;
unsigned long mem;
struct segmented_address {
ulong ea;
unsigned seg;
} mem;
} addr;
union {
unsigned long val;
Expand Down
106 changes: 55 additions & 51 deletions arch/x86/kvm/emulate.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -410,9 +410,9 @@ address_mask(struct decode_cache *c, unsigned long reg)
}

static inline unsigned long
register_address(struct decode_cache *c, unsigned long base, unsigned long reg)
register_address(struct decode_cache *c, unsigned long reg)
{
return base + address_mask(c, reg);
return address_mask(c, reg);
}

static inline void
Expand Down Expand Up @@ -444,26 +444,26 @@ static unsigned long seg_base(struct x86_emulate_ctxt *ctxt,
return ops->get_cached_segment_base(seg, ctxt->vcpu);
}

static unsigned long seg_override_base(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops,
struct decode_cache *c)
static unsigned seg_override(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops,
struct decode_cache *c)
{
if (!c->has_seg_override)
return 0;

return seg_base(ctxt, ops, c->seg_override);
return c->seg_override;
}

static unsigned long es_base(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops)
static ulong linear(struct x86_emulate_ctxt *ctxt,
struct segmented_address addr)
{
return seg_base(ctxt, ops, VCPU_SREG_ES);
}
struct decode_cache *c = &ctxt->decode;
ulong la;

static unsigned long ss_base(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops)
{
return seg_base(ctxt, ops, VCPU_SREG_SS);
la = seg_base(ctxt, ctxt->ops, addr.seg) + addr.ea;
if (c->ad_bytes != 8)
la &= (u32)-1;
return la;
}

static void emulate_exception(struct x86_emulate_ctxt *ctxt, int vec,
Expand Down Expand Up @@ -556,18 +556,20 @@ static void *decode_register(u8 modrm_reg, unsigned long *regs,

static int read_descriptor(struct x86_emulate_ctxt *ctxt,
struct x86_emulate_ops *ops,
ulong addr,
struct segmented_address addr,
u16 *size, unsigned long *address, int op_bytes)
{
int rc;

if (op_bytes == 2)
op_bytes = 3;
*address = 0;
rc = ops->read_std(addr, (unsigned long *)size, 2, ctxt->vcpu, NULL);
rc = ops->read_std(linear(ctxt, addr), (unsigned long *)size, 2,
ctxt->vcpu, NULL);
if (rc != X86EMUL_CONTINUE)
return rc;
rc = ops->read_std(addr + 2, address, op_bytes, ctxt->vcpu, NULL);
rc = ops->read_std(linear(ctxt, addr) + 2, address, op_bytes,
ctxt->vcpu, NULL);
return rc;
}

Expand Down Expand Up @@ -760,7 +762,7 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
break;
}
}
op->addr.mem = modrm_ea;
op->addr.mem.ea = modrm_ea;
done:
return rc;
}
Expand All @@ -775,13 +777,13 @@ static int decode_abs(struct x86_emulate_ctxt *ctxt,
op->type = OP_MEM;
switch (c->ad_bytes) {
case 2:
op->addr.mem = insn_fetch(u16, 2, c->eip);
op->addr.mem.ea = insn_fetch(u16, 2, c->eip);
break;
case 4:
op->addr.mem = insn_fetch(u32, 4, c->eip);
op->addr.mem.ea = insn_fetch(u32, 4, c->eip);
break;
case 8:
op->addr.mem = insn_fetch(u64, 8, c->eip);
op->addr.mem.ea = insn_fetch(u64, 8, c->eip);
break;
}
done:
Expand All @@ -800,7 +802,7 @@ static void fetch_bit_operand(struct decode_cache *c)
else if (c->src.bytes == 4)
sv = (s32)c->src.val & (s32)mask;

c->dst.addr.mem += (sv >> 3);
c->dst.addr.mem.ea += (sv >> 3);
}

/* only subword offset */
Expand Down Expand Up @@ -1093,15 +1095,15 @@ static inline int writeback(struct x86_emulate_ctxt *ctxt,
case OP_MEM:
if (c->lock_prefix)
rc = ops->cmpxchg_emulated(
c->dst.addr.mem,
linear(ctxt, c->dst.addr.mem),
&c->dst.orig_val,
&c->dst.val,
c->dst.bytes,
&err,
ctxt->vcpu);
else
rc = ops->write_emulated(
c->dst.addr.mem,
linear(ctxt, c->dst.addr.mem),
&c->dst.val,
c->dst.bytes,
&err,
Expand Down Expand Up @@ -1129,8 +1131,8 @@ static inline void emulate_push(struct x86_emulate_ctxt *ctxt,
c->dst.bytes = c->op_bytes;
c->dst.val = c->src.val;
register_address_increment(c, &c->regs[VCPU_REGS_RSP], -c->op_bytes);
c->dst.addr.mem = register_address(c, ss_base(ctxt, ops),
c->regs[VCPU_REGS_RSP]);
c->dst.addr.mem.ea = register_address(c, c->regs[VCPU_REGS_RSP]);
c->dst.addr.mem.seg = VCPU_SREG_SS;
}

static int emulate_pop(struct x86_emulate_ctxt *ctxt,
Expand All @@ -1139,10 +1141,11 @@ static int emulate_pop(struct x86_emulate_ctxt *ctxt,
{
struct decode_cache *c = &ctxt->decode;
int rc;
struct segmented_address addr;

rc = read_emulated(ctxt, ops, register_address(c, ss_base(ctxt, ops),
c->regs[VCPU_REGS_RSP]),
dest, len);
addr.ea = register_address(c, c->regs[VCPU_REGS_RSP]);
addr.seg = VCPU_SREG_SS;
rc = read_emulated(ctxt, ops, linear(ctxt, addr), dest, len);
if (rc != X86EMUL_CONTINUE)
return rc;

Expand Down Expand Up @@ -2223,14 +2226,15 @@ int emulator_task_switch(struct x86_emulate_ctxt *ctxt,
return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
}

static void string_addr_inc(struct x86_emulate_ctxt *ctxt, unsigned long base,
static void string_addr_inc(struct x86_emulate_ctxt *ctxt, unsigned seg,
int reg, struct operand *op)
{
struct decode_cache *c = &ctxt->decode;
int df = (ctxt->eflags & EFLG_DF) ? -1 : 1;

register_address_increment(c, &c->regs[reg], df * op->bytes);
op->addr.mem = register_address(c, base, c->regs[reg]);
op->addr.mem.ea = register_address(c, c->regs[reg]);
op->addr.mem.seg = seg;
}

static int em_push(struct x86_emulate_ctxt *ctxt)
Expand Down Expand Up @@ -2639,7 +2643,7 @@ static int decode_imm(struct x86_emulate_ctxt *ctxt, struct operand *op,

op->type = OP_IMM;
op->bytes = size;
op->addr.mem = c->eip;
op->addr.mem.ea = c->eip;
/* NB. Immediates are sign-extended as necessary. */
switch (op->bytes) {
case 1:
Expand Down Expand Up @@ -2821,14 +2825,13 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
if (!c->has_seg_override)
set_seg_override(c, VCPU_SREG_DS);

if (memop.type == OP_MEM && !(!c->twobyte && c->b == 0x8d))
memop.addr.mem += seg_override_base(ctxt, ops, c);
memop.addr.mem.seg = seg_override(ctxt, ops, c);

if (memop.type == OP_MEM && c->ad_bytes != 8)
memop.addr.mem = (u32)memop.addr.mem;
memop.addr.mem.ea = (u32)memop.addr.mem.ea;

if (memop.type == OP_MEM && c->rip_relative)
memop.addr.mem += c->eip;
memop.addr.mem.ea += c->eip;

/*
* Decode and fetch the source operand: register, memory
Expand Down Expand Up @@ -2880,14 +2883,14 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
case SrcSI:
c->src.type = OP_MEM;
c->src.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
c->src.addr.mem =
register_address(c, seg_override_base(ctxt, ops, c),
c->regs[VCPU_REGS_RSI]);
c->src.addr.mem.ea =
register_address(c, c->regs[VCPU_REGS_RSI]);
c->src.addr.mem.seg = seg_override(ctxt, ops, c),
c->src.val = 0;
break;
case SrcImmFAddr:
c->src.type = OP_IMM;
c->src.addr.mem = c->eip;
c->src.addr.mem.ea = c->eip;
c->src.bytes = c->op_bytes + 2;
insn_fetch_arr(c->src.valptr, c->src.bytes, c->eip);
break;
Expand Down Expand Up @@ -2934,7 +2937,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
break;
case DstImmUByte:
c->dst.type = OP_IMM;
c->dst.addr.mem = c->eip;
c->dst.addr.mem.ea = c->eip;
c->dst.bytes = 1;
c->dst.val = insn_fetch(u8, 1, c->eip);
break;
Expand All @@ -2959,9 +2962,9 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
case DstDI:
c->dst.type = OP_MEM;
c->dst.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
c->dst.addr.mem =
register_address(c, es_base(ctxt, ops),
c->regs[VCPU_REGS_RDI]);
c->dst.addr.mem.ea =
register_address(c, c->regs[VCPU_REGS_RDI]);
c->dst.addr.mem.seg = VCPU_SREG_ES;
c->dst.val = 0;
break;
case ImplicitOps:
Expand Down Expand Up @@ -3040,15 +3043,15 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
}

if ((c->src.type == OP_MEM) && !(c->d & NoAccess)) {
rc = read_emulated(ctxt, ops, c->src.addr.mem,
rc = read_emulated(ctxt, ops, linear(ctxt, c->src.addr.mem),
c->src.valptr, c->src.bytes);
if (rc != X86EMUL_CONTINUE)
goto done;
c->src.orig_val64 = c->src.val64;
}

if (c->src2.type == OP_MEM) {
rc = read_emulated(ctxt, ops, c->src2.addr.mem,
rc = read_emulated(ctxt, ops, linear(ctxt, c->src2.addr.mem),
&c->src2.val, c->src2.bytes);
if (rc != X86EMUL_CONTINUE)
goto done;
Expand All @@ -3060,7 +3063,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)

if ((c->dst.type == OP_MEM) && !(c->d & Mov)) {
/* optimisation - avoid slow emulated read if Mov */
rc = read_emulated(ctxt, ops, c->dst.addr.mem,
rc = read_emulated(ctxt, ops, linear(ctxt, c->dst.addr.mem),
&c->dst.val, c->dst.bytes);
if (rc != X86EMUL_CONTINUE)
goto done;
Expand Down Expand Up @@ -3211,7 +3214,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
c->dst.val = ops->get_segment_selector(c->modrm_reg, ctxt->vcpu);
break;
case 0x8d: /* lea r16/r32, m */
c->dst.val = c->src.addr.mem;
c->dst.val = c->src.addr.mem.ea;
break;
case 0x8e: { /* mov seg, r/m16 */
uint16_t sel;
Expand Down Expand Up @@ -3438,11 +3441,11 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
c->dst.type = saved_dst_type;

if ((c->d & SrcMask) == SrcSI)
string_addr_inc(ctxt, seg_override_base(ctxt, ops, c),
string_addr_inc(ctxt, seg_override(ctxt, ops, c),
VCPU_REGS_RSI, &c->src);

if ((c->d & DstMask) == DstDI)
string_addr_inc(ctxt, es_base(ctxt, ops), VCPU_REGS_RDI,
string_addr_inc(ctxt, VCPU_SREG_ES, VCPU_REGS_RDI,
&c->dst);

if (c->rep_prefix && (c->d & String)) {
Expand Down Expand Up @@ -3535,7 +3538,8 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
emulate_ud(ctxt);
goto done;
case 7: /* invlpg*/
emulate_invlpg(ctxt->vcpu, c->src.addr.mem);
emulate_invlpg(ctxt->vcpu,
linear(ctxt, c->src.addr.mem));
/* Disable writeback. */
c->dst.type = OP_NONE;
break;
Expand Down

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