The sub-register used to access the stack (sp, esp, or rsp) is not
determined by the address size attribute like other memory references,
but by the stack segment's B bit (if not in x86_64 mode).
Fix by using the existing stack_mask() to figure out the correct mask.
This long-existing bug was exposed by a combination of a27685c33acccce
(emulate invalid guest state by default), which causes many more
instructions to be emulated, and a seabios change (possibly a bug) which
causes the high 16 bits of esp to become polluted across calls to real
mode software interrupts.
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
---
arch/x86/kvm/emulate.c | 30 +++++++++++++++++++++---------
1 file changed, 21 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 97d9a99..a3b57a2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -475,13 +475,26 @@ static int stack_size(struct x86_emulate_ctxt *ctxt)
return address_mask(ctxt, reg);
}
+static void masked_increment(ulong *reg, ulong mask, int inc)
+{
+ assign_masked(reg, *reg + inc, mask);
+}
+
static inline void
register_address_increment(struct x86_emulate_ctxt *ctxt, unsigned long *reg, int inc)
{
+ ulong mask;
+
if (ctxt->ad_bytes == sizeof(unsigned long))
- *reg += inc;
+ mask = ~0UL;
else
- *reg = (*reg & ~ad_mask(ctxt)) | ((*reg + inc) & ad_mask(ctxt));
+ mask = ad_mask(ctxt);
+ masked_increment(reg, mask, inc);
+}
+
+static void rsp_increment(struct x86_emulate_ctxt *ctxt, int inc)
+{
+ masked_increment(&ctxt->regs[VCPU_REGS_RSP], stack_mask(ctxt), inc);
}
static inline void jmp_rel(struct x86_emulate_ctxt *ctxt, int rel)
@@ -1522,8 +1535,8 @@ static int push(struct x86_emulate_ctxt *ctxt, void *data, int bytes)
{
struct segmented_address addr;
- register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RSP], -bytes);
- addr.ea = register_address(ctxt, ctxt->regs[VCPU_REGS_RSP]);
+ rsp_increment(ctxt, -bytes);
+ addr.ea = ctxt->regs[VCPU_REGS_RSP] & stack_mask(ctxt);
addr.seg = VCPU_SREG_SS;
return segmented_write(ctxt, addr, data, bytes);
@@ -1542,13 +1555,13 @@ static int emulate_pop(struct x86_emulate_ctxt *ctxt,
int rc;
struct segmented_address addr;
- addr.ea = register_address(ctxt, ctxt->regs[VCPU_REGS_RSP]);
+ addr.ea = ctxt->regs[VCPU_REGS_RSP] & stack_mask(ctxt);
addr.seg = VCPU_SREG_SS;
rc = segmented_read(ctxt, addr, dest, len);
if (rc != X86EMUL_CONTINUE)
return rc;
- register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RSP], len);
+ rsp_increment(ctxt, len);
return rc;
}
@@ -1688,8 +1701,7 @@ static int em_popa(struct x86_emulate_ctxt *ctxt)
while (reg >= VCPU_REGS_RAX) {
if (reg == VCPU_REGS_RSP) {
- register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RSP],
- ctxt->op_bytes);
+ rsp_increment(ctxt, ctxt->op_bytes);
--reg;
}
@@ -2825,7 +2837,7 @@ static int em_ret_near_imm(struct x86_emulate_ctxt *ctxt)
rc = emulate_pop(ctxt, &ctxt->dst.val, ctxt->op_bytes);
if (rc != X86EMUL_CONTINUE)
return rc;
- register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RSP], ctxt->src.val);
+ rsp_increment(ctxt, ctxt->src.val);
return X86EMUL_CONTINUE;
}
--
1.7.11.3
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