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authorRusty Russell <rusty@rustcorp.com.au>2011-07-22 14:39:51 +0930
committerRusty Russell <rusty@rustcorp.com.au>2011-07-22 14:39:51 +0930
commit996ba96a97f7406052486682846d68935a60e986 (patch)
treef02f603742129314a497d3406b02a7f929893d9c
parent8d431f41603acff8a20cf5df99bc8958c91879c1 (diff)
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lguest: Fix in/out emulation
We were blatting too much of the register. Linux didn't care, but in theory it might. Reported-by: Jonas Maebe <jonas.maebe@elis.ugent.be> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--drivers/lguest/x86/core.c20
1 files changed, 11 insertions, 9 deletions
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 3b9b810cbf2..65af42f2d59 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -269,7 +269,7 @@ void lguest_arch_run_guest(struct lg_cpu *cpu)
static int emulate_insn(struct lg_cpu *cpu)
{
u8 insn;
- unsigned int insnlen = 0, in = 0, shift = 0;
+ unsigned int insnlen = 0, in = 0, small_operand = 0;
/*
* The eip contains the *virtual* address of the Guest's instruction:
* walk the Guest's page tables to find the "physical" address.
@@ -300,11 +300,10 @@ static int emulate_insn(struct lg_cpu *cpu)
}
/*
- * 0x66 is an "operand prefix". It means it's using the upper 16 bits
- * of the eax register.
+ * 0x66 is an "operand prefix". It means a 16, not 32 bit in/out.
*/
if (insn == 0x66) {
- shift = 16;
+ small_operand = 1;
/* The instruction is 1 byte so far, read the next byte. */
insnlen = 1;
insn = lgread(cpu, physaddr + insnlen, u8);
@@ -340,11 +339,14 @@ static int emulate_insn(struct lg_cpu *cpu)
* traditionally means "there's nothing there".
*/
if (in) {
- /* Lower bit tells is whether it's a 16 or 32 bit access */
- if (insn & 0x1)
- cpu->regs->eax = 0xFFFFFFFF;
- else
- cpu->regs->eax |= (0xFFFF << shift);
+ /* Lower bit tells means it's a 32/16 bit access */
+ if (insn & 0x1) {
+ if (small_operand)
+ cpu->regs->eax |= 0xFFFF;
+ else
+ cpu->regs->eax = 0xFFFFFFFF;
+ } else
+ cpu->regs->eax |= 0xFF;
}
/* Finally, we've "done" the instruction, so move past it. */
cpu->regs->eip += insnlen;