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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>
This commit is contained in:
Rusty Russell 2011-07-22 14:39:51 +09:30
parent 8d431f4160
commit 996ba96a97
1 changed files with 11 additions and 9 deletions
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20
drivers/lguest/x86/core.c
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@ -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;