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lguest: Guest int3 fix

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Ron Minnich noticed that guest userspace gets a GPF when it tries to int3:
we need to copy the privilege level from the guest-supplied IDT to the real
IDT.  int3 is the only common case where guest userspace expects to invoke
an interrupt, so that's the symptom of failing to do this.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2008-07-29 09:58:31 -05:00
parent 5d006d8d09
commit 0c12091d82
1 changed files with 17 additions and 7 deletions
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24
drivers/lguest/interrupts_and_traps.c
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@ -406,7 +406,8 @@ void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int num, u32 lo, u32 hi)
* deliver_trap() to bounce it back into the Guest. */ * deliver_trap() to bounce it back into the Guest. */
static void default_idt_entry(struct desc_struct *idt, static void default_idt_entry(struct desc_struct *idt,
int trap, int trap,
const unsigned long handler) const unsigned long handler,
const struct desc_struct *base)
{ {
/* A present interrupt gate. */ /* A present interrupt gate. */
u32 flags = 0x8e00; u32 flags = 0x8e00;
@ -415,6 +416,10 @@ static void default_idt_entry(struct desc_struct *idt,
* the Guest to use the "int" instruction to trigger it. */ * the Guest to use the "int" instruction to trigger it. */
if (trap == LGUEST_TRAP_ENTRY) if (trap == LGUEST_TRAP_ENTRY)
flags |= (GUEST_PL << 13); flags |= (GUEST_PL << 13);
else if (base)
/* Copy priv. level from what Guest asked for. This allows
* debug (int 3) traps from Guest userspace, for example. */
flags |= (base->b & 0x6000);
/* Now pack it into the IDT entry in its weird format. */ /* Now pack it into the IDT entry in its weird format. */
idt->a = (LGUEST_CS<<16) | (handler&0x0000FFFF); idt->a = (LGUEST_CS<<16) | (handler&0x0000FFFF);
@ -428,7 +433,7 @@ void setup_default_idt_entries(struct lguest_ro_state *state,
unsigned int i; unsigned int i;
for (i = 0; i < ARRAY_SIZE(state->guest_idt); i++) for (i = 0; i < ARRAY_SIZE(state->guest_idt); i++)
default_idt_entry(&state->guest_idt[i], i, def[i]); default_idt_entry(&state->guest_idt[i], i, def[i], NULL);
} }
/*H:240 We don't use the IDT entries in the "struct lguest" directly, instead /*H:240 We don't use the IDT entries in the "struct lguest" directly, instead
@ -442,6 +447,8 @@ void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
/* We can simply copy the direct traps, otherwise we use the default /* We can simply copy the direct traps, otherwise we use the default
* ones in the Switcher: they will return to the Host. */ * ones in the Switcher: they will return to the Host. */
for (i = 0; i < ARRAY_SIZE(cpu->arch.idt); i++) { for (i = 0; i < ARRAY_SIZE(cpu->arch.idt); i++) {
const struct desc_struct *gidt = &cpu->arch.idt[i];
/* If no Guest can ever override this trap, leave it alone. */ /* If no Guest can ever override this trap, leave it alone. */
if (!direct_trap(i)) if (!direct_trap(i))
continue; continue;
@ -449,12 +456,15 @@ void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
/* Only trap gates (type 15) can go direct to the Guest. /* Only trap gates (type 15) can go direct to the Guest.
* Interrupt gates (type 14) disable interrupts as they are * Interrupt gates (type 14) disable interrupts as they are
* entered, which we never let the Guest do. Not present * entered, which we never let the Guest do. Not present
* entries (type 0x0) also can't go direct, of course. */ * entries (type 0x0) also can't go direct, of course.
if (idt_type(cpu->arch.idt[i].a, cpu->arch.idt[i].b) == 0xF) *
idt[i] = cpu->arch.idt[i]; * If it can't go direct, we still need to copy the priv. level:
* they might want to give userspace access to a software
* interrupt. */
if (idt_type(gidt->a, gidt->b) == 0xF)
idt[i] = *gidt;
else else
/* Reset it to the default. */ default_idt_entry(&idt[i], i, def[i], gidt);
default_idt_entry(&idt[i], i, def[i]);
} }
} }