Back link is written to a wrong TSS now.
Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 40 ++++++++++++++++++++++++++++++++--------
1 files changed, 32 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ae4918c..f14c622 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3697,7 +3697,6 @@ static void save_state_to_tss32(struct kvm_vcpu *vcpu,
tss->fs = get_segment_selector(vcpu, VCPU_SREG_FS);
tss->gs = get_segment_selector(vcpu, VCPU_SREG_GS);
tss->ldt_selector = get_segment_selector(vcpu, VCPU_SREG_LDTR);
- tss->prev_task_link = get_segment_selector(vcpu, VCPU_SREG_TR);
}
static int load_state_from_tss32(struct kvm_vcpu *vcpu,
@@ -3794,8 +3793,8 @@ static int load_state_from_tss16(struct kvm_vcpu *vcpu,
}
static int kvm_task_switch_16(struct kvm_vcpu *vcpu, u16 tss_selector,
- u32 old_tss_base,
- struct desc_struct *nseg_desc)
+ u16 old_tss_sel, u32 old_tss_base,
+ struct desc_struct *nseg_desc)
{
struct tss_segment_16 tss_segment_16;
int ret = 0;
@@ -3814,6 +3813,16 @@ static int kvm_task_switch_16(struct kvm_vcpu *vcpu, u16 tss_selector,
&tss_segment_16, sizeof tss_segment_16))
goto out;
+ if (old_tss_sel != 0xffff) {
+ tss_segment_16.prev_task_link = old_tss_sel;
+
+ if (kvm_write_guest(vcpu->kvm,
+ get_tss_base_addr(vcpu, nseg_desc),
+ &tss_segment_16.prev_task_link,
+ sizeof tss_segment_16.prev_task_link))
+ goto out;
+ }
+
if (load_state_from_tss16(vcpu, &tss_segment_16))
goto out;
@@ -3823,7 +3832,7 @@ out:
}
static int kvm_task_switch_32(struct kvm_vcpu *vcpu, u16 tss_selector,
- u32 old_tss_base,
+ u16 old_tss_sel, u32 old_tss_base,
struct desc_struct *nseg_desc)
{
struct tss_segment_32 tss_segment_32;
@@ -3843,6 +3852,16 @@ static int kvm_task_switch_32(struct kvm_vcpu *vcpu, u16 tss_selector,
&tss_segment_32, sizeof tss_segment_32))
goto out;
+ if (old_tss_sel != 0xffff) {
+ tss_segment_32.prev_task_link = old_tss_sel;
+
+ if (kvm_write_guest(vcpu->kvm,
+ get_tss_base_addr(vcpu, nseg_desc),
+ &tss_segment_32.prev_task_link,
+ sizeof tss_segment_32.prev_task_link))
+ goto out;
+ }
+
if (load_state_from_tss32(vcpu, &tss_segment_32))
goto out;
@@ -3898,12 +3917,17 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
kvm_x86_ops->skip_emulated_instruction(vcpu);
+ /* set back link to prev task only if NT bit is set in eflags
+ note that old_tss_sel is not used afetr this point */
+ if (reason != TASK_SWITCH_CALL && reason != TASK_SWITCH_GATE)
+ old_tss_sel = 0xffff;
+
if (nseg_desc.type & 8)
- ret = kvm_task_switch_32(vcpu, tss_selector, old_tss_base,
- &nseg_desc);
+ ret = kvm_task_switch_32(vcpu, tss_selector, old_tss_sel,
+ old_tss_base, &nseg_desc);
else
- ret = kvm_task_switch_16(vcpu, tss_selector, old_tss_base,
- &nseg_desc);
+ ret = kvm_task_switch_16(vcpu, tss_selector, old_tss_sel,
+ old_tss_base, &nseg_desc);
if (reason == TASK_SWITCH_CALL || reason == TASK_SWITCH_GATE) {
u32 eflags = kvm_x86_ops->get_rflags(vcpu);
--
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