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KVM: x86: Rework guest single-step flag injection and filtering
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Push TF and RF injection and filtering on guest single-stepping into the
vender get/set_rflags callbacks. This makes the whole mechanism more
robust wrt user space IOCTL order and instruction emulations.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
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Jan Kiszka authored and Avi Kivity committed Dec 3, 2009
1 parent a68a6a7 commit 91586a3
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Showing 2 changed files with 48 additions and 32 deletions.
3 changes: 3 additions & 0 deletions arch/x86/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -614,6 +614,9 @@ void kvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l);
int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata);
int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data);

unsigned long kvm_get_rflags(struct kvm_vcpu *vcpu);
void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);

void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr);
void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code);
void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long cr2,
Expand Down
77 changes: 45 additions & 32 deletions arch/x86/kvm/x86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -235,6 +235,25 @@ bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl)
}
EXPORT_SYMBOL_GPL(kvm_require_cpl);

unsigned long kvm_get_rflags(struct kvm_vcpu *vcpu)
{
unsigned long rflags;

rflags = kvm_x86_ops->get_rflags(vcpu);
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
rflags &= ~(unsigned long)(X86_EFLAGS_TF | X86_EFLAGS_RF);
return rflags;
}
EXPORT_SYMBOL_GPL(kvm_get_rflags);

void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
{
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
rflags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
kvm_x86_ops->set_rflags(vcpu, rflags);
}
EXPORT_SYMBOL_GPL(kvm_set_rflags);

/*
* Load the pae pdptrs. Return true is they are all valid.
*/
Expand Down Expand Up @@ -2777,7 +2796,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);

vcpu->arch.emulate_ctxt.vcpu = vcpu;
vcpu->arch.emulate_ctxt.eflags = kvm_x86_ops->get_rflags(vcpu);
vcpu->arch.emulate_ctxt.eflags = kvm_get_rflags(vcpu);
vcpu->arch.emulate_ctxt.mode =
(vcpu->arch.emulate_ctxt.eflags & X86_EFLAGS_VM)
? X86EMUL_MODE_REAL : cs_l
Expand Down Expand Up @@ -2855,7 +2874,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
return EMULATE_DO_MMIO;
}

kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
kvm_set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);

if (vcpu->mmio_is_write) {
vcpu->mmio_needed = 0;
Expand Down Expand Up @@ -3291,7 +3310,7 @@ void realmode_lmsw(struct kvm_vcpu *vcpu, unsigned long msw,
unsigned long *rflags)
{
kvm_lmsw(vcpu, msw);
*rflags = kvm_x86_ops->get_rflags(vcpu);
*rflags = kvm_get_rflags(vcpu);
}

unsigned long realmode_get_cr(struct kvm_vcpu *vcpu, int cr)
Expand Down Expand Up @@ -3329,7 +3348,7 @@ void realmode_set_cr(struct kvm_vcpu *vcpu, int cr, unsigned long val,
switch (cr) {
case 0:
kvm_set_cr0(vcpu, mk_cr_64(vcpu->arch.cr0, val));
*rflags = kvm_x86_ops->get_rflags(vcpu);
*rflags = kvm_get_rflags(vcpu);
break;
case 2:
vcpu->arch.cr2 = val;
Expand Down Expand Up @@ -3460,7 +3479,7 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu)
{
struct kvm_run *kvm_run = vcpu->run;

kvm_run->if_flag = (kvm_x86_ops->get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
kvm_run->if_flag = (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
kvm_run->cr8 = kvm_get_cr8(vcpu);
kvm_run->apic_base = kvm_get_apic_base(vcpu);
if (irqchip_in_kernel(vcpu->kvm))
Expand Down Expand Up @@ -3840,13 +3859,7 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
#endif

regs->rip = kvm_rip_read(vcpu);
regs->rflags = kvm_x86_ops->get_rflags(vcpu);

/*
* Don't leak debug flags in case they were set for guest debugging
*/
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
regs->rflags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
regs->rflags = kvm_get_rflags(vcpu);

vcpu_put(vcpu);

Expand Down Expand Up @@ -3874,12 +3887,10 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
kvm_register_write(vcpu, VCPU_REGS_R13, regs->r13);
kvm_register_write(vcpu, VCPU_REGS_R14, regs->r14);
kvm_register_write(vcpu, VCPU_REGS_R15, regs->r15);

#endif

kvm_rip_write(vcpu, regs->rip);
kvm_x86_ops->set_rflags(vcpu, regs->rflags);

kvm_set_rflags(vcpu, regs->rflags);

vcpu->arch.exception.pending = false;

Expand Down Expand Up @@ -4098,7 +4109,7 @@ static int is_vm86_segment(struct kvm_vcpu *vcpu, int seg)
{
return (seg != VCPU_SREG_LDTR) &&
(seg != VCPU_SREG_TR) &&
(kvm_x86_ops->get_rflags(vcpu) & X86_EFLAGS_VM);
(kvm_get_rflags(vcpu) & X86_EFLAGS_VM);
}

int kvm_load_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
Expand Down Expand Up @@ -4126,7 +4137,7 @@ static void save_state_to_tss32(struct kvm_vcpu *vcpu,
{
tss->cr3 = vcpu->arch.cr3;
tss->eip = kvm_rip_read(vcpu);
tss->eflags = kvm_x86_ops->get_rflags(vcpu);
tss->eflags = kvm_get_rflags(vcpu);
tss->eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
tss->ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
tss->edx = kvm_register_read(vcpu, VCPU_REGS_RDX);
Expand All @@ -4150,7 +4161,7 @@ static int load_state_from_tss32(struct kvm_vcpu *vcpu,
kvm_set_cr3(vcpu, tss->cr3);

kvm_rip_write(vcpu, tss->eip);
kvm_x86_ops->set_rflags(vcpu, tss->eflags | 2);
kvm_set_rflags(vcpu, tss->eflags | 2);

kvm_register_write(vcpu, VCPU_REGS_RAX, tss->eax);
kvm_register_write(vcpu, VCPU_REGS_RCX, tss->ecx);
Expand Down Expand Up @@ -4188,7 +4199,7 @@ static void save_state_to_tss16(struct kvm_vcpu *vcpu,
struct tss_segment_16 *tss)
{
tss->ip = kvm_rip_read(vcpu);
tss->flag = kvm_x86_ops->get_rflags(vcpu);
tss->flag = kvm_get_rflags(vcpu);
tss->ax = kvm_register_read(vcpu, VCPU_REGS_RAX);
tss->cx = kvm_register_read(vcpu, VCPU_REGS_RCX);
tss->dx = kvm_register_read(vcpu, VCPU_REGS_RDX);
Expand All @@ -4209,7 +4220,7 @@ static int load_state_from_tss16(struct kvm_vcpu *vcpu,
struct tss_segment_16 *tss)
{
kvm_rip_write(vcpu, tss->ip);
kvm_x86_ops->set_rflags(vcpu, tss->flag | 2);
kvm_set_rflags(vcpu, tss->flag | 2);
kvm_register_write(vcpu, VCPU_REGS_RAX, tss->ax);
kvm_register_write(vcpu, VCPU_REGS_RCX, tss->cx);
kvm_register_write(vcpu, VCPU_REGS_RDX, tss->dx);
Expand Down Expand Up @@ -4355,8 +4366,8 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
}

if (reason == TASK_SWITCH_IRET) {
u32 eflags = kvm_x86_ops->get_rflags(vcpu);
kvm_x86_ops->set_rflags(vcpu, eflags & ~X86_EFLAGS_NT);
u32 eflags = kvm_get_rflags(vcpu);
kvm_set_rflags(vcpu, eflags & ~X86_EFLAGS_NT);
}

/* set back link to prev task only if NT bit is set in eflags
Expand All @@ -4377,8 +4388,8 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
old_tss_base, &nseg_desc);

if (reason == TASK_SWITCH_CALL || reason == TASK_SWITCH_GATE) {
u32 eflags = kvm_x86_ops->get_rflags(vcpu);
kvm_x86_ops->set_rflags(vcpu, eflags | X86_EFLAGS_NT);
u32 eflags = kvm_get_rflags(vcpu);
kvm_set_rflags(vcpu, eflags | X86_EFLAGS_NT);
}

if (reason != TASK_SWITCH_IRET) {
Expand Down Expand Up @@ -4473,12 +4484,15 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
{
unsigned long rflags;
int old_debug;
int i;

vcpu_load(vcpu);

old_debug = vcpu->guest_debug;
/*
* Read rflags as long as potentially injected trace flags are still
* filtered out.
*/
rflags = kvm_get_rflags(vcpu);

vcpu->guest_debug = dbg->control;
if (!(vcpu->guest_debug & KVM_GUESTDBG_ENABLE))
Expand All @@ -4495,12 +4509,11 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
vcpu->arch.switch_db_regs = (vcpu->arch.dr7 & DR7_BP_EN_MASK);
}

rflags = kvm_x86_ops->get_rflags(vcpu);
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
rflags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
else if (old_debug & KVM_GUESTDBG_SINGLESTEP)
rflags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
kvm_x86_ops->set_rflags(vcpu, rflags);
/*
* Trigger an rflags update that will inject or remove the trace
* flags.
*/
kvm_set_rflags(vcpu, rflags);

kvm_x86_ops->set_guest_debug(vcpu, dbg);

Expand Down

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