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KVM: x86: Honor KVM_GUESTDBG_USE_HW_BP when emulating MOV DR (in emulator)

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When emulating a MOV DR instruction, honor KVM_GUESTDBG_USE_HW_BP when
checking DR7.GD, and if there is a general-detect #DB, route it to host
userspace as appropriate.  Consulting only the guest's actual DR7 causes
KVM to fail to report a DR access to userspace (assuming the guest itself
doesn't have DR7.GD=1).

Fixes: ae675ef01c ("KVM: x86: Wire-up hardware breakpoints for guest debugging")
Suggested-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
[sean: only expose effective DR7 to emulator, massage changelog]
Link: https://patch.msgid.link/20260515222638.1949982-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Hou Wenlong 2026-05-15 15:26:32 -07:00 committed by Sean Christopherson
parent dfc1c4687e
commit 51543660c5
3 changed files with 35 additions and 9 deletions
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2
arch/x86/kvm/emulate.c
View File

@ -3848,7 +3848,7 @@ static int check_dr_read(struct x86_emulate_ctxt *ctxt)
if ((cr4 & X86_CR4_DE) && (dr == 4 || dr == 5))
return emulate_ud(ctxt);
if (ctxt->ops->get_dr(ctxt, 7) & DR7_GD)
if (ctxt->ops->get_effective_dr7(ctxt) & DR7_GD)
return emulate_db(ctxt, DR6_BD);
return X86EMUL_CONTINUE;

1
arch/x86/kvm/kvm_emulate.h
View File

@ -215,6 +215,7 @@ struct x86_emulate_ops {
ulong (*get_cr)(struct x86_emulate_ctxt *ctxt, int cr);
int (*set_cr)(struct x86_emulate_ctxt *ctxt, int cr, ulong val);
int (*cpl)(struct x86_emulate_ctxt *ctxt);
ulong (*get_effective_dr7)(struct x86_emulate_ctxt *ctxt);
ulong (*get_dr)(struct x86_emulate_ctxt *ctxt, int dr);
int (*set_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong value);
int (*set_msr_with_filter)(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 data);

41
arch/x86/kvm/x86.c
View File

@ -1606,6 +1606,14 @@ unsigned long kvm_get_dr(struct kvm_vcpu *vcpu, int dr)
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_get_dr);
static unsigned long kvm_get_effective_dr7(struct kvm_vcpu *vcpu)
{
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
return vcpu->arch.guest_debug_dr7;
return vcpu->arch.dr7;
}
int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu)
{
u32 pmc = kvm_rcx_read(vcpu);
@ -8549,6 +8557,11 @@ static void emulator_wbinvd(struct x86_emulate_ctxt *ctxt)
kvm_emulate_wbinvd_noskip(emul_to_vcpu(ctxt));
}
static unsigned long emulator_get_effective_dr7(struct x86_emulate_ctxt *ctxt)
{
return kvm_get_effective_dr7(emul_to_vcpu(ctxt));
}
static unsigned long emulator_get_dr(struct x86_emulate_ctxt *ctxt, int dr)
{
return kvm_get_dr(emul_to_vcpu(ctxt), dr);
@ -8931,6 +8944,7 @@ static const struct x86_emulate_ops emulate_ops = {
.get_cr = emulator_get_cr,
.set_cr = emulator_set_cr,
.cpl = emulator_get_cpl,
.get_effective_dr7 = emulator_get_effective_dr7,
.get_dr = emulator_get_dr,
.set_dr = emulator_set_dr,
.set_msr_with_filter = emulator_set_msr_with_filter,
@ -8977,23 +8991,36 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
}
}
static void kvm_inject_emulated_db(struct kvm_vcpu *vcpu, unsigned long dr6)
static int kvm_inject_emulated_db(struct kvm_vcpu *vcpu, unsigned long dr6)
{
struct kvm_run *kvm_run = vcpu->run;
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
kvm_run->debug.arch.dr6 = dr6 | DR6_ACTIVE_LOW;
kvm_run->debug.arch.pc = kvm_get_linear_rip(vcpu);
kvm_run->debug.arch.exception = DB_VECTOR;
kvm_run->exit_reason = KVM_EXIT_DEBUG;
return 0;
}
kvm_queue_exception_p(vcpu, DB_VECTOR, dr6);
return 1;
}
static void inject_emulated_exception(struct kvm_vcpu *vcpu)
static int inject_emulated_exception(struct kvm_vcpu *vcpu)
{
struct x86_exception *ex = &vcpu->arch.emulate_ctxt->exception;
if (ex->vector == DB_VECTOR)
kvm_inject_emulated_db(vcpu, ex->dr6);
else if (ex->vector == PF_VECTOR)
return kvm_inject_emulated_db(vcpu, ex->dr6);
if (ex->vector == PF_VECTOR)
kvm_inject_emulated_page_fault(vcpu, ex);
else if (ex->error_code_valid)
kvm_queue_exception_e(vcpu, ex->vector, ex->error_code);
else
kvm_queue_exception(vcpu, ex->vector);
return 1;
}
static struct x86_emulate_ctxt *alloc_emulate_ctxt(struct kvm_vcpu *vcpu)
@ -9502,8 +9529,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
*/
WARN_ON_ONCE(ctxt->exception.vector == UD_VECTOR ||
exception_type(ctxt->exception.vector) == EXCPT_TRAP);
inject_emulated_exception(vcpu);
return 1;
return inject_emulated_exception(vcpu);
}
return handle_emulation_failure(vcpu, emulation_type);
}
@ -9598,8 +9624,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
if (ctxt->have_exception) {
WARN_ON_ONCE(vcpu->mmio_needed && !vcpu->mmio_is_write);
vcpu->mmio_needed = false;
r = 1;
inject_emulated_exception(vcpu);
r = inject_emulated_exception(vcpu);
} else if (vcpu->arch.pio.count) {
if (!vcpu->arch.pio.in) {
/* FIXME: return into emulator if single-stepping. */