[PATCH 3/3] KVM: x86: Fix broken debugregs ABI for 32 bit kernels

[Mathias Krause <minipli@xxxxxxxxxxxxxx>]

The ioctl()s to get and set KVM's debug registers are broken for 32 bit
kernels as they'd only copy half of the user register state because of a
UAPI and in-kernel type mismatch (__u64 vs. unsigned long; 8 vs. 4
bytes).

This makes it impossible for userland to set anything but DR0 without
resorting to bit folding tricks.

Switch to a loop for copying debug registers that'll implicitly do the
type conversion for us, if needed.

There are likely no users (left) for 32bit KVM, fix the bug nonetheless.

Fixes: a1efbe77c1fd ("KVM: x86: Add support for saving&restoring debug registers")
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0f958dcf8458..34ea934b499b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5504,8 +5504,14 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 					     struct kvm_debugregs *dbgregs)
 {
+	unsigned int i;
+
 	memset(dbgregs, 0, sizeof(*dbgregs));
-	memcpy(dbgregs->db, vcpu->arch.db, sizeof(vcpu->arch.db));
+
+	BUILD_BUG_ON(ARRAY_SIZE(vcpu->arch.db) != ARRAY_SIZE(dbgregs->db));
+	for (i = 0; i < ARRAY_SIZE(vcpu->arch.db); i++)
+		dbgregs->db[i] = vcpu->arch.db[i];
+
 	dbgregs->dr6 = vcpu->arch.dr6;
 	dbgregs->dr7 = vcpu->arch.dr7;
 }
@@ -5513,6 +5519,8 @@ static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 					    struct kvm_debugregs *dbgregs)
 {
+	unsigned int i;
+
 	if (dbgregs->flags)
 		return -EINVAL;
 
@@ -5521,7 +5529,9 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 	if (!kvm_dr7_valid(dbgregs->dr7))
 		return -EINVAL;
 
-	memcpy(vcpu->arch.db, dbgregs->db, sizeof(vcpu->arch.db));
+	for (i = 0; i < ARRAY_SIZE(vcpu->arch.db); i++)
+		vcpu->arch.db[i] = dbgregs->db[i];
+
 	kvm_update_dr0123(vcpu);
 	vcpu->arch.dr6 = dbgregs->dr6;
 	vcpu->arch.dr7 = dbgregs->dr7;
-- 
2.39.2