kvm: initialize all of the kvm_debugregs structure before sending it to userspace

stable inclusion
from stable-v5.10.169
commit 6416c2108ba54d569e4c98d3b62ac78cb12e7107
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6OOP3
CVE: CVE-2023-1513

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6416c2108ba54d569e4c98d3b62ac78cb12e7107

--------------------------------

commit 2c10b614 upstream.

When calling the KVM_GET_DEBUGREGS ioctl, on some configurations, there
might be some unitialized portions of the kvm_debugregs structure that
could be copied to userspace.  Prevent this as is done in the other kvm
ioctls, by setting the whole structure to 0 before copying anything into
it.

Bonus is that this reduces the lines of code as the explicit flag
setting and reserved space zeroing out can be removed.

Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <x86@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: stable <stable@kernel.org>
Reported-by: NXingyuan Mo <hdthky0@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Message-Id: <20230214103304.3689213-1-gregkh@linuxfoundation.org>
Tested-by: NXingyuan Mo <hdthky0@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NGuo Mengqi <guomengqi3@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

arch/x86/kvm/x86.c

@@ -4517,12 +4517,11 @@ static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 {
 	unsigned long val;
 
+	memset(dbgregs, 0, sizeof(*dbgregs));
 	memcpy(dbgregs->db, vcpu->arch.db, sizeof(vcpu->arch.db));
 	kvm_get_dr(vcpu, 6, &val);
 	dbgregs->dr6 = val;
 	dbgregs->dr7 = vcpu->arch.dr7;
-	dbgregs->flags = 0;
-	memset(&dbgregs->reserved, 0, sizeof(dbgregs->reserved));
 }
 
 static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,