From: Liran Alon <liran.alon@oracle.com>
Date: Thu, 8 Nov 2018 00:43:06 +0200
Subject: KVM: x86: Fix kernel info-leak in KVM_HC_CLOCK_PAIRING hypercall
Git-commit: bcbfbd8ec21096027f1ee13ce6c185e8175166f6
Patch-mainline: v4.20-rc5
References: bsc#1106240

kvm_pv_clock_pairing() allocates local var
"struct kvm_clock_pairing clock_pairing" on stack and initializes
all it's fields besides padding (clock_pairing.pad[]).

Because clock_pairing var is written completely (including padding)
to guest memory, failure to init struct padding results in kernel
info-leak.

Fix the issue by making sure to also init the padding with zeroes.

Fixes: 55dd00a73a51 ("KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall")
Reported-by: syzbot+a8ef68d71211ba264f56@syzkaller.appspotmail.com
Reviewed-by: Mark Kanda <mark.kanda@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kvm/x86.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 64cae03b2c20..7e4be1f2f253 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6918,6 +6918,7 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
 	clock_pairing.nsec = ts.tv_nsec;
 	clock_pairing.tsc = kvm_read_l1_tsc(vcpu, cycle);
 	clock_pairing.flags = 0;
+	memset(&clock_pairing.pad, 0, sizeof(clock_pairing.pad));
 
 	ret = 0;
 	if (kvm_write_guest(vcpu->kvm, paddr, &clock_pairing,