[PATCH] KVM: arm64: Harden clock for nvhe/pKVM

[Mostafa Saleh <smostafa@google.com>]

Sashiko(locally) reports possiblity of division by zero and
out-of-bounds bitwise shift in trace_clock_update().

Although the clock update is untrusted, we should at least have some
basic checks to avoid the clock value getting out of sync if the host
is buggy.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 arch/arm64/kvm/hyp/nvhe/clock.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/clock.c b/arch/arm64/kvm/hyp/nvhe/clock.c
index 32fc4313fe43..a7fc61976fd0 100644
--- a/arch/arm64/kvm/hyp/nvhe/clock.c
+++ b/arch/arm64/kvm/hyp/nvhe/clock.c
@@ -35,6 +35,9 @@ void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
 	struct clock_data *clock = &trace_clock_data;
 	u64 bank = clock->cur ^ 1;
 
+	if (!mult || shift >= 64)
+		return;
+
 	clock->data[bank].mult			= mult;
 	clock->data[bank].shift			= shift;
 	clock->data[bank].epoch_ns		= epoch_ns;
-- 
2.54.0.545.g6539524ca2-goog