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[34.140.183.197]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-450524834eesm12653531f8f.4.2026.05.06.08.03.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 May 2026 08:03:46 -0700 (PDT) Date: Wed, 6 May 2026 16:03:43 +0100 From: Vincent Donnefort To: Mostafa Saleh Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, catalin.marinas@arm.com, will@kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, tabba@google.com Subject: Re: [PATCH] KVM: arm64: Harden clock for nvhe/pKVM Message-ID: References: <20260430103724.2151625-1-smostafa@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260430103724.2151625-1-smostafa@google.com> On Thu, Apr 30, 2026 at 10:37:24AM +0000, Mostafa Saleh wrote: > 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. I am not sure about the gain here. The host can still write values that will make it out of sync anyway. The timestamp is ultimately fed and read by the host. > > Signed-off-by: Mostafa Saleh > --- > 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 >