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[104.155.41.136]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45eaa7cf23bsm1764718f8f.5.2026.05.21.03.30.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2026 03:30:07 -0700 (PDT) Date: Thu, 21 May 2026 10:30:03 +0000 From: Mostafa Saleh To: Marc Zyngier Cc: op-tee@lists.trustedfirmware.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, jens.wiklander@linaro.org, sumit.garg@kernel.org, sebastianene@google.com, vdonnefort@google.com, sudeep.holla@kernel.org Subject: Re: [PATCH v4 4/5] KVM: arm64: Fix bounds checking in do_ffa_mem_reclaim() Message-ID: References: <20260520204948.2440882-1-smostafa@google.com> <20260520204948.2440882-5-smostafa@google.com> <86ldddw4ht.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86ldddw4ht.wl-maz@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260521_033011_168391_660B01A3 X-CRM114-Status: GOOD ( 28.32 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Marc, On Thu, May 21, 2026 at 09:28:46AM +0100, Marc Zyngier wrote: > On Wed, 20 May 2026 21:49:47 +0100, > Mostafa Saleh wrote: > > > > Sashiko (locally) reports out of bound write possiblity if SPMD > > returns an invalid data. > > > > While SPMD is considered trusted, pKVM does some basic checks, > > for offset to be less than or equal len. > > > > However, that is incorrect as even if the offset is smaller than > > len pKVM can still access out of bound memory in the next > > ffa_host_unshare_ranges(). > > > > Split this check into 2: > > 1- Check that the fixed portion of the descriptor fits. > > 2- After getting reg, check the variable array size addr_range_cnt > > fits. > > > > Signed-off-by: Mostafa Saleh > > --- > > arch/arm64/kvm/hyp/nvhe/ffa.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c > > index 1af722771178..e6aa2bfa63b1 100644 > > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c > > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c > > @@ -607,7 +607,7 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res, > > * check that we end up with something that doesn't look _completely_ > > * bogus. > > */ > > - if (WARN_ON(offset > len || > > + if (WARN_ON(offset + CONSTITUENTS_OFFSET(0) > len || > > fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE)) { > > Do you really want to keep this a WARN_ON(), given that this results > in a panic in most pKVM configurations? Which kind of configuration will that check fail on? Does that mean at the moment pKVM does out-of-bound access for the header? Thanks, Mostafa > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible.