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[146.148.11.143]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490ea7db9c6sm71157125e9.8.2026.06.12.07.22.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Jun 2026 07:22:29 -0700 (PDT) Date: Fri, 12 Jun 2026 14:22:25 +0000 From: Sebastian Ene To: Mostafa Saleh Cc: op-tee@lists.trustedfirmware.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, jens.wiklander@linaro.org, sumit.garg@kernel.org, vdonnefort@google.com, sudeep.holla@kernel.org Subject: Re: [PATCH v6 4/6] KVM: arm64: Fix bounds checking in do_ffa_mem_reclaim() Message-ID: References: <20260527150236.1978655-1-smostafa@google.com> <20260527150236.1978655-5-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: <20260527150236.1978655-5-smostafa@google.com> On Wed, May 27, 2026 at 03:02:34PM +0000, 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. > > Also, drop the WARN_ONs as that will panic the kernel and in the > next checks there are no WARNs, so that makes it consistent. > > Fixes: 0a9f15fd5674 ("KVM: arm64: pkvm: Add support for fragmented FF-A descriptors") > Signed-off-by: Mostafa Saleh > --- > arch/arm64/kvm/hyp/nvhe/ffa.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c > index 1af722771178..b6cf9ad82e12 100644 > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c > @@ -607,8 +607,8 @@ 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 || > - fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE)) { > + if (offset + CONSTITUENTS_OFFSET(0) > len || > + fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) { > ret = FFA_RET_ABORTED; > ffa_rx_release(res); > goto out_unlock; > @@ -641,6 +641,11 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res, > goto out_unlock; > > reg = (void *)buf + offset; > + if (offset + CONSTITUENTS_OFFSET(reg->addr_range_cnt) > len) { > + ret = FFA_RET_ABORTED; > + goto out_unlock; > + } > + I wonder if we should do this check first and then mem_reclaim, the rational being that if the check fails the page will be lost forever. ``` reg = (void *)buf + offset; if (offset + CONSTITUENTS_OFFSET(reg->addr_range_cnt) > len) { ret = FFA_RET_ABORTED; goto out_unlock; } ffa_mem_reclaim(res, handle_lo, handle_hi, flags); if (res->a0 != FFA_SUCCESS) goto out_unlock; ``` > /* If the SPMD was happy, then we should be too. */ > WARN_ON(ffa_host_unshare_ranges(reg->constituents, > reg->addr_range_cnt)); > -- > 2.54.0.746.g67dd491aae-goog > Sebastian