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[34.22.131.218]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-427f00b97f8sm25217515f8f.36.2025.10.22.08.21.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Oct 2025 08:21:44 -0700 (PDT) Date: Wed, 22 Oct 2025 16:21:41 +0100 From: Vincent Donnefort To: Sebastian Ene Cc: maz@kernel.org, oliver.upton@linux.dev, will@kernel.org, catalin.marinas@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, joey.gouly@arm.com, ayrton@google.com, yuzenghui@huawei.com, qperret@google.com, kernel-team@android.com Subject: Re: [PATCH] KVM: arm64: Check the untrusted offset in FF-A memory share Message-ID: References: <20251017075710.2605118-1-sebastianene@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: <20251017075710.2605118-1-sebastianene@google.com> On Fri, Oct 17, 2025 at 07:57:10AM +0000, Sebastian Ene wrote: > Verify the offset to prevent OOB access in the hypervisor I believe that would be just a read, so probably it would be difficult to use this to compromise anything, except crashing the system? > FF-A buffer in case an untrusted large enough value > [U32_MAX - sizeof(struct ffa_composite_mem_region) + 1, U32_MAX] > is set from the host kernel. > > Signed-off-by: Sebastian Ene > --- > 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 4e16f9b96f63..58b7d0c477d7 100644 > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c > @@ -479,7 +479,7 @@ static void __do_ffa_mem_xfer(const u64 func_id, > struct ffa_mem_region_attributes *ep_mem_access; > struct ffa_composite_mem_region *reg; > struct ffa_mem_region *buf; > - u32 offset, nr_ranges; > + u32 offset, nr_ranges, checked_offset; > int ret = 0; > > if (addr_mbz || npages_mbz || fraglen > len || > @@ -516,7 +516,12 @@ static void __do_ffa_mem_xfer(const u64 func_id, > goto out_unlock; > } > > - if (fraglen < offset + sizeof(struct ffa_composite_mem_region)) { > + if (check_add_overflow(offset, sizeof(struct ffa_composite_mem_region), &checked_offset)) { > + ret = FFA_RET_INVALID_PARAMETERS; > + goto out_unlock; > + } > + > + if (fraglen < checked_offset) { > ret = FFA_RET_INVALID_PARAMETERS; > goto out_unlock; > Perhaps this could be easier to reason about by moving this check with the nr_ranges? reg = (void *)buf + offset; if ((void *)reg->constituents > (void *)buf + fraglen) { ret = FFA_RET_INVALID_PARAMETERS; goto out_unlock; } nr_ranges = ((void *)buf + fraglen) - (void *)reg->constituents; if (nr_ranges % sizeof(reg->constituents[0])) { ret = FFA_RET_INVALID_PARAMETERS; } > -- > 2.51.0.858.gf9c4a03a3a-goog >