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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id q126sm21796589pfq.123.2019.07.02.14.03.36 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 02 Jul 2019 14:03:37 -0700 (PDT) Date: Tue, 2 Jul 2019 14:04:01 -0700 From: Nicolin Chen To: Robin Murphy Cc: Joerg Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] iommu/dma: Fix calculation overflow in __finalise_sg() Message-ID: <20190702210400.GA14593@Asurada-Nvidia.nvidia.com> References: <20190622043814.5003-1-nicoleotsuka@gmail.com> <20190701122158.GE8166@8bytes.org> <91a389be-fd76-c87f-7613-8cc972b69685@arm.com> <20190701215016.GA16247@Asurada-Nvidia.nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 02, 2019 at 11:40:02AM +0100, Robin Murphy wrote: > On reflection, I don't really think that size_t fits here anyway, since > all the members of the incoming struct scatterlist are unsigned int too. > Does the patch below work? Yes. > ----->8----- > From: Robin Murphy > Subject: [PATCH] iommu/dma: Handle SG length overflow better > > Since scatterlist dimensions are all unsigned ints, in the relatively > rare cases where a device's max_segment_size is set to UINT_MAX, then > the "cur_len + s_length <= max_len" check in __finalise_sg() will always > return true. As a result, the corner case of such a device mapping an > excessively large scatterlist which is mergeable to or beyond a total > length of 4GB can lead to overflow and a bogus truncated dma_length in > the resulting segment. > > As we already assume that any single segment must be no longer than > max_len to begin with, this can easily be addressed by reshuffling the > comparison. > > Fixes: 809eac54cdd6 ("iommu/dma: Implement scatterlist segment merging") > Reported-by: Nicolin Chen > Signed-off-by: Robin Murphy Tested-by: Nicolin Chen Thank you! > --- > drivers/iommu/dma-iommu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index 129c4badf9ae..8de6cf623362 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -721,7 +721,7 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, > * - and wouldn't make the resulting output segment too long > */ > if (cur_len && !s_iova_off && (dma_addr & seg_mask) && > - (cur_len + s_length <= max_len)) { > + (max_len - cur_len >= s_length)) { > /* ...then concatenate it with the previous one */ > cur_len += s_length; > } else {