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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id y1sm3016263pgr.3.2020.09.01.13.54.20 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Tue, 01 Sep 2020 13:54:21 -0700 (PDT) Date: Tue, 1 Sep 2020 13:53:47 -0700 From: Nicolin Chen To: Michael Ellerman Subject: Re: [RESEND][PATCH 1/7] powerpc/iommu: Avoid overflow at boundary_size Message-ID: <20200901205346.GA17362@Asurada-Nvidia> References: <20200831203811.8494-1-nicoleotsuka@gmail.com> <20200831203811.8494-2-nicoleotsuka@gmail.com> <87lfht1vav.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87lfht1vav.fsf@mpe.ellerman.id.au> User-Agent: Mutt/1.9.4 (2018-02-28) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, James.Bottomley@HansenPartnership.com, paulus@samba.org, hpa@zytor.com, sparclinux@vger.kernel.org, hch@lst.de, sfr@canb.auug.org.au, deller@gmx.de, x86@kernel.org, borntraeger@de.ibm.com, mingo@redhat.com, mattst88@gmail.com, fenghua.yu@intel.com, gor@linux.ibm.com, schnelle@linux.ibm.com, hca@linux.ibm.com, ink@jurassic.park.msu.ru, tglx@linutronix.de, gerald.schaefer@linux.ibm.com, rth@twiddle.net, tony.luck@intel.com, linux-parisc@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, bp@alien8.de, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Sep 01, 2020 at 11:27:36PM +1000, Michael Ellerman wrote: > Nicolin Chen writes: > > The boundary_size might be as large as ULONG_MAX, which means > > that a device has no specific boundary limit. So either "+ 1" > > or passing it to ALIGN() would potentially overflow. > > > > According to kernel defines: > > #define ALIGN_MASK(x, mask) (((x) + (mask)) & ~(mask)) > > #define ALIGN(x, a) ALIGN_MASK(x, (typeof(x))(a) - 1) > > > > We can simplify the logic here: > > ALIGN(boundary + 1, 1 << shift) >> shift > > = ALIGN_MASK(b + 1, (1 << s) - 1) >> s > > = {[b + 1 + (1 << s) - 1] & ~[(1 << s) - 1]} >> s > > = [b + 1 + (1 << s) - 1] >> s > > = [b + (1 << s)] >> s > > = (b >> s) + 1 > > > > So fixing a potential overflow with the safer shortcut. > > > > Reported-by: Stephen Rothwell > > Signed-off-by: Nicolin Chen > > Cc: Christoph Hellwig > > --- > > arch/powerpc/kernel/iommu.c | 11 +++++------ > > 1 file changed, 5 insertions(+), 6 deletions(-) > > Are you asking for acks, or for maintainers to merge the patches > individually? I was expecting that but Christoph just suggested me to squash them into one so he would merge it: https://lkml.org/lkml/2020/9/1/159 Though I feel it'd be nice to get maintainers' acks before merging. > > diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c > > index 9704f3f76e63..c01ccbf8afdd 100644 > > --- a/arch/powerpc/kernel/iommu.c > > +++ b/arch/powerpc/kernel/iommu.c > > @@ -236,15 +236,14 @@ static unsigned long iommu_range_alloc(struct device *dev, > > } > > } > > > > - if (dev) > > - boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1, > > - 1 << tbl->it_page_shift); > > - else > > - boundary_size = ALIGN(1UL << 32, 1 << tbl->it_page_shift); > > /* 4GB boundary for iseries_hv_alloc and iseries_hv_map */ > > + boundary_size = dev ? dma_get_seg_boundary(dev) : U32_MAX; > > Is there any path that passes a NULL dev anymore? > > Both iseries_hv_alloc() and iseries_hv_map() were removed years ago. > See: > 8ee3e0d69623 ("powerpc: Remove the main legacy iSerie platform code") > > > So maybe we should do a lead-up patch that drops the NULL dev support, > which will then make this patch simpler. The next version of this change will follow Christoph's suggestion by having a helper function that takes care of !dev internally. Thanks Nic > > > > + /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */ > > + boundary_size = (boundary_size >> tbl->it_page_shift) + 1; > > > > n = iommu_area_alloc(tbl->it_map, limit, start, npages, tbl->it_offset, > > - boundary_size >> tbl->it_page_shift, align_mask); > > + boundary_size, align_mask); > > if (n == -1) { > > if (likely(pass == 0)) { > > /* First try the pool from the start */ > > -- > > 2.17.1