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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id x6sm107467pge.61.2020.08.20.16.20.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Aug 2020 16:20:19 -0700 (PDT) From: Nicolin Chen To: rth@twiddle.net, ink@jurassic.park.msu.ru, mattst88@gmail.com Cc: hch@lst.de, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFT][PATCH 2/7] alpha: Avoid overflow at boundary_size Date: Thu, 20 Aug 2020 16:20:04 -0700 Message-Id: <20200820232004.23761-1-nicoleotsuka@gmail.com> X-Mailer: git-send-email 2.17.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The boundary_size might be as large as ULONG_MAX, which means that a device has no specific boundary limit. So "+ 1" would potentially overflow. Also, by following other places in the kernel, boundary_size should align with the PAGE_SIZE before right shifting by the PAGE_SHIFT. However, passing it to ALIGN() would potentially overflow too. 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. Signed-off-by: Nicolin Chen Cc: Christoph Hellwig --- arch/alpha/kernel/pci_iommu.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/arch/alpha/kernel/pci_iommu.c b/arch/alpha/kernel/pci_iommu.c index 81037907268d..1ef2c647bd3e 100644 --- a/arch/alpha/kernel/pci_iommu.c +++ b/arch/alpha/kernel/pci_iommu.c @@ -141,12 +141,10 @@ iommu_arena_find_pages(struct device *dev, struct pci_iommu_arena *arena, unsigned long boundary_size; base = arena->dma_base >> PAGE_SHIFT; - if (dev) { - boundary_size = dma_get_seg_boundary(dev) + 1; - boundary_size >>= PAGE_SHIFT; - } else { - boundary_size = 1UL << (32 - PAGE_SHIFT); - } + + boundary_size = dev ? dma_get_seg_boundary(dev) : U32_MAX; + /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */ + boundary_size = (boundary_size >> PAGE_SHIFT) + 1; /* Search forward for the first mask-aligned sequence of N free ptes */ ptes = arena->ptes; -- 2.17.1