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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id e29sm154527pfj.92.2020.08.20.16.20.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Aug 2020 16:20:05 -0700 (PDT) From: Nicolin Chen To: mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org Cc: sfr@canb.auug.org.au, hch@lst.de, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: [RFT][PATCH 1/7] powerpc/iommu: Avoid overflow at boundary_size Date: Thu, 20 Aug 2020 16:19:50 -0700 Message-Id: <20200820231950.23719-1-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 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(-) 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; + + /* 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