From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728989AbgHaUiw (ORCPT ); Mon, 31 Aug 2020 16:38:52 -0400 From: Nicolin Chen Subject: [RESEND][PATCH 6/7] x86/amd_gart: Avoid overflow at boundary_size Date: Mon, 31 Aug 2020 13:38:10 -0700 Message-Id: <20200831203811.8494-7-nicoleotsuka@gmail.com> In-Reply-To: <20200831203811.8494-1-nicoleotsuka@gmail.com> References: <20200831203811.8494-1-nicoleotsuka@gmail.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org, rth@twiddle.net, ink@jurassic.park.msu.ru, mattst88@gmail.com, tony.luck@intel.com, fenghua.yu@intel.com, schnelle@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, James.Bottomley@HansenPartnership.com, deller@gmx.de Cc: sfr@canb.auug.org.au, hch@lst.de, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-parisc@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. Signed-off-by: Nicolin Chen Cc: Christoph Hellwig --- arch/x86/kernel/amd_gart_64.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/amd_gart_64.c b/arch/x86/kernel/amd_gart_64.c index e89031e9c847..7fa0bb490065 100644 --- a/arch/x86/kernel/amd_gart_64.c +++ b/arch/x86/kernel/amd_gart_64.c @@ -96,8 +96,8 @@ static unsigned long alloc_iommu(struct device *dev, int size, base_index = ALIGN(iommu_bus_base & dma_get_seg_boundary(dev), PAGE_SIZE) >> PAGE_SHIFT; - boundary_size = ALIGN((u64)dma_get_seg_boundary(dev) + 1, - PAGE_SIZE) >> PAGE_SHIFT; + /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */ + boundary_size = (dma_get_seg_boundary(dev) >> PAGE_SHIFT) + 1; spin_lock_irqsave(&iommu_bitmap_lock, flags); offset = iommu_area_alloc(iommu_gart_bitmap, iommu_pages, next_bit, -- 2.17.1