linux-kernel - [RFT][PATCH 0/7] Avoid overflow at boundary

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Date:   Thu, 20 Aug 2020 16:19:23 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        rth@...ddle.net, ink@...assic.park.msu.ru, mattst88@...il.com,
        tony.luck@...el.com, fenghua.yu@...el.com, schnelle@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, borntraeger@...ibm.com, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, James.Bottomley@...senPartnership.com, deller@....de
Cc:     sfr@...b.auug.org.au, hch@....de, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-s390@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: [RFT][PATCH 0/7] Avoid overflow at boundary_size

We are expending the default DMA segmentation boundary to its
possible maximum value (ULONG_MAX) to indicate that a device
doesn't specify a boundary limit. So all dma_get_seg_boundary
callers should take a precaution with the return values since
it would easily get overflowed.

I scanned the entire kernel tree for all the existing callers
and found that most of callers may get overflowed in two ways:
either "+ 1" or passing it to ALIGN() that does "+ mask".

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 this series of patches fix the potential overflow with this
overflow-free shortcut.

As I don't think that I have these platforms, marking RFT.

Thanks
Nic

Nicolin Chen (7):
  powerpc/iommu: Avoid overflow at boundary_size
  alpha: Avoid overflow at boundary_size
  ia64/sba_iommu: Avoid overflow at boundary_size
  s390/pci_dma: Avoid overflow at boundary_size
  sparc: Avoid overflow at boundary_size
  x86/amd_gart: Avoid overflow at boundary_size
  parisc: Avoid overflow at boundary_size

 arch/alpha/kernel/pci_iommu.c    | 10 ++++------
 arch/ia64/hp/common/sba_iommu.c  |  4 ++--
 arch/powerpc/kernel/iommu.c      | 11 +++++------
 arch/s390/pci/pci_dma.c          |  4 ++--
 arch/sparc/kernel/iommu-common.c |  9 +++------
 arch/sparc/kernel/iommu.c        |  4 ++--
 arch/sparc/kernel/pci_sun4v.c    |  4 ++--
 arch/x86/kernel/amd_gart_64.c    |  4 ++--
 drivers/parisc/ccio-dma.c        |  4 ++--
 drivers/parisc/sba_iommu.c       |  4 ++--
 10 files changed, 26 insertions(+), 32 deletions(-)

-- 
2.17.1