On 8/21/20 1:19 AM, Nicolin Chen wrote:
> 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.
Hi Nicolin,
haven't seen any other feedback from other maintainers,
so I guess you will resend this?
On first glance it seems to make sense.
I'm a little confused why it is only a "potential overflow"
while this part
"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"
sounds to me like ULONG_MAX is actually used, does that
mean there are currently no devices which do not specify a
boundary limit?
>
> 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(-)
>
