Messages in this thread |  | | Subject | Re: [PATCH v3 4/6] iommu: Move IOMMU pagesize check to attach_device | From | Lu Baolu <> | Date | Thu, 21 Oct 2021 10:22:30 +0800 |
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On 10/20/21 10:22 PM, Marc Zyngier wrote: > On Wed, 20 Oct 2021 06:21:44 +0100, > Lu Baolu <baolu.lu@linux.intel.com> wrote: >> >> On 2021/10/20 0:37, Sven Peter via iommu wrote: >>> The iova allocator is capable of handling any granularity which is a power >>> of two. Remove the much stronger condition that the granularity must be >>> smaller or equal to the CPU page size from a BUG_ON there. >>> Instead, check this condition during __iommu_attach_device and fail >>> gracefully. >>> >>> Signed-off-by: Sven Peter<sven@svenpeter.dev> >>> --- >>> drivers/iommu/iommu.c | 35 ++++++++++++++++++++++++++++++++--- >>> drivers/iommu/iova.c | 7 ++++--- >>> include/linux/iommu.h | 5 +++++ >>> 3 files changed, 41 insertions(+), 6 deletions(-) >>> >>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >>> index dd7863e453a5..28896739964b 100644 >>> --- a/drivers/iommu/iommu.c >>> +++ b/drivers/iommu/iommu.c >>> @@ -80,6 +80,8 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus, >>> unsigned type); >>> static int __iommu_attach_device(struct iommu_domain *domain, >>> struct device *dev); >>> +static void __iommu_detach_device(struct iommu_domain *domain, >>> + struct device *dev); >>> static int __iommu_attach_group(struct iommu_domain *domain, >>> struct iommu_group *group); >>> static void __iommu_detach_group(struct iommu_domain *domain, >>> @@ -1974,6 +1976,19 @@ void iommu_domain_free(struct iommu_domain *domain) >>> } >>> EXPORT_SYMBOL_GPL(iommu_domain_free); >>> +static int iommu_check_page_size(struct iommu_domain *domain) >>> +{ >>> + if (!iommu_is_paging_domain(domain)) >>> + return 0; >>> + >>> + if (!(domain->pgsize_bitmap & (PAGE_SIZE | (PAGE_SIZE - 1)))) { >>> + pr_warn("IOMMU pages cannot exactly represent CPU pages.\n"); >>> + return -EFAULT; >>> + } >>> + >>> + return 0; >>> +} >>> + >>> static int __iommu_attach_device(struct iommu_domain *domain, >>> struct device *dev) >>> { >>> @@ -1983,9 +1998,23 @@ static int __iommu_attach_device(struct iommu_domain *domain, >>> return -ENODEV; >>> ret = domain->ops->attach_dev(domain, dev); >>> - if (!ret) >>> - trace_attach_device_to_domain(dev); >>> - return ret; >>> + if (ret) >>> + return ret; >>> + >>> + /* >>> + * Check that CPU pages can be represented by the IOVA granularity. >>> + * This has to be done after ops->attach_dev since many IOMMU drivers >>> + * only limit domain->pgsize_bitmap after having attached the first >>> + * device. >>> + */ >>> + ret = iommu_check_page_size(domain); >>> + if (ret) { >>> + __iommu_detach_device(domain, dev); >>> + return ret; >>> + } >> >> It looks odd. __iommu_attach_device() attaches an I/O page table for a >> device. How does it relate to CPU pages? Why is it a failure case if CPU >> page size is not covered? > > If you allocate a CPU PAGE_SIZE'd region, and point it at a device > that now can DMA to more than what you have allocated because the > IOMMU's own page size is larger, the device has now access to data it > shouldn't see. In my book, that's a pretty bad thing.
But even you enforce the CPU page size check here, this problem still exists unless all DMA buffers are PAGE_SIZE aligned and sized, right?
Best regards, baolu
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