[+cc Krzysztof, Pali, Oliver]
On Thu, Feb 04, 2021 at 05:58:31PM +0100, Daniel Vetter wrote:
Since 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the region") /dev/kmem zaps ptes when the kernel requests exclusive acccess to an iomem region. And with CONFIG_IO_STRICT_DEVMEM, this is the default for all driver uses.
Except there's two more ways to access PCI BARs: sysfs and proc mmap support. Let's plug that hole.
IIUC, the idea is that if a driver calls request_mem_region() on a PCI BAR, we prevent access to the BAR via sysfs. I guess I'm OK with that if it's a real security improvement or something.
But the downside of this implementation is that it depends on iomem_get_mapping(), which doesn't work until after fs_initcalls, which means the sysfs files cannot be static attributes of devices added before that. PCI devices are typically enumerated in subsys_initcall.
Krzysztof is converting PCI sysfs files (config, rom, reset, vpd, etc) to static attributes. This is a major improvement that could get rid of pci_create_sysfs_dev_files(), the late_initcall pci_sysfs_init(), and the "sysfs_initialized" hack. This would fix a race reported by Pali [1] (thanks to Oliver for the idea [2]).
EXCEPT that this revoke change means the "resource%d", "legacy_io", and "legacy_mem" files cannot be static attributes because of iomem_get_mapping().
Any ideas on how to deal with this? Having to keep the pci_sysfs_init() initcall just for these few files seems like the tail wagging the dog.
[1] https://lore.kernel.org/r/20200716110423.xtfyb3n6tn5ixedh@pali [2] https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704ZEwLKGXQzBfqa...
For revoke_devmem() to work we need to link our vma into the same address_space, with consistent vma->vm_pgoff. ->pgoff is already adjusted, because that's how (io_)remap_pfn_range works, but for the mapping we need to adjust vma->vm_file->f_mapping. The cleanest way is to adjust this at at ->open time:
- for sysfs this is easy, now that binary attributes support this. We just set bin_attr->mapping when mmap is supported
- for procfs it's a bit more tricky, since procfs pci access has only one file per device, and access to a specific resources first needs to be set up with some ioctl calls. But mmap is only supported for the same resources as sysfs exposes with mmap support, and otherwise rejected, so we can set the mapping unconditionally at open time without harm.
A special consideration is for arch_can_pci_mmap_io() - we need to make sure that the ->f_mapping doesn't alias between ioport and iomem space. There's only 2 ways in-tree to support mmap of ioports: generic pci mmap (ARCH_GENERIC_PCI_MMAP_RESOURCE), and sparc as the single architecture hand-rolling. Both approach support ioport mmap through a special pfn range and not through magic pte attributes. Aliasing is therefore not a problem.
The only difference in access checks left is that sysfs PCI mmap does not check for CAP_RAWIO. I'm not really sure whether that should be added or not.
Acked-by: Bjorn Helgaas bhelgaas@google.com Reviewed-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Stephen Rothwell sfr@canb.auug.org.au Cc: Jason Gunthorpe jgg@ziepe.ca Cc: Kees Cook keescook@chromium.org Cc: Dan Williams dan.j.williams@intel.com Cc: Andrew Morton akpm@linux-foundation.org Cc: John Hubbard jhubbard@nvidia.com Cc: Jérôme Glisse jglisse@redhat.com Cc: Jan Kara jack@suse.cz Cc: Dan Williams dan.j.williams@intel.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: linux-mm@kvack.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-samsung-soc@vger.kernel.org Cc: linux-media@vger.kernel.org Cc: Bjorn Helgaas bhelgaas@google.com Cc: linux-pci@vger.kernel.org
drivers/pci/pci-sysfs.c | 4 ++++ drivers/pci/proc.c | 1 + 2 files changed, 5 insertions(+)
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c index 0c45b4f7b214..f8afd54ca3e1 100644 --- a/drivers/pci/pci-sysfs.c +++ b/drivers/pci/pci-sysfs.c @@ -942,6 +942,7 @@ void pci_create_legacy_files(struct pci_bus *b) b->legacy_io->read = pci_read_legacy_io; b->legacy_io->write = pci_write_legacy_io; b->legacy_io->mmap = pci_mmap_legacy_io;
- b->legacy_io->mapping = iomem_get_mapping(); pci_adjust_legacy_attr(b, pci_mmap_io); error = device_create_bin_file(&b->dev, b->legacy_io); if (error)
@@ -954,6 +955,7 @@ void pci_create_legacy_files(struct pci_bus *b) b->legacy_mem->size = 1024*1024; b->legacy_mem->attr.mode = 0600; b->legacy_mem->mmap = pci_mmap_legacy_mem;
- b->legacy_io->mapping = iomem_get_mapping(); pci_adjust_legacy_attr(b, pci_mmap_mem); error = device_create_bin_file(&b->dev, b->legacy_mem); if (error)
@@ -1169,6 +1171,8 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine) res_attr->mmap = pci_mmap_resource_uc; } }
- if (res_attr->mmap)
res_attr->mapping = iomem_get_mapping();diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c index 3a2f90beb4cb..9bab07302bbf 100644 --- a/drivers/pci/proc.c +++ b/drivers/pci/proc.c @@ -298,6 +298,7 @@ static int proc_bus_pci_open(struct inode *inode, struct file *file) fpriv->write_combine = 0;
file->private_data = fpriv;
file->f_mapping = iomem_get_mapping();
return 0;
}
2.30.0
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