[PATCH v7 12/17] PCI: Revoke mappings like devmem

Daniel Vetter
2020-11-27T17:02:21Z

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.

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: 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
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
--
v2:
- Totally new approach: Adjust filp->f_mapping at open time. Note that
this now works on all architectures, not just those support
ARCH_GENERIC_PCI_MMAP_RESOURCE
---
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 d15c881e2e7e..3f1c31bc0b7c 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -929,6 +929,7 @@ 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)
@@ -941,6 +942,7 @@ 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)
@@ -1156,6 +1158,8 @@ 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();
res_attr->attr.name = res_attr_name;
res_attr->attr.mode = 0600;
res_attr->size = pci_resource_len(pdev, num);
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;
}