[PATCH 10/13] PCI: revoke mappings like devmem

Daniel Vetter
2020-10-07T16:45:41Z

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. Usually that's done
at ->open time, but that's a bit tricky here with all the entry points
and arch code. So instead create a fake file and adjust vma->vm_file.

Note this only works for ARCH_GENERIC_PCI_MMAP_RESOURCE. But that
seems to be a subset of architectures support STRICT_DEVMEM, so we
should be good.

The only difference in access checks left is that sysfs pci mmap does
not check for CAP_RAWIO. But I think that makes some sense compared to
/dev/mem and proc, where one file gives you access to everything and
no ownership applies.

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: 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/char/mem.c | 16 +++++++++++++++-
drivers/pci/mmap.c | 3 +++
include/linux/ioport.h | 2 ++
3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index abd4ffdc8cde..5e58a326d4ee 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -810,6 +810,7 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
}

static struct inode *devmem_inode;
+static struct vfsmount *devmem_vfs_mount;

#ifdef CONFIG_IO_STRICT_DEVMEM
void revoke_devmem(struct resource *res)
@@ -843,6 +844,20 @@ void revoke_devmem(struct resource *res)

unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
}
+
+struct file *devmem_getfile(void)
+{
+ struct file *file;
+
+ file = alloc_file_pseudo(devmem_inode, devmem_vfs_mount, "devmem",
+ O_RDWR, &kmem_fops);
+ if (IS_ERR(file))
+ return NULL;
+
+ file->f_mapping = devmem_indoe->i_mapping;
+
+ return file;
+}
#endif

static int open_port(struct inode *inode, struct file *filp)
@@ -1010,7 +1025,6 @@ static struct file_system_type devmem_fs_type = {

static int devmem_init_inode(void)
{
- static struct vfsmount *devmem_vfs_mount;
static int devmem_fs_cnt;
struct inode *inode;
int rc;
diff --git a/drivers/pci/mmap.c b/drivers/pci/mmap.c
index b8c9011987f4..63786cc9c746 100644
--- a/drivers/pci/mmap.c
+++ b/drivers/pci/mmap.c
@@ -7,6 +7,7 @@
* Author: David Woodhouse <dwmw2@infradead.org>
*/

+#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/pci.h>
@@ -64,6 +65,8 @@ int pci_mmap_resource_range(struct pci_dev *pdev, int bar,
vma->vm_pgoff += (pci_resource_start(pdev, bar) >> PAGE_SHIFT);

vma->vm_ops = &pci_phys_vm_ops;
+ fput(vma->vm_file);
+ vma->vm_file = devmem_getfile();

return io_remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
vma->vm_end - vma->vm_start,
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 6c2b06fe8beb..83238cba19fe 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -304,8 +304,10 @@ struct resource *request_free_mem_region(struct resource *base,

#ifdef CONFIG_IO_STRICT_DEVMEM
void revoke_devmem(struct resource *res);
+struct file *devm_getfile(void);
#else
static inline void revoke_devmem(struct resource *res) { };
+static inline struct file *devmem_getfile(void) { return NULL; };
#endif

#endif /* __ASSEMBLY__ */
--
2.28.0