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