Re: [PATCH v3 14/16] resource: Move devmem revoke code to resource framework

[Dan Williams <dan.j.williams@intel.com>]

On Wed, Oct 21, 2020 at 1:57 AM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> We want all iomem mmaps to consistently revoke ptes when the kernel
> takes over and CONFIG_IO_STRICT_DEVMEM is enabled. This includes the
> pci bar mmaps available through procfs and sysfs, which currently do
> not revoke mappings.
>
> To prepare for this, move the code from the /dev/kmem driver to
> kernel/resource.c.
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 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: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.com>
> --
> v3:
> - add barrier for consistency and document why we don't have to check
>   for NULL (Jason)
> ---
>  drivers/char/mem.c     |  85 +---------------------------------
>  include/linux/ioport.h |   6 +--
>  kernel/resource.c      | 101 ++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 102 insertions(+), 90 deletions(-)
>
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index 5502f56f3655..53338aad8d28 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -31,9 +31,6 @@
>  #include <linux/uio.h>
>  #include <linux/uaccess.h>
>  #include <linux/security.h>
> -#include <linux/pseudo_fs.h>
> -#include <uapi/linux/magic.h>
> -#include <linux/mount.h>
>
>  #ifdef CONFIG_IA64
>  # include <linux/efi.h>
> @@ -809,42 +806,6 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
>         return ret;
>  }
>
> -static struct inode *devmem_inode;
> -
> -#ifdef CONFIG_IO_STRICT_DEVMEM
> -void revoke_devmem(struct resource *res)
> -{
> -       /* pairs with smp_store_release() in devmem_init_inode() */
> -       struct inode *inode = smp_load_acquire(&devmem_inode);
> -
> -       /*
> -        * Check that the initialization has completed. Losing the race
> -        * is ok because it means drivers are claiming resources before
> -        * the fs_initcall level of init and prevent /dev/mem from
> -        * establishing mappings.
> -        */
> -       if (!inode)
> -               return;
> -
> -       /*
> -        * The expectation is that the driver has successfully marked
> -        * the resource busy by this point, so devmem_is_allowed()
> -        * should start returning false, however for performance this
> -        * does not iterate the entire resource range.
> -        */
> -       if (devmem_is_allowed(PHYS_PFN(res->start)) &&
> -           devmem_is_allowed(PHYS_PFN(res->end))) {
> -               /*
> -                * *cringe* iomem=relaxed says "go ahead, what's the
> -                * worst that can happen?"
> -                */
> -               return;
> -       }
> -
> -       unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
> -}
> -#endif
> -
>  static int open_port(struct inode *inode, struct file *filp)
>  {
>         int rc;
> @@ -864,7 +825,7 @@ static int open_port(struct inode *inode, struct file *filp)
>          * revocations when drivers want to take over a /dev/mem mapped
>          * range.
>          */
> -       filp->f_mapping = inode->i_mapping;
> +       filp->f_mapping = iomem_get_mapping();
>
>         return 0;
>  }
> @@ -995,48 +956,6 @@ static char *mem_devnode(struct device *dev, umode_t *mode)
>
>  static struct class *mem_class;
>
> -static int devmem_fs_init_fs_context(struct fs_context *fc)
> -{
> -       return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM;
> -}
> -
> -static struct file_system_type devmem_fs_type = {
> -       .name           = "devmem",
> -       .owner          = THIS_MODULE,
> -       .init_fs_context = devmem_fs_init_fs_context,
> -       .kill_sb        = kill_anon_super,
> -};
> -
> -static int devmem_init_inode(void)
> -{
> -       static struct vfsmount *devmem_vfs_mount;
> -       static int devmem_fs_cnt;
> -       struct inode *inode;
> -       int rc;
> -
> -       rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt);
> -       if (rc < 0) {
> -               pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc);
> -               return rc;
> -       }
> -
> -       inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb);
> -       if (IS_ERR(inode)) {
> -               rc = PTR_ERR(inode);
> -               pr_err("Cannot allocate inode for /dev/mem: %d\n", rc);
> -               simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt);
> -               return rc;
> -       }
> -
> -       /*
> -        * Publish /dev/mem initialized.
> -        * Pairs with smp_load_acquire() in revoke_devmem().
> -        */
> -       smp_store_release(&devmem_inode, inode);
> -
> -       return 0;
> -}
> -
>  static int __init chr_dev_init(void)
>  {
>         int minor;
> @@ -1058,8 +977,6 @@ static int __init chr_dev_init(void)
>                  */
>                 if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
>                         continue;
> -               if ((minor == DEVMEM_MINOR) && devmem_init_inode() != 0)
> -                       continue;
>
>                 device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
>                               NULL, devlist[minor].name);
> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> index 6c2b06fe8beb..8ffb61b36606 100644
> --- a/include/linux/ioport.h
> +++ b/include/linux/ioport.h
> @@ -302,11 +302,7 @@ struct resource *devm_request_free_mem_region(struct device *dev,
>  struct resource *request_free_mem_region(struct resource *base,
>                 unsigned long size, const char *name);
>
> -#ifdef CONFIG_IO_STRICT_DEVMEM
> -void revoke_devmem(struct resource *res);
> -#else
> -static inline void revoke_devmem(struct resource *res) { };
> -#endif
> +extern struct address_space *iomem_get_mapping(void);
>
>  #endif /* __ASSEMBLY__ */
>  #endif /* _LINUX_IOPORT_H */
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 841737bbda9e..a92fed5b9997 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -18,12 +18,15 @@
>  #include <linux/spinlock.h>
>  #include <linux/fs.h>
>  #include <linux/proc_fs.h>
> +#include <linux/pseudo_fs.h>
>  #include <linux/sched.h>
>  #include <linux/seq_file.h>
>  #include <linux/device.h>
>  #include <linux/pfn.h>
>  #include <linux/mm.h>
> +#include <linux/mount.h>
>  #include <linux/resource_ext.h>
> +#include <uapi/linux/magic.h>
>  #include <asm/io.h>
>
>
> @@ -1112,6 +1115,58 @@ resource_size_t resource_alignment(struct resource *res)
>
>  static DECLARE_WAIT_QUEUE_HEAD(muxed_resource_wait);
>
> +static struct inode *iomem_inode;
> +
> +#ifdef CONFIG_IO_STRICT_DEVMEM
> +static void revoke_iomem(struct resource *res)
> +{
> +       /* pairs with smp_store_release() in iomem_init_inode() */
> +       struct inode *inode = smp_load_acquire(&iomem_inode);
> +
> +       /*
> +        * Check that the initialization has completed. Losing the race
> +        * is ok because it means drivers are claiming resources before
> +        * the fs_initcall level of init and prevent /dev/mem from

How about:

s,/dev/mem,iomem_get_mapping() users,

...now that this facility is generalized?

> +        * establishing mappings.
> +        */
> +       if (!inode)
> +               return;
> +
> +       /*
> +        * The expectation is that the driver has successfully marked
> +        * the resource busy by this point, so devmem_is_allowed()
> +        * should start returning false, however for performance this
> +        * does not iterate the entire resource range.
> +        */
> +       if (devmem_is_allowed(PHYS_PFN(res->start)) &&
> +           devmem_is_allowed(PHYS_PFN(res->end))) {
> +               /*
> +                * *cringe* iomem=relaxed says "go ahead, what's the
> +                * worst that can happen?"
> +                */
> +               return;
> +       }
> +
> +       unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
> +}
> +struct address_space *iomem_get_mapping(void)
> +{
> +       /*
> +        * This function is only called from file open paths, hence guaranteed
> +        * that fs_initcalls have completed and no need to check for NULL. But
> +        * since revoke_iomem can be called before the initcall we still need
> +        * the barrier to appease checkers.
> +        */
> +       return smp_load_acquire(&iomem_inode)->i_mapping;
> +}
> +#else
> +static void revoke_iomem(struct resource *res) {}
> +struct address_space *iomem_get_mapping(void)
> +{
> +       return NULL;
> +}
> +#endif
> +
>  /**
>   * __request_region - create a new busy resource region
>   * @parent: parent resource descriptor
> @@ -1179,7 +1234,7 @@ struct resource * __request_region(struct resource *parent,
>         write_unlock(&resource_lock);
>
>         if (res && orig_parent == &iomem_resource)
> -               revoke_devmem(res);
> +               revoke_iomem(res);
>
>         return res;
>  }
> @@ -1713,4 +1768,48 @@ static int __init strict_iomem(char *str)
>         return 1;
>  }
>
> +static int iomem_fs_init_fs_context(struct fs_context *fc)
> +{
> +       return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM;
> +}
> +
> +static struct file_system_type iomem_fs_type = {
> +       .name           = "iomem",
> +       .owner          = THIS_MODULE,
> +       .init_fs_context = iomem_fs_init_fs_context,
> +       .kill_sb        = kill_anon_super,
> +};
> +
> +static int __init iomem_init_inode(void)
> +{
> +       static struct vfsmount *iomem_vfs_mount;
> +       static int iomem_fs_cnt;
> +       struct inode *inode;
> +       int rc;
> +
> +       rc = simple_pin_fs(&iomem_fs_type, &iomem_vfs_mount, &iomem_fs_cnt);
> +       if (rc < 0) {
> +               pr_err("Cannot mount iomem pseudo filesystem: %d\n", rc);
> +               return rc;
> +       }
> +
> +       inode = alloc_anon_inode(iomem_vfs_mount->mnt_sb);
> +       if (IS_ERR(inode)) {
> +               rc = PTR_ERR(inode);
> +               pr_err("Cannot allocate inode for iomem: %d\n", rc);
> +               simple_release_fs(&iomem_vfs_mount, &iomem_fs_cnt);
> +               return rc;
> +       }
> +
> +       /*
> +        * Publish /dev/mem initialized.

Similar potential fixup:

"Publish iomem revocation inode initialized"

Other than that:

Reviewed-by: Dan Williams <dan.j.williams@intel.com>