Re: [PATCH v5 13/15] resource: Move devmem revoke code to resource framework

John Hubbard
2020-10-31T06:36:47Z

On 10/30/20 3:08 AM, Daniel Vetter 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.

This seems like it's doing a lot more than just code movement, right?
Should we list some of that here?

Also, I'm seeing a crash due to this commit. More below:

>
> 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.ch>
> --
> v3:
> - add barrier for consistency and document why we don't have to check
> for NULL (Jason)
> v4
> - Adjust comments to reflect the general nature of this iomem revoke
> code now (Dan)
> ---
> 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 7dcf9e4ea79d..43c871dc7477 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>
> @@ -836,42 +833,6 @@ 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;
> @@ -891,7 +852,7 @@ 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();

The problem is that iomem_get_mapping() returns NULL for the !CONFIG_IO_STRICT_DEVMEM
case. And then we have pre-existing fs code that expects to go "up and over", like this:

static int do_dentry_open(struct file *f,
struct inode *inode,
int (*open)(struct inode *, struct file *))
{
...

file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);

...and it crashes on that line fairly early in bootup.

Not sure what to suggest for this patch, but wanted to get this report out at least.

thanks,
--
John Hubbard
NVIDIA

>
> return 0;
> }
> @@ -1023,48 +984,6 @@ 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;
> @@ -1086,8 +1005,6 @@ 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 5135d4b86cd6..02a5466245c0 100644
> --- a/include/linux/ioport.h
> +++ b/include/linux/ioport.h
> @@ -307,11 +307,7 @@ 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 3ae2f56cc79d..5ecc3187fe2d 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>
>
>
> @@ -1115,6 +1118,58 @@ 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 iomem_get_mapping users
> + * 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);
> +}
> +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
> @@ -1182,7 +1237,7 @@ 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;
> }
> @@ -1782,4 +1837,48 @@ 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 iomem revocation inode initialized.
> + * Pairs with smp_load_acquire() in revoke_iomem().
> + */
> + smp_store_release(&iomem_inode, inode);
> +
> + return 0;
> +}
> +
> +fs_initcall(iomem_init_inode);
> +
> __setup("iomem=", strict_iomem);
>