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

From: Daniel Vetter
Date: Wed Oct 21 2020 - 15:26:06 EST

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On Wed, Oct 21, 2020 at 8:59 PM Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> On Wed, Oct 21, 2020 at 1:57 AM Daniel Vetter <daniel.vetter@xxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > Cc: Jan Kara <jack@xxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > Cc: linux-samsung-soc@xxxxxxxxxxxxxxx
> > Cc: linux-media@xxxxxxxxxxxxxxx
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > --
> > 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"

Yeah makes sense I fix up the comments, I'll do that in v4. Need to
fix up my mangeld sob line anyway :-)

Thanks for taking a careful look at this!

Cheers, Daniel

> Other than that:
>
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Next message: SeongJae Park: "Re: [PATCH v2] Documentation: kunit: Update Kconfig parts for KUNIT's module support"
Previous message: Daniel Vetter: "Re: [PATCH v3 12/16] PCI: Obey iomem restrictions for procfs mmap"
In reply to: Dan Williams: "Re: [PATCH v3 14/16] resource: Move devmem revoke code to resource framework"
Next in thread: Daniel Vetter: "[PATCH v3 13/16] /dev/mem: Only set filp->f_mapping"
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