[PATCH v2 15/17] sysfs: Support zapping of binary attr mmaps

[Daniel Vetter]

We want to be able to revoke pci mmaps so that the same access rules
applies as for /dev/kmem. Revoke support for devmem was added in
3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the
region").

The simplest way to achieve this is by having the same filp->f_mapping
for all mappings, so that unmap_mapping_range can find them all, no
matter through which file they've been created. Since this must be set
at open time we need sysfs support for this.

Add an optional mapping parameter bin_attr, which is only consulted
when there's also an mmap callback, since without mmap support
allowing to adjust the ->f_mapping makes no sense.

Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Kees Cook <keescook at chromium.org>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: John Hubbard <jhubbard at nvidia.com>
Cc: Jérôme Glisse <jglisse at redhat.com>
Cc: Jan Kara <jack at suse.cz>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: linux-mm at kvack.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-samsung-soc at vger.kernel.org
Cc: linux-media at vger.kernel.org
Cc: Bjorn Helgaas <bhelgaas at google.com>
Cc: linux-pci at vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael at kernel.org>
Cc: Christian Brauner <christian.brauner at ubuntu.com>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Sourabh Jain <sourabhjain at linux.ibm.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Mauro Carvalho Chehab <mchehab+huawei at kernel.org>
Cc: Nayna Jain <nayna at linux.ibm.com>
---
 fs/sysfs/file.c       | 11 +++++++++++
 include/linux/sysfs.h |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index eb6897ab78e7..9d8ccdb000e3 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -169,6 +169,16 @@ static int sysfs_kf_bin_mmap(struct kernfs_open_file *of,
 	return battr->mmap(of->file, kobj, battr, vma);
 }
 
+static int sysfs_kf_bin_open(struct kernfs_open_file *of)
+{
+	struct bin_attribute *battr = of->kn->priv;
+
+	if (battr->mapping)
+		of->file->f_mapping = battr->mapping;
+
+	return 0;
+}
+
 void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr)
 {
 	struct kernfs_node *kn = kobj->sd, *tmp;
@@ -240,6 +250,7 @@ static const struct kernfs_ops sysfs_bin_kfops_mmap = {
 	.read		= sysfs_kf_bin_read,
 	.write		= sysfs_kf_bin_write,
 	.mmap		= sysfs_kf_bin_mmap,
+	.open		= sysfs_kf_bin_open,
 };
 
 int sysfs_add_file_mode_ns(struct kernfs_node *parent,
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 34e84122f635..a17a474d1601 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -164,11 +164,13 @@ __ATTRIBUTE_GROUPS(_name)
 
 struct file;
 struct vm_area_struct;
+struct address_space;
 
 struct bin_attribute {
 	struct attribute	attr;
 	size_t			size;
 	void			*private;
+	struct address_space	*mapping;
 	ssize_t (*read)(struct file *, struct kobject *, struct bin_attribute *,
 			char *, loff_t, size_t);
 	ssize_t (*write)(struct file *, struct kobject *, struct bin_attribute *,
-- 
2.28.0