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linux/mm/memfd.c
Vivek Kasireddy 89c1905d9c mm/gup: introduce memfd_pin_folios() for pinning memfd folios
For drivers that would like to longterm-pin the folios associated with a
memfd, the memfd_pin_folios() API provides an option to not only pin the
folios via FOLL_PIN but also to check and migrate them if they reside in
movable zone or CMA block.  This API currently works with memfds but it
should work with any files that belong to either shmemfs or hugetlbfs. 
Files belonging to other filesystems are rejected for now.

The folios need to be located first before pinning them via FOLL_PIN.  If
they are found in the page cache, they can be immediately pinned. 
Otherwise, they need to be allocated using the filesystem specific APIs
and then pinned.

[akpm@linux-foundation.org: improve the CONFIG_MMU=n situation, per SeongJae]
[vivek.kasireddy@intel.com: return -EINVAL if the end offset is greater than the size of memfd]
  Link: https://lkml.kernel.org/r/IA0PR11MB71850525CBC7D541CAB45DF1F8DB2@IA0PR11MB7185.namprd11.prod.outlook.com
Link: https://lkml.kernel.org/r/20240624063952.1572359-4-vivek.kasireddy@intel.com
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2)
Reviewed-by: David Hildenbrand <david@redhat.com> (v3)
Reviewed-by: Christoph Hellwig <hch@lst.de> (v6)
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Junxiao Chang <junxiao.chang@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-07-12 15:52:09 -07:00

425 lines
10 KiB
C

/*
* memfd_create system call and file sealing support
*
* Code was originally included in shmem.c, and broken out to facilitate
* use by hugetlbfs as well as tmpfs.
*
* This file is released under the GPL.
*/
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/khugepaged.h>
#include <linux/syscalls.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <linux/memfd.h>
#include <linux/pid_namespace.h>
#include <uapi/linux/memfd.h>
/*
* We need a tag: a new tag would expand every xa_node by 8 bytes,
* so reuse a tag which we firmly believe is never set or cleared on tmpfs
* or hugetlbfs because they are memory only filesystems.
*/
#define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE
#define LAST_SCAN 4 /* about 150ms max */
static bool memfd_folio_has_extra_refs(struct folio *folio)
{
return folio_ref_count(folio) - folio_mapcount(folio) !=
folio_nr_pages(folio);
}
static void memfd_tag_pins(struct xa_state *xas)
{
struct folio *folio;
int latency = 0;
lru_add_drain();
xas_lock_irq(xas);
xas_for_each(xas, folio, ULONG_MAX) {
if (!xa_is_value(folio) && memfd_folio_has_extra_refs(folio))
xas_set_mark(xas, MEMFD_TAG_PINNED);
if (++latency < XA_CHECK_SCHED)
continue;
latency = 0;
xas_pause(xas);
xas_unlock_irq(xas);
cond_resched();
xas_lock_irq(xas);
}
xas_unlock_irq(xas);
}
/*
* This is a helper function used by memfd_pin_user_pages() in GUP (gup.c).
* It is mainly called to allocate a folio in a memfd when the caller
* (memfd_pin_folios()) cannot find a folio in the page cache at a given
* index in the mapping.
*/
struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
{
#ifdef CONFIG_HUGETLB_PAGE
struct folio *folio;
gfp_t gfp_mask;
int err;
if (is_file_hugepages(memfd)) {
/*
* The folio would most likely be accessed by a DMA driver,
* therefore, we have zone memory constraints where we can
* alloc from. Also, the folio will be pinned for an indefinite
* amount of time, so it is not expected to be migrated away.
*/
gfp_mask = htlb_alloc_mask(hstate_file(memfd));
gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
folio = alloc_hugetlb_folio_nodemask(hstate_file(memfd),
numa_node_id(),
NULL,
gfp_mask,
false);
if (folio && folio_try_get(folio)) {
err = hugetlb_add_to_page_cache(folio,
memfd->f_mapping,
idx);
if (err) {
folio_put(folio);
free_huge_folio(folio);
return ERR_PTR(err);
}
return folio;
}
return ERR_PTR(-ENOMEM);
}
#endif
return shmem_read_folio(memfd->f_mapping, idx);
}
/*
* Setting SEAL_WRITE requires us to verify there's no pending writer. However,
* via get_user_pages(), drivers might have some pending I/O without any active
* user-space mappings (eg., direct-IO, AIO). Therefore, we look at all folios
* and see whether it has an elevated ref-count. If so, we tag them and wait for
* them to be dropped.
* The caller must guarantee that no new user will acquire writable references
* to those folios to avoid races.
*/
static int memfd_wait_for_pins(struct address_space *mapping)
{
XA_STATE(xas, &mapping->i_pages, 0);
struct folio *folio;
int error, scan;
memfd_tag_pins(&xas);
error = 0;
for (scan = 0; scan <= LAST_SCAN; scan++) {
int latency = 0;
if (!xas_marked(&xas, MEMFD_TAG_PINNED))
break;
if (!scan)
lru_add_drain_all();
else if (schedule_timeout_killable((HZ << scan) / 200))
scan = LAST_SCAN;
xas_set(&xas, 0);
xas_lock_irq(&xas);
xas_for_each_marked(&xas, folio, ULONG_MAX, MEMFD_TAG_PINNED) {
bool clear = true;
if (!xa_is_value(folio) &&
memfd_folio_has_extra_refs(folio)) {
/*
* On the last scan, we clean up all those tags
* we inserted; but make a note that we still
* found folios pinned.
*/
if (scan == LAST_SCAN)
error = -EBUSY;
else
clear = false;
}
if (clear)
xas_clear_mark(&xas, MEMFD_TAG_PINNED);
if (++latency < XA_CHECK_SCHED)
continue;
latency = 0;
xas_pause(&xas);
xas_unlock_irq(&xas);
cond_resched();
xas_lock_irq(&xas);
}
xas_unlock_irq(&xas);
}
return error;
}
static unsigned int *memfd_file_seals_ptr(struct file *file)
{
if (shmem_file(file))
return &SHMEM_I(file_inode(file))->seals;
#ifdef CONFIG_HUGETLBFS
if (is_file_hugepages(file))
return &HUGETLBFS_I(file_inode(file))->seals;
#endif
return NULL;
}
#define F_ALL_SEALS (F_SEAL_SEAL | \
F_SEAL_EXEC | \
F_SEAL_SHRINK | \
F_SEAL_GROW | \
F_SEAL_WRITE | \
F_SEAL_FUTURE_WRITE)
static int memfd_add_seals(struct file *file, unsigned int seals)
{
struct inode *inode = file_inode(file);
unsigned int *file_seals;
int error;
/*
* SEALING
* Sealing allows multiple parties to share a tmpfs or hugetlbfs file
* but restrict access to a specific subset of file operations. Seals
* can only be added, but never removed. This way, mutually untrusted
* parties can share common memory regions with a well-defined policy.
* A malicious peer can thus never perform unwanted operations on a
* shared object.
*
* Seals are only supported on special tmpfs or hugetlbfs files and
* always affect the whole underlying inode. Once a seal is set, it
* may prevent some kinds of access to the file. Currently, the
* following seals are defined:
* SEAL_SEAL: Prevent further seals from being set on this file
* SEAL_SHRINK: Prevent the file from shrinking
* SEAL_GROW: Prevent the file from growing
* SEAL_WRITE: Prevent write access to the file
* SEAL_EXEC: Prevent modification of the exec bits in the file mode
*
* As we don't require any trust relationship between two parties, we
* must prevent seals from being removed. Therefore, sealing a file
* only adds a given set of seals to the file, it never touches
* existing seals. Furthermore, the "setting seals"-operation can be
* sealed itself, which basically prevents any further seal from being
* added.
*
* Semantics of sealing are only defined on volatile files. Only
* anonymous tmpfs and hugetlbfs files support sealing. More
* importantly, seals are never written to disk. Therefore, there's
* no plan to support it on other file types.
*/
if (!(file->f_mode & FMODE_WRITE))
return -EPERM;
if (seals & ~(unsigned int)F_ALL_SEALS)
return -EINVAL;
inode_lock(inode);
file_seals = memfd_file_seals_ptr(file);
if (!file_seals) {
error = -EINVAL;
goto unlock;
}
if (*file_seals & F_SEAL_SEAL) {
error = -EPERM;
goto unlock;
}
if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
error = mapping_deny_writable(file->f_mapping);
if (error)
goto unlock;
error = memfd_wait_for_pins(file->f_mapping);
if (error) {
mapping_allow_writable(file->f_mapping);
goto unlock;
}
}
/*
* SEAL_EXEC implys SEAL_WRITE, making W^X from the start.
*/
if (seals & F_SEAL_EXEC && inode->i_mode & 0111)
seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE;
*file_seals |= seals;
error = 0;
unlock:
inode_unlock(inode);
return error;
}
static int memfd_get_seals(struct file *file)
{
unsigned int *seals = memfd_file_seals_ptr(file);
return seals ? *seals : -EINVAL;
}
long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg)
{
long error;
switch (cmd) {
case F_ADD_SEALS:
error = memfd_add_seals(file, arg);
break;
case F_GET_SEALS:
error = memfd_get_seals(file);
break;
default:
error = -EINVAL;
break;
}
return error;
}
#define MFD_NAME_PREFIX "memfd:"
#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | MFD_NOEXEC_SEAL | MFD_EXEC)
static int check_sysctl_memfd_noexec(unsigned int *flags)
{
#ifdef CONFIG_SYSCTL
struct pid_namespace *ns = task_active_pid_ns(current);
int sysctl = pidns_memfd_noexec_scope(ns);
if (!(*flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
if (sysctl >= MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL)
*flags |= MFD_NOEXEC_SEAL;
else
*flags |= MFD_EXEC;
}
if (!(*flags & MFD_NOEXEC_SEAL) && sysctl >= MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED) {
pr_err_ratelimited(
"%s[%d]: memfd_create() requires MFD_NOEXEC_SEAL with vm.memfd_noexec=%d\n",
current->comm, task_pid_nr(current), sysctl);
return -EACCES;
}
#endif
return 0;
}
SYSCALL_DEFINE2(memfd_create,
const char __user *, uname,
unsigned int, flags)
{
unsigned int *file_seals;
struct file *file;
int fd, error;
char *name;
long len;
if (!(flags & MFD_HUGETLB)) {
if (flags & ~(unsigned int)MFD_ALL_FLAGS)
return -EINVAL;
} else {
/* Allow huge page size encoding in flags. */
if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
return -EINVAL;
}
/* Invalid if both EXEC and NOEXEC_SEAL are set.*/
if ((flags & MFD_EXEC) && (flags & MFD_NOEXEC_SEAL))
return -EINVAL;
error = check_sysctl_memfd_noexec(&flags);
if (error < 0)
return error;
/* length includes terminating zero */
len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
if (len <= 0)
return -EFAULT;
if (len > MFD_NAME_MAX_LEN + 1)
return -EINVAL;
name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
if (!name)
return -ENOMEM;
strcpy(name, MFD_NAME_PREFIX);
if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
error = -EFAULT;
goto err_name;
}
/* terminating-zero may have changed after strnlen_user() returned */
if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
error = -EFAULT;
goto err_name;
}
fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
if (fd < 0) {
error = fd;
goto err_name;
}
if (flags & MFD_HUGETLB) {
file = hugetlb_file_setup(name, 0, VM_NORESERVE,
HUGETLB_ANONHUGE_INODE,
(flags >> MFD_HUGE_SHIFT) &
MFD_HUGE_MASK);
} else
file = shmem_file_setup(name, 0, VM_NORESERVE);
if (IS_ERR(file)) {
error = PTR_ERR(file);
goto err_fd;
}
file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
file->f_flags |= O_LARGEFILE;
if (flags & MFD_NOEXEC_SEAL) {
struct inode *inode = file_inode(file);
inode->i_mode &= ~0111;
file_seals = memfd_file_seals_ptr(file);
if (file_seals) {
*file_seals &= ~F_SEAL_SEAL;
*file_seals |= F_SEAL_EXEC;
}
} else if (flags & MFD_ALLOW_SEALING) {
/* MFD_EXEC and MFD_ALLOW_SEALING are set */
file_seals = memfd_file_seals_ptr(file);
if (file_seals)
*file_seals &= ~F_SEAL_SEAL;
}
fd_install(fd, file);
kfree(name);
return fd;
err_fd:
put_unused_fd(fd);
err_name:
kfree(name);
return error;
}