From ace9429bb58fd418f0c81d4c2835699bddf6bde6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Thu, 11 Apr 2024 10:27:49 +0200 Subject: Adding upstream version 6.6.15. Signed-off-by: Daniel Baumann --- mm/memfd.c | 396 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 396 insertions(+) create mode 100644 mm/memfd.c (limited to 'mm/memfd.c') diff --git a/mm/memfd.c b/mm/memfd.c new file mode 100644 index 000000000..2dba2cb6f --- /dev/null +++ b/mm/memfd.c @@ -0,0 +1,396 @@ +/* + * 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 +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* + * 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 void memfd_tag_pins(struct xa_state *xas) +{ + struct page *page; + int latency = 0; + int cache_count; + + lru_add_drain(); + + xas_lock_irq(xas); + xas_for_each(xas, page, ULONG_MAX) { + cache_count = 1; + if (!xa_is_value(page) && + PageTransHuge(page) && !PageHuge(page)) + cache_count = HPAGE_PMD_NR; + + if (!xa_is_value(page) && + page_count(page) - total_mapcount(page) != cache_count) + xas_set_mark(xas, MEMFD_TAG_PINNED); + if (cache_count != 1) + xas_set(xas, page->index + cache_count); + + latency += cache_count; + 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); +} + +/* + * 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 pages + * 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 pages to avoid races. + */ +static int memfd_wait_for_pins(struct address_space *mapping) +{ + XA_STATE(xas, &mapping->i_pages, 0); + struct page *page; + int error, scan; + + memfd_tag_pins(&xas); + + error = 0; + for (scan = 0; scan <= LAST_SCAN; scan++) { + int latency = 0; + int cache_count; + + 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, page, ULONG_MAX, MEMFD_TAG_PINNED) { + bool clear = true; + + cache_count = 1; + if (!xa_is_value(page) && + PageTransHuge(page) && !PageHuge(page)) + cache_count = HPAGE_PMD_NR; + + if (!xa_is_value(page) && cache_count != + page_count(page) - total_mapcount(page)) { + /* + * On the last scan, we clean up all those tags + * we inserted; but make a note that we still + * found pages pinned. + */ + if (scan == LAST_SCAN) + error = -EBUSY; + else + clear = false; + } + if (clear) + xas_clear_mark(&xas, MEMFD_TAG_PINNED); + + latency += cache_count; + 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; + + if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) { + pr_warn_once( + "%s[%d]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set\n", + current->comm, task_pid_nr(current)); + } + + 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; +} -- cgit v1.2.3