diff options
Diffstat (limited to 'mm/secretmem.c')
| -rw-r--r-- | mm/secretmem.c | 293 |
1 files changed, 293 insertions, 0 deletions
diff --git a/mm/secretmem.c b/mm/secretmem.c new file mode 100644 index 000000000..04c3ac944 --- /dev/null +++ b/mm/secretmem.c @@ -0,0 +1,293 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright IBM Corporation, 2021 + * + * Author: Mike Rapoport <rppt@linux.ibm.com> + */ + +#include <linux/mm.h> +#include <linux/fs.h> +#include <linux/swap.h> +#include <linux/mount.h> +#include <linux/memfd.h> +#include <linux/bitops.h> +#include <linux/printk.h> +#include <linux/pagemap.h> +#include <linux/syscalls.h> +#include <linux/pseudo_fs.h> +#include <linux/secretmem.h> +#include <linux/set_memory.h> +#include <linux/sched/signal.h> + +#include <uapi/linux/magic.h> + +#include <asm/tlbflush.h> + +#include "internal.h" + +#undef pr_fmt +#define pr_fmt(fmt) "secretmem: " fmt + +/* + * Define mode and flag masks to allow validation of the system call + * parameters. + */ +#define SECRETMEM_MODE_MASK (0x0) +#define SECRETMEM_FLAGS_MASK SECRETMEM_MODE_MASK + +static bool secretmem_enable __ro_after_init; +module_param_named(enable, secretmem_enable, bool, 0400); +MODULE_PARM_DESC(secretmem_enable, + "Enable secretmem and memfd_secret(2) system call"); + +static atomic_t secretmem_users; + +bool secretmem_active(void) +{ + return !!atomic_read(&secretmem_users); +} + +static vm_fault_t secretmem_fault(struct vm_fault *vmf) +{ + struct address_space *mapping = vmf->vma->vm_file->f_mapping; + struct inode *inode = file_inode(vmf->vma->vm_file); + pgoff_t offset = vmf->pgoff; + gfp_t gfp = vmf->gfp_mask; + unsigned long addr; + struct page *page; + vm_fault_t ret; + int err; + + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) + return vmf_error(-EINVAL); + + filemap_invalidate_lock_shared(mapping); + +retry: + page = find_lock_page(mapping, offset); + if (!page) { + page = alloc_page(gfp | __GFP_ZERO); + if (!page) { + ret = VM_FAULT_OOM; + goto out; + } + + err = set_direct_map_invalid_noflush(page); + if (err) { + put_page(page); + ret = vmf_error(err); + goto out; + } + + __SetPageUptodate(page); + err = add_to_page_cache_lru(page, mapping, offset, gfp); + if (unlikely(err)) { + put_page(page); + /* + * If a split of large page was required, it + * already happened when we marked the page invalid + * which guarantees that this call won't fail + */ + set_direct_map_default_noflush(page); + if (err == -EEXIST) + goto retry; + + ret = vmf_error(err); + goto out; + } + + addr = (unsigned long)page_address(page); + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); + } + + vmf->page = page; + ret = VM_FAULT_LOCKED; + +out: + filemap_invalidate_unlock_shared(mapping); + return ret; +} + +static const struct vm_operations_struct secretmem_vm_ops = { + .fault = secretmem_fault, +}; + +static int secretmem_release(struct inode *inode, struct file *file) +{ + atomic_dec(&secretmem_users); + return 0; +} + +static int secretmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + unsigned long len = vma->vm_end - vma->vm_start; + + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0) + return -EINVAL; + + if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len)) + return -EAGAIN; + + vma->vm_flags |= VM_LOCKED | VM_DONTDUMP; + vma->vm_ops = &secretmem_vm_ops; + + return 0; +} + +bool vma_is_secretmem(struct vm_area_struct *vma) +{ + return vma->vm_ops == &secretmem_vm_ops; +} + +static const struct file_operations secretmem_fops = { + .release = secretmem_release, + .mmap = secretmem_mmap, +}; + +static int secretmem_migrate_folio(struct address_space *mapping, + struct folio *dst, struct folio *src, enum migrate_mode mode) +{ + return -EBUSY; +} + +static void secretmem_free_folio(struct folio *folio) +{ + set_direct_map_default_noflush(&folio->page); + folio_zero_segment(folio, 0, folio_size(folio)); +} + +const struct address_space_operations secretmem_aops = { + .dirty_folio = noop_dirty_folio, + .free_folio = secretmem_free_folio, + .migrate_folio = secretmem_migrate_folio, +}; + +static int secretmem_setattr(struct user_namespace *mnt_userns, + struct dentry *dentry, struct iattr *iattr) +{ + struct inode *inode = d_inode(dentry); + struct address_space *mapping = inode->i_mapping; + unsigned int ia_valid = iattr->ia_valid; + int ret; + + filemap_invalidate_lock(mapping); + + if ((ia_valid & ATTR_SIZE) && inode->i_size) + ret = -EINVAL; + else + ret = simple_setattr(mnt_userns, dentry, iattr); + + filemap_invalidate_unlock(mapping); + + return ret; +} + +static const struct inode_operations secretmem_iops = { + .setattr = secretmem_setattr, +}; + +static struct vfsmount *secretmem_mnt; + +static struct file *secretmem_file_create(unsigned long flags) +{ + struct file *file = ERR_PTR(-ENOMEM); + struct inode *inode; + const char *anon_name = "[secretmem]"; + const struct qstr qname = QSTR_INIT(anon_name, strlen(anon_name)); + int err; + + inode = alloc_anon_inode(secretmem_mnt->mnt_sb); + if (IS_ERR(inode)) + return ERR_CAST(inode); + + err = security_inode_init_security_anon(inode, &qname, NULL); + if (err) { + file = ERR_PTR(err); + goto err_free_inode; + } + + file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem", + O_RDWR, &secretmem_fops); + if (IS_ERR(file)) + goto err_free_inode; + + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); + mapping_set_unevictable(inode->i_mapping); + + inode->i_op = &secretmem_iops; + inode->i_mapping->a_ops = &secretmem_aops; + + /* pretend we are a normal file with zero size */ + inode->i_mode |= S_IFREG; + inode->i_size = 0; + + return file; + +err_free_inode: + iput(inode); + return file; +} + +SYSCALL_DEFINE1(memfd_secret, unsigned int, flags) +{ + struct file *file; + int fd, err; + + /* make sure local flags do not confict with global fcntl.h */ + BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC); + + if (!secretmem_enable) + return -ENOSYS; + + if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC)) + return -EINVAL; + if (atomic_read(&secretmem_users) < 0) + return -ENFILE; + + fd = get_unused_fd_flags(flags & O_CLOEXEC); + if (fd < 0) + return fd; + + file = secretmem_file_create(flags); + if (IS_ERR(file)) { + err = PTR_ERR(file); + goto err_put_fd; + } + + file->f_flags |= O_LARGEFILE; + + atomic_inc(&secretmem_users); + fd_install(fd, file); + return fd; + +err_put_fd: + put_unused_fd(fd); + return err; +} + +static int secretmem_init_fs_context(struct fs_context *fc) +{ + return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM; +} + +static struct file_system_type secretmem_fs = { + .name = "secretmem", + .init_fs_context = secretmem_init_fs_context, + .kill_sb = kill_anon_super, +}; + +static int __init secretmem_init(void) +{ + if (!secretmem_enable) + return 0; + + secretmem_mnt = kern_mount(&secretmem_fs); + if (IS_ERR(secretmem_mnt)) + return PTR_ERR(secretmem_mnt); + + /* prevent secretmem mappings from ever getting PROT_EXEC */ + secretmem_mnt->mnt_flags |= MNT_NOEXEC; + + return 0; +} +fs_initcall(secretmem_init); |