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-rw-r--r--mm/secretmem.c295
1 files changed, 295 insertions, 0 deletions
diff --git a/mm/secretmem.c b/mm/secretmem.c
new file mode 100644
index 0000000000..3afb5ad701
--- /dev/null
+++ b/mm/secretmem.c
@@ -0,0 +1,295 @@
+// 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 = 1;
+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;
+ struct folio *folio;
+ 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) {
+ folio = folio_alloc(gfp | __GFP_ZERO, 0);
+ if (!folio) {
+ ret = VM_FAULT_OOM;
+ goto out;
+ }
+
+ page = &folio->page;
+ err = set_direct_map_invalid_noflush(page);
+ if (err) {
+ folio_put(folio);
+ ret = vmf_error(err);
+ goto out;
+ }
+
+ __folio_mark_uptodate(folio);
+ err = filemap_add_folio(mapping, folio, offset, gfp);
+ if (unlikely(err)) {
+ folio_put(folio);
+ /*
+ * 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_ok(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
+ return -EAGAIN;
+
+ vm_flags_set(vma, 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 mnt_idmap *idmap,
+ 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(idmap, 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;
+ 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);