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855d44434f
Quoting Dmitry:
"refcount_inc() needs to be done before fd_install(). After
fd_install() finishes, the fd can be used by userspace and
we can have secret data in memory before the refcount_inc().
A straightforward misuse where a user will predict the returned
fd in another thread before the syscall returns and will use it
to store secret data is somewhat dubious because such a user just
shoots themself in the foot.
But a more interesting misuse would be to close the predicted fd
and decrement the refcount before the corresponding refcount_inc,
this way one can briefly drop the refcount to zero while there are
other users of secretmem."
Move fd_install() after refcount_inc().
Link: https://lkml.kernel.org/r/20211021154046.880251-1-keescook@chromium.org
Link: https://lore.kernel.org/lkml/CACT4Y+b1sW6-Hkn8HQYw_SsT7X3tp-CJNh2ci0wG3ZnQz9jjig@mail.gmail.com
Fixes: 9a436f8ff6
("PM: hibernate: disable when there are active secretmem users")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jordy Zomer <jordy@pwning.systems>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
258 lines
5.5 KiB
C
258 lines
5.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright IBM Corporation, 2021
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*
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* Author: Mike Rapoport <rppt@linux.ibm.com>
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*/
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#include <linux/mm.h>
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#include <linux/fs.h>
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#include <linux/swap.h>
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#include <linux/mount.h>
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#include <linux/memfd.h>
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#include <linux/bitops.h>
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#include <linux/printk.h>
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#include <linux/pagemap.h>
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#include <linux/syscalls.h>
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#include <linux/pseudo_fs.h>
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#include <linux/secretmem.h>
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#include <linux/set_memory.h>
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#include <linux/sched/signal.h>
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#include <uapi/linux/magic.h>
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#include <asm/tlbflush.h>
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#include "internal.h"
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#undef pr_fmt
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#define pr_fmt(fmt) "secretmem: " fmt
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/*
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* Define mode and flag masks to allow validation of the system call
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* parameters.
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*/
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#define SECRETMEM_MODE_MASK (0x0)
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#define SECRETMEM_FLAGS_MASK SECRETMEM_MODE_MASK
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static bool secretmem_enable __ro_after_init;
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module_param_named(enable, secretmem_enable, bool, 0400);
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MODULE_PARM_DESC(secretmem_enable,
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"Enable secretmem and memfd_secret(2) system call");
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static atomic_t secretmem_users;
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bool secretmem_active(void)
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{
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return !!atomic_read(&secretmem_users);
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}
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static vm_fault_t secretmem_fault(struct vm_fault *vmf)
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{
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struct address_space *mapping = vmf->vma->vm_file->f_mapping;
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struct inode *inode = file_inode(vmf->vma->vm_file);
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pgoff_t offset = vmf->pgoff;
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gfp_t gfp = vmf->gfp_mask;
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unsigned long addr;
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struct page *page;
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int err;
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if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
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return vmf_error(-EINVAL);
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retry:
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page = find_lock_page(mapping, offset);
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if (!page) {
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page = alloc_page(gfp | __GFP_ZERO);
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if (!page)
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return VM_FAULT_OOM;
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err = set_direct_map_invalid_noflush(page);
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if (err) {
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put_page(page);
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return vmf_error(err);
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}
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__SetPageUptodate(page);
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err = add_to_page_cache_lru(page, mapping, offset, gfp);
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if (unlikely(err)) {
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put_page(page);
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/*
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* If a split of large page was required, it
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* already happened when we marked the page invalid
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* which guarantees that this call won't fail
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*/
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set_direct_map_default_noflush(page);
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if (err == -EEXIST)
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goto retry;
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return vmf_error(err);
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}
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addr = (unsigned long)page_address(page);
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flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
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}
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vmf->page = page;
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return VM_FAULT_LOCKED;
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}
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static const struct vm_operations_struct secretmem_vm_ops = {
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.fault = secretmem_fault,
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};
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static int secretmem_release(struct inode *inode, struct file *file)
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{
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atomic_dec(&secretmem_users);
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return 0;
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}
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static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
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{
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unsigned long len = vma->vm_end - vma->vm_start;
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if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
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return -EINVAL;
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if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
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return -EAGAIN;
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vma->vm_flags |= VM_LOCKED | VM_DONTDUMP;
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vma->vm_ops = &secretmem_vm_ops;
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return 0;
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}
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bool vma_is_secretmem(struct vm_area_struct *vma)
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{
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return vma->vm_ops == &secretmem_vm_ops;
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}
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static const struct file_operations secretmem_fops = {
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.release = secretmem_release,
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.mmap = secretmem_mmap,
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};
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static bool secretmem_isolate_page(struct page *page, isolate_mode_t mode)
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{
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return false;
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}
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static int secretmem_migratepage(struct address_space *mapping,
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struct page *newpage, struct page *page,
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enum migrate_mode mode)
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{
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return -EBUSY;
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}
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static void secretmem_freepage(struct page *page)
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{
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set_direct_map_default_noflush(page);
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clear_highpage(page);
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}
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const struct address_space_operations secretmem_aops = {
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.set_page_dirty = __set_page_dirty_no_writeback,
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.freepage = secretmem_freepage,
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.migratepage = secretmem_migratepage,
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.isolate_page = secretmem_isolate_page,
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};
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static struct vfsmount *secretmem_mnt;
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static struct file *secretmem_file_create(unsigned long flags)
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{
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struct file *file = ERR_PTR(-ENOMEM);
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struct inode *inode;
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inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
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if (IS_ERR(inode))
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return ERR_CAST(inode);
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file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
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O_RDWR, &secretmem_fops);
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if (IS_ERR(file))
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goto err_free_inode;
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mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
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mapping_set_unevictable(inode->i_mapping);
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inode->i_mapping->a_ops = &secretmem_aops;
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/* pretend we are a normal file with zero size */
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inode->i_mode |= S_IFREG;
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inode->i_size = 0;
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return file;
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err_free_inode:
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iput(inode);
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return file;
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}
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SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
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{
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struct file *file;
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int fd, err;
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/* make sure local flags do not confict with global fcntl.h */
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BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
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if (!secretmem_enable)
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return -ENOSYS;
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if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
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return -EINVAL;
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if (atomic_read(&secretmem_users) < 0)
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return -ENFILE;
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fd = get_unused_fd_flags(flags & O_CLOEXEC);
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if (fd < 0)
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return fd;
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file = secretmem_file_create(flags);
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if (IS_ERR(file)) {
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err = PTR_ERR(file);
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goto err_put_fd;
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}
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file->f_flags |= O_LARGEFILE;
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atomic_inc(&secretmem_users);
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fd_install(fd, file);
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return fd;
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err_put_fd:
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put_unused_fd(fd);
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return err;
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}
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static int secretmem_init_fs_context(struct fs_context *fc)
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{
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return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
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}
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static struct file_system_type secretmem_fs = {
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.name = "secretmem",
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.init_fs_context = secretmem_init_fs_context,
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.kill_sb = kill_anon_super,
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};
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static int secretmem_init(void)
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{
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int ret = 0;
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if (!secretmem_enable)
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return ret;
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secretmem_mnt = kern_mount(&secretmem_fs);
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if (IS_ERR(secretmem_mnt))
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ret = PTR_ERR(secretmem_mnt);
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/* prevent secretmem mappings from ever getting PROT_EXEC */
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secretmem_mnt->mnt_flags |= MNT_NOEXEC;
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return ret;
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}
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fs_initcall(secretmem_init);
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