Revision ec3937107ab43f3e8b2bc9dad95710043c462ff7 authored by Baoquan He on 04 April 2019, 02:03:13 UTC, committed by Borislav Petkov on 18 April 2019, 08:42:58 UTC
kernel_randomize_memory() uses __PHYSICAL_MASK_SHIFT to calculate the maximum amount of system RAM supported. The size of the direct mapping section is obtained from the smaller one of the below two values: (actual system RAM size + padding size) vs (max system RAM size supported) This calculation is wrong since commit b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52"). In it, __PHYSICAL_MASK_SHIFT was changed to be 52, regardless of whether the kernel is using 4-level or 5-level page tables. Thus, it will always use 4 PB as the maximum amount of system RAM, even in 4-level paging mode where it should actually be 64 TB. Thus, the size of the direct mapping section will always be the sum of the actual system RAM size plus the padding size. Even when the amount of system RAM is 64 TB, the following layout will still be used. Obviously KALSR will be weakened significantly. |____|_______actual RAM_______|_padding_|______the rest_______| 0 64TB ~120TB Instead, it should be like this: |____|_______actual RAM_______|_________the rest______________| 0 64TB ~120TB The size of padding region is controlled by CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING, which is 10 TB by default. The above issue only exists when CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING is set to a non-zero value, which is the case when CONFIG_MEMORY_HOTPLUG is enabled. Otherwise, using __PHYSICAL_MASK_SHIFT doesn't affect KASLR. Fix it by replacing __PHYSICAL_MASK_SHIFT with MAX_PHYSMEM_BITS. [ bp: Massage commit message. ] Fixes: b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52") Signed-off-by: Baoquan He <bhe@redhat.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Thomas Garnier <thgarnie@google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: frank.ramsay@hpe.com Cc: herbert@gondor.apana.org.au Cc: kirill@shutemov.name Cc: mike.travis@hpe.com Cc: thgarnie@google.com Cc: x86-ml <x86@kernel.org> Cc: yamada.masahiro@socionext.com Link: https://lkml.kernel.org/r/20190417083536.GE7065@MiWiFi-R3L-srv
1 parent a943245
memfd.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 <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 void memfd_tag_pins(struct xa_state *xas)
{
struct page *page;
unsigned int tagged = 0;
lru_add_drain();
xas_lock_irq(xas);
xas_for_each(xas, page, ULONG_MAX) {
if (xa_is_value(page))
continue;
if (page_count(page) - page_mapcount(page) > 1)
xas_set_mark(xas, MEMFD_TAG_PINNED);
if (++tagged % XA_CHECK_SCHED)
continue;
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++) {
unsigned int tagged = 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, page, ULONG_MAX, MEMFD_TAG_PINNED) {
bool clear = true;
if (xa_is_value(page))
continue;
if (page_count(page) - page_mapcount(page) != 1) {
/*
* 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);
if (++tagged % XA_CHECK_SCHED)
continue;
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_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
*
* 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;
}
}
*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 long arg)
{
long error;
switch (cmd) {
case F_ADD_SEALS:
/* disallow upper 32bit */
if (arg > UINT_MAX)
return -EINVAL;
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)
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;
}
/* 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) {
struct user_struct *user = NULL;
file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user,
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_ALLOW_SEALING) {
file_seals = memfd_file_seals_ptr(file);
*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;
}
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...