linux/mm/mprotect.c
Andi Kleen 42e4089c78 x86/speculation/l1tf: Disallow non privileged high MMIO PROT_NONE mappings
For L1TF PROT_NONE mappings are protected by inverting the PFN in the page
table entry. This sets the high bits in the CPU's address space, thus
making sure to point to not point an unmapped entry to valid cached memory.

Some server system BIOSes put the MMIO mappings high up in the physical
address space. If such an high mapping was mapped to unprivileged users
they could attack low memory by setting such a mapping to PROT_NONE. This
could happen through a special device driver which is not access
protected. Normal /dev/mem is of course access protected.

To avoid this forbid PROT_NONE mappings or mprotect for high MMIO mappings.

Valid page mappings are allowed because the system is then unsafe anyways.

It's not expected that users commonly use PROT_NONE on MMIO. But to
minimize any impact this is only enforced if the mapping actually refers to
a high MMIO address (defined as the MAX_PA-1 bit being set), and also skip
the check for root.

For mmaps this is straight forward and can be handled in vm_insert_pfn and
in remap_pfn_range().

For mprotect it's a bit trickier. At the point where the actual PTEs are
accessed a lot of state has been changed and it would be difficult to undo
on an error. Since this is a uncommon case use a separate early page talk
walk pass for MMIO PROT_NONE mappings that checks for this condition
early. For non MMIO and non PROT_NONE there are no changes.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
2018-06-20 19:10:01 +02:00

637 lines
16 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* mm/mprotect.c
*
* (C) Copyright 1994 Linus Torvalds
* (C) Copyright 2002 Christoph Hellwig
*
* Address space accounting code <alan@lxorguk.ukuu.org.uk>
* (C) Copyright 2002 Red Hat Inc, All Rights Reserved
*/
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/mempolicy.h>
#include <linux/personality.h>
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/perf_event.h>
#include <linux/pkeys.h>
#include <linux/ksm.h>
#include <linux/uaccess.h>
#include <linux/mm_inline.h>
#include <asm/pgtable.h>
#include <asm/cacheflush.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include "internal.h"
static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
struct mm_struct *mm = vma->vm_mm;
pte_t *pte, oldpte;
spinlock_t *ptl;
unsigned long pages = 0;
int target_node = NUMA_NO_NODE;
/*
* Can be called with only the mmap_sem for reading by
* prot_numa so we must check the pmd isn't constantly
* changing from under us from pmd_none to pmd_trans_huge
* and/or the other way around.
*/
if (pmd_trans_unstable(pmd))
return 0;
/*
* The pmd points to a regular pte so the pmd can't change
* from under us even if the mmap_sem is only hold for
* reading.
*/
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
/* Get target node for single threaded private VMAs */
if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
atomic_read(&vma->vm_mm->mm_users) == 1)
target_node = numa_node_id();
flush_tlb_batched_pending(vma->vm_mm);
arch_enter_lazy_mmu_mode();
do {
oldpte = *pte;
if (pte_present(oldpte)) {
pte_t ptent;
bool preserve_write = prot_numa && pte_write(oldpte);
/*
* Avoid trapping faults against the zero or KSM
* pages. See similar comment in change_huge_pmd.
*/
if (prot_numa) {
struct page *page;
page = vm_normal_page(vma, addr, oldpte);
if (!page || PageKsm(page))
continue;
/* Also skip shared copy-on-write pages */
if (is_cow_mapping(vma->vm_flags) &&
page_mapcount(page) != 1)
continue;
/*
* While migration can move some dirty pages,
* it cannot move them all from MIGRATE_ASYNC
* context.
*/
if (page_is_file_cache(page) && PageDirty(page))
continue;
/* Avoid TLB flush if possible */
if (pte_protnone(oldpte))
continue;
/*
* Don't mess with PTEs if page is already on the node
* a single-threaded process is running on.
*/
if (target_node == page_to_nid(page))
continue;
}
ptent = ptep_modify_prot_start(mm, addr, pte);
ptent = pte_modify(ptent, newprot);
if (preserve_write)
ptent = pte_mk_savedwrite(ptent);
/* Avoid taking write faults for known dirty pages */
if (dirty_accountable && pte_dirty(ptent) &&
(pte_soft_dirty(ptent) ||
!(vma->vm_flags & VM_SOFTDIRTY))) {
ptent = pte_mkwrite(ptent);
}
ptep_modify_prot_commit(mm, addr, pte, ptent);
pages++;
} else if (IS_ENABLED(CONFIG_MIGRATION)) {
swp_entry_t entry = pte_to_swp_entry(oldpte);
if (is_write_migration_entry(entry)) {
pte_t newpte;
/*
* A protection check is difficult so
* just be safe and disable write
*/
make_migration_entry_read(&entry);
newpte = swp_entry_to_pte(entry);
if (pte_swp_soft_dirty(oldpte))
newpte = pte_swp_mksoft_dirty(newpte);
set_pte_at(mm, addr, pte, newpte);
pages++;
}
if (is_write_device_private_entry(entry)) {
pte_t newpte;
/*
* We do not preserve soft-dirtiness. See
* copy_one_pte() for explanation.
*/
make_device_private_entry_read(&entry);
newpte = swp_entry_to_pte(entry);
set_pte_at(mm, addr, pte, newpte);
pages++;
}
}
} while (pte++, addr += PAGE_SIZE, addr != end);
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(pte - 1, ptl);
return pages;
}
static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
pud_t *pud, unsigned long addr, unsigned long end,
pgprot_t newprot, int dirty_accountable, int prot_numa)
{
pmd_t *pmd;
struct mm_struct *mm = vma->vm_mm;
unsigned long next;
unsigned long pages = 0;
unsigned long nr_huge_updates = 0;
unsigned long mni_start = 0;
pmd = pmd_offset(pud, addr);
do {
unsigned long this_pages;
next = pmd_addr_end(addr, end);
if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
&& pmd_none_or_clear_bad(pmd))
goto next;
/* invoke the mmu notifier if the pmd is populated */
if (!mni_start) {
mni_start = addr;
mmu_notifier_invalidate_range_start(mm, mni_start, end);
}
if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE) {
__split_huge_pmd(vma, pmd, addr, false, NULL);
} else {
int nr_ptes = change_huge_pmd(vma, pmd, addr,
newprot, prot_numa);
if (nr_ptes) {
if (nr_ptes == HPAGE_PMD_NR) {
pages += HPAGE_PMD_NR;
nr_huge_updates++;
}
/* huge pmd was handled */
goto next;
}
}
/* fall through, the trans huge pmd just split */
}
this_pages = change_pte_range(vma, pmd, addr, next, newprot,
dirty_accountable, prot_numa);
pages += this_pages;
next:
cond_resched();
} while (pmd++, addr = next, addr != end);
if (mni_start)
mmu_notifier_invalidate_range_end(mm, mni_start, end);
if (nr_huge_updates)
count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
return pages;
}
static inline unsigned long change_pud_range(struct vm_area_struct *vma,
p4d_t *p4d, unsigned long addr, unsigned long end,
pgprot_t newprot, int dirty_accountable, int prot_numa)
{
pud_t *pud;
unsigned long next;
unsigned long pages = 0;
pud = pud_offset(p4d, addr);
do {
next = pud_addr_end(addr, end);
if (pud_none_or_clear_bad(pud))
continue;
pages += change_pmd_range(vma, pud, addr, next, newprot,
dirty_accountable, prot_numa);
} while (pud++, addr = next, addr != end);
return pages;
}
static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
pgd_t *pgd, unsigned long addr, unsigned long end,
pgprot_t newprot, int dirty_accountable, int prot_numa)
{
p4d_t *p4d;
unsigned long next;
unsigned long pages = 0;
p4d = p4d_offset(pgd, addr);
do {
next = p4d_addr_end(addr, end);
if (p4d_none_or_clear_bad(p4d))
continue;
pages += change_pud_range(vma, p4d, addr, next, newprot,
dirty_accountable, prot_numa);
} while (p4d++, addr = next, addr != end);
return pages;
}
static unsigned long change_protection_range(struct vm_area_struct *vma,
unsigned long addr, unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
unsigned long next;
unsigned long start = addr;
unsigned long pages = 0;
BUG_ON(addr >= end);
pgd = pgd_offset(mm, addr);
flush_cache_range(vma, addr, end);
inc_tlb_flush_pending(mm);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
continue;
pages += change_p4d_range(vma, pgd, addr, next, newprot,
dirty_accountable, prot_numa);
} while (pgd++, addr = next, addr != end);
/* Only flush the TLB if we actually modified any entries: */
if (pages)
flush_tlb_range(vma, start, end);
dec_tlb_flush_pending(mm);
return pages;
}
unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
{
unsigned long pages;
if (is_vm_hugetlb_page(vma))
pages = hugetlb_change_protection(vma, start, end, newprot);
else
pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
return pages;
}
static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
unsigned long next, struct mm_walk *walk)
{
return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
0 : -EACCES;
}
static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
unsigned long addr, unsigned long next,
struct mm_walk *walk)
{
return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
0 : -EACCES;
}
static int prot_none_test(unsigned long addr, unsigned long next,
struct mm_walk *walk)
{
return 0;
}
static int prot_none_walk(struct vm_area_struct *vma, unsigned long start,
unsigned long end, unsigned long newflags)
{
pgprot_t new_pgprot = vm_get_page_prot(newflags);
struct mm_walk prot_none_walk = {
.pte_entry = prot_none_pte_entry,
.hugetlb_entry = prot_none_hugetlb_entry,
.test_walk = prot_none_test,
.mm = current->mm,
.private = &new_pgprot,
};
return walk_page_range(start, end, &prot_none_walk);
}
int
mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
unsigned long start, unsigned long end, unsigned long newflags)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long oldflags = vma->vm_flags;
long nrpages = (end - start) >> PAGE_SHIFT;
unsigned long charged = 0;
pgoff_t pgoff;
int error;
int dirty_accountable = 0;
if (newflags == oldflags) {
*pprev = vma;
return 0;
}
/*
* Do PROT_NONE PFN permission checks here when we can still
* bail out without undoing a lot of state. This is a rather
* uncommon case, so doesn't need to be very optimized.
*/
if (arch_has_pfn_modify_check() &&
(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
(newflags & (VM_READ|VM_WRITE|VM_EXEC)) == 0) {
error = prot_none_walk(vma, start, end, newflags);
if (error)
return error;
}
/*
* If we make a private mapping writable we increase our commit;
* but (without finer accounting) cannot reduce our commit if we
* make it unwritable again. hugetlb mapping were accounted for
* even if read-only so there is no need to account for them here
*/
if (newflags & VM_WRITE) {
/* Check space limits when area turns into data. */
if (!may_expand_vm(mm, newflags, nrpages) &&
may_expand_vm(mm, oldflags, nrpages))
return -ENOMEM;
if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
VM_SHARED|VM_NORESERVE))) {
charged = nrpages;
if (security_vm_enough_memory_mm(mm, charged))
return -ENOMEM;
newflags |= VM_ACCOUNT;
}
}
/*
* First try to merge with previous and/or next vma.
*/
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*pprev = vma_merge(mm, *pprev, start, end, newflags,
vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
vma->vm_userfaultfd_ctx);
if (*pprev) {
vma = *pprev;
VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
goto success;
}
*pprev = vma;
if (start != vma->vm_start) {
error = split_vma(mm, vma, start, 1);
if (error)
goto fail;
}
if (end != vma->vm_end) {
error = split_vma(mm, vma, end, 0);
if (error)
goto fail;
}
success:
/*
* vm_flags and vm_page_prot are protected by the mmap_sem
* held in write mode.
*/
vma->vm_flags = newflags;
dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
vma_set_page_prot(vma);
change_protection(vma, start, end, vma->vm_page_prot,
dirty_accountable, 0);
/*
* Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
* fault on access.
*/
if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
(newflags & VM_WRITE)) {
populate_vma_page_range(vma, start, end, NULL);
}
vm_stat_account(mm, oldflags, -nrpages);
vm_stat_account(mm, newflags, nrpages);
perf_event_mmap(vma);
return 0;
fail:
vm_unacct_memory(charged);
return error;
}
/*
* pkey==-1 when doing a legacy mprotect()
*/
static int do_mprotect_pkey(unsigned long start, size_t len,
unsigned long prot, int pkey)
{
unsigned long nstart, end, tmp, reqprot;
struct vm_area_struct *vma, *prev;
int error = -EINVAL;
const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
(prot & PROT_READ);
prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
return -EINVAL;
if (start & ~PAGE_MASK)
return -EINVAL;
if (!len)
return 0;
len = PAGE_ALIGN(len);
end = start + len;
if (end <= start)
return -ENOMEM;
if (!arch_validate_prot(prot, start))
return -EINVAL;
reqprot = prot;
if (down_write_killable(&current->mm->mmap_sem))
return -EINTR;
/*
* If userspace did not allocate the pkey, do not let
* them use it here.
*/
error = -EINVAL;
if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
goto out;
vma = find_vma(current->mm, start);
error = -ENOMEM;
if (!vma)
goto out;
prev = vma->vm_prev;
if (unlikely(grows & PROT_GROWSDOWN)) {
if (vma->vm_start >= end)
goto out;
start = vma->vm_start;
error = -EINVAL;
if (!(vma->vm_flags & VM_GROWSDOWN))
goto out;
} else {
if (vma->vm_start > start)
goto out;
if (unlikely(grows & PROT_GROWSUP)) {
end = vma->vm_end;
error = -EINVAL;
if (!(vma->vm_flags & VM_GROWSUP))
goto out;
}
}
if (start > vma->vm_start)
prev = vma;
for (nstart = start ; ; ) {
unsigned long mask_off_old_flags;
unsigned long newflags;
int new_vma_pkey;
/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
/* Does the application expect PROT_READ to imply PROT_EXEC */
if (rier && (vma->vm_flags & VM_MAYEXEC))
prot |= PROT_EXEC;
/*
* Each mprotect() call explicitly passes r/w/x permissions.
* If a permission is not passed to mprotect(), it must be
* cleared from the VMA.
*/
mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
VM_FLAGS_CLEAR;
new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
newflags = calc_vm_prot_bits(prot, new_vma_pkey);
newflags |= (vma->vm_flags & ~mask_off_old_flags);
/* newflags >> 4 shift VM_MAY% in place of VM_% */
if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
error = -EACCES;
goto out;
}
error = security_file_mprotect(vma, reqprot, prot);
if (error)
goto out;
tmp = vma->vm_end;
if (tmp > end)
tmp = end;
error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
if (error)
goto out;
nstart = tmp;
if (nstart < prev->vm_end)
nstart = prev->vm_end;
if (nstart >= end)
goto out;
vma = prev->vm_next;
if (!vma || vma->vm_start != nstart) {
error = -ENOMEM;
goto out;
}
prot = reqprot;
}
out:
up_write(&current->mm->mmap_sem);
return error;
}
SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
unsigned long, prot)
{
return do_mprotect_pkey(start, len, prot, -1);
}
#ifdef CONFIG_ARCH_HAS_PKEYS
SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
unsigned long, prot, int, pkey)
{
return do_mprotect_pkey(start, len, prot, pkey);
}
SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
{
int pkey;
int ret;
/* No flags supported yet. */
if (flags)
return -EINVAL;
/* check for unsupported init values */
if (init_val & ~PKEY_ACCESS_MASK)
return -EINVAL;
down_write(&current->mm->mmap_sem);
pkey = mm_pkey_alloc(current->mm);
ret = -ENOSPC;
if (pkey == -1)
goto out;
ret = arch_set_user_pkey_access(current, pkey, init_val);
if (ret) {
mm_pkey_free(current->mm, pkey);
goto out;
}
ret = pkey;
out:
up_write(&current->mm->mmap_sem);
return ret;
}
SYSCALL_DEFINE1(pkey_free, int, pkey)
{
int ret;
down_write(&current->mm->mmap_sem);
ret = mm_pkey_free(current->mm, pkey);
up_write(&current->mm->mmap_sem);
/*
* We could provie warnings or errors if any VMA still
* has the pkey set here.
*/
return ret;
}
#endif /* CONFIG_ARCH_HAS_PKEYS */