Sasha Levin has reported KASAN out-of-bounds bug[1].
It points to "if (!is_swap_pte(pte[i]))" in unfreeze_page_vma() as a
problematic access.
The cause is that split_huge_page() doesn't handle THP correctly if it's
not allingned to PMD boundary. It can happen after mremap().
Test-case (not always triggers the bug):
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#define MB (1024UL*1024)
#define SIZE (2*MB)
#define BASE ((void *)0x400000000000)
int main()
{
char *p;
p = mmap(BASE, SIZE, PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE,
-1, 0);
if (p == MAP_FAILED)
perror("mmap"), exit(1);
p = mremap(BASE, SIZE, SIZE, MREMAP_FIXED | MREMAP_MAYMOVE,
BASE + SIZE + 8192);
if (p == MAP_FAILED)
perror("mremap"), exit(1);
system("echo 1 > /sys/kernel/debug/split_huge_pages");
return 0;
}
The patch fixes freeze and unfreeze paths to handle page table boundary
crossing.
It also makes mapcount vs. count check in split_huge_page_to_list()
stricter:
- after freeze we don't expect any subpage mapped as we remove them
from rmap when setting up migration entries;
- count must be 1, meaning only caller has reference to the page;
[1] https://gist.github.com/sashalevin/c67fbea55e7c0576972a
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 72 +++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 51 insertions(+), 21 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 22385253cd5e..ea1baf9b45b4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3115,6 +3115,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
static void freeze_page_vma(struct vm_area_struct *vma, struct page *page,
unsigned long address)
{
+ unsigned long haddr = address & HPAGE_PMD_MASK;
spinlock_t *ptl;
pgd_t *pgd;
pud_t *pud;
@@ -3136,34 +3137,48 @@ static void freeze_page_vma(struct vm_area_struct *vma, struct page *page,
}
if (pmd_trans_huge(*pmd)) {
if (page == pmd_page(*pmd))
- __split_huge_pmd_locked(vma, pmd, address, true);
+ __split_huge_pmd_locked(vma, pmd, haddr, true);
spin_unlock(ptl);
return;
}
spin_unlock(ptl);
pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl);
- for (i = 0; i < HPAGE_PMD_NR; i++, address += PAGE_SIZE, page++) {
+ for (i = 0; i < HPAGE_PMD_NR;
+ i++, address += PAGE_SIZE, page++, pte++) {
pte_t entry, swp_pte;
swp_entry_t swp_entry;
- if (!pte_present(pte[i]))
+ /*
+ * We've just crossed page table boundary: need to map next one.
+ * It can happen if THP was mremaped to non PMD-aligned address.
+ */
+ if (unlikely(address == haddr + HPAGE_PMD_SIZE)) {
+ pte_unmap_unlock(pte - 1, ptl);
+ pmd = mm_find_pmd(vma->vm_mm, address);
+ if (!pmd)
+ return;
+ pte = pte_offset_map_lock(vma->vm_mm, pmd,
+ address, &ptl);
+ }
+
+ if (!pte_present(*pte))
continue;
- if (page_to_pfn(page) != pte_pfn(pte[i]))
+ if (page_to_pfn(page) != pte_pfn(*pte))
continue;
flush_cache_page(vma, address, page_to_pfn(page));
- entry = ptep_clear_flush(vma, address, pte + i);
+ entry = ptep_clear_flush(vma, address, pte);
if (pte_dirty(entry))
SetPageDirty(page);
swp_entry = make_migration_entry(page, pte_write(entry));
swp_pte = swp_entry_to_pte(swp_entry);
if (pte_soft_dirty(entry))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
- set_pte_at(vma->vm_mm, address, pte + i, swp_pte);
+ set_pte_at(vma->vm_mm, address, pte, swp_pte);
page_remove_rmap(page, false);
put_page(page);
}
- pte_unmap_unlock(pte, ptl);
+ pte_unmap_unlock(pte - 1, ptl);
}
static void freeze_page(struct anon_vma *anon_vma, struct page *page)
@@ -3175,14 +3190,13 @@ static void freeze_page(struct anon_vma *anon_vma, struct page *page)
anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff,
pgoff + HPAGE_PMD_NR - 1) {
- unsigned long haddr;
+ unsigned long address = __vma_address(page, avc->vma);
- haddr = __vma_address(page, avc->vma) & HPAGE_PMD_MASK;
mmu_notifier_invalidate_range_start(avc->vma->vm_mm,
- haddr, haddr + HPAGE_PMD_SIZE);
- freeze_page_vma(avc->vma, page, haddr);
+ address, address + HPAGE_PMD_SIZE);
+ freeze_page_vma(avc->vma, page, address);
mmu_notifier_invalidate_range_end(avc->vma->vm_mm,
- haddr, haddr + HPAGE_PMD_SIZE);
+ address, address + HPAGE_PMD_SIZE);
}
}
@@ -3193,17 +3207,33 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
pmd_t *pmd;
pte_t *pte, entry;
swp_entry_t swp_entry;
+ unsigned long haddr = address & HPAGE_PMD_MASK;
int i;
pmd = mm_find_pmd(vma->vm_mm, address);
if (!pmd)
return;
+
pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl);
- for (i = 0; i < HPAGE_PMD_NR; i++, address += PAGE_SIZE, page++) {
- if (!is_swap_pte(pte[i]))
+ for (i = 0; i < HPAGE_PMD_NR;
+ i++, address += PAGE_SIZE, page++, pte++) {
+ /*
+ * We've just crossed page table boundary: need to map next one.
+ * It can happen if THP was mremaped to non-PMD aligned address.
+ */
+ if (unlikely(address == haddr + HPAGE_PMD_SIZE)) {
+ pte_unmap_unlock(pte - 1, ptl);
+ pmd = mm_find_pmd(vma->vm_mm, address);
+ if (!pmd)
+ return;
+ pte = pte_offset_map_lock(vma->vm_mm, pmd,
+ address, &ptl);
+ }
+
+ if (!is_swap_pte(*pte))
continue;
- swp_entry = pte_to_swp_entry(pte[i]);
+ swp_entry = pte_to_swp_entry(*pte);
if (!is_migration_entry(swp_entry))
continue;
if (migration_entry_to_page(swp_entry) != page)
@@ -3219,12 +3249,12 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
entry = maybe_mkwrite(entry, vma);
flush_dcache_page(page);
- set_pte_at(vma->vm_mm, address, pte + i, entry);
+ set_pte_at(vma->vm_mm, address, pte, entry);
/* No need to invalidate - it was non-present before */
- update_mmu_cache(vma, address, pte + i);
+ update_mmu_cache(vma, address, pte);
}
- pte_unmap_unlock(pte, ptl);
+ pte_unmap_unlock(pte - 1, ptl);
}
static void unfreeze_page(struct anon_vma *anon_vma, struct page *page)
@@ -3430,7 +3460,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
spin_lock(&split_queue_lock);
count = page_count(head);
mapcount = total_mapcount(head);
- if (mapcount == count - 1) {
+ if (!mapcount && count == 1) {
if (!list_empty(page_deferred_list(head))) {
split_queue_len--;
list_del(page_deferred_list(head));
@@ -3438,13 +3468,13 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
spin_unlock(&split_queue_lock);
__split_huge_page(page, list);
ret = 0;
- } else if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount > count - 1) {
+ } else if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
spin_unlock(&split_queue_lock);
pr_alert("total_mapcount: %u, page_count(): %u\n",
mapcount, count);
if (PageTail(page))
dump_page(head, NULL);
- dump_page(page, "total_mapcount(head) > page_count(head) - 1");
+ dump_page(page, "total_mapcount(head) > 0");
BUG();
} else {
spin_unlock(&split_queue_lock);
--
2.6.4
--
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