[PATCH 2/2] kasan: Don't allocate page tables in kasan_release_vmalloc()

Andrey Ryabinin
2019-12-04T20:46:16Z

The purpose of kasan_release_vmalloc() is to unmap and deallocate shadow
memory. The usage of apply_to_page_range() isn't suitable in that scenario
because it allocates pages to fill missing page tables entries.
This also cause sleep in atomic bug:

BUG: sleeping function called from invalid context at mm/page_alloc.c:4681
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 15087, name:

Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x199/0x216 lib/dump_stack.c:118
___might_sleep.cold.97+0x1f5/0x238 kernel/sched/core.c:6800
__might_sleep+0x95/0x190 kernel/sched/core.c:6753
prepare_alloc_pages mm/page_alloc.c:4681 [inline]
__alloc_pages_nodemask+0x3cd/0x890 mm/page_alloc.c:4730
alloc_pages_current+0x10c/0x210 mm/mempolicy.c:2211
alloc_pages include/linux/gfp.h:532 [inline]
__get_free_pages+0xc/0x40 mm/page_alloc.c:4786
__pte_alloc_one_kernel include/asm-generic/pgalloc.h:21 [inline]
pte_alloc_one_kernel include/asm-generic/pgalloc.h:33 [inline]
__pte_alloc_kernel+0x1d/0x200 mm/memory.c:459
apply_to_pte_range mm/memory.c:2031 [inline]
apply_to_pmd_range mm/memory.c:2068 [inline]
apply_to_pud_range mm/memory.c:2088 [inline]
apply_to_p4d_range mm/memory.c:2108 [inline]
apply_to_page_range+0x77d/0xa00 mm/memory.c:2133
kasan_release_vmalloc+0xa7/0xc0 mm/kasan/common.c:970
__purge_vmap_area_lazy+0xcbb/0x1f30 mm/vmalloc.c:1313
try_purge_vmap_area_lazy mm/vmalloc.c:1332 [inline]
free_vmap_area_noflush+0x2ca/0x390 mm/vmalloc.c:1368
free_unmap_vmap_area mm/vmalloc.c:1381 [inline]
remove_vm_area+0x1cc/0x230 mm/vmalloc.c:2209
vm_remove_mappings mm/vmalloc.c:2236 [inline]
__vunmap+0x223/0xa20 mm/vmalloc.c:2299
__vfree+0x3f/0xd0 mm/vmalloc.c:2356
__vmalloc_area_node mm/vmalloc.c:2507 [inline]
__vmalloc_node_range+0x5d5/0x810 mm/vmalloc.c:2547
__vmalloc_node mm/vmalloc.c:2607 [inline]
__vmalloc_node_flags mm/vmalloc.c:2621 [inline]
vzalloc+0x6f/0x80 mm/vmalloc.c:2666
alloc_one_pg_vec_page net/packet/af_packet.c:4233 [inline]
alloc_pg_vec net/packet/af_packet.c:4258 [inline]
packet_set_ring+0xbc0/0x1b50 net/packet/af_packet.c:4342
packet_setsockopt+0xed7/0x2d90 net/packet/af_packet.c:3695
__sys_setsockopt+0x29b/0x4d0 net/socket.c:2117
__do_sys_setsockopt net/socket.c:2133 [inline]
__se_sys_setsockopt net/socket.c:2130 [inline]
__x64_sys_setsockopt+0xbe/0x150 net/socket.c:2130
do_syscall_64+0xfa/0x780 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Add kasan_unmap_page_range() which skips empty page table entries instead
of allocating them.

Fixes: 3c5c3cfb9ef4 ("kasan: support backing vmalloc space with real shadow memory")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
mm/kasan/common.c | 82 +++++++++++++++++++++++++++++++++++++++--------
1 file changed, 68 insertions(+), 14 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index a1e6273be8c3..e9ba7d8ad324 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -857,22 +857,77 @@ void kasan_unpoison_vmalloc(const void *start, unsigned long size)
kasan_unpoison_shadow(start, size);
}

-static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
- void *unused)
+static void kasan_unmap_pte_range(pmd_t *pmd, unsigned long addr,
+ unsigned long end)
{
- unsigned long page;
+ pte_t *pte;

- page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);
+ pte = pte_offset_kernel(pmd, addr);
+ do {
+ pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);

- spin_lock(&init_mm.page_table_lock);
+ if (!pte_none(ptent))
+ __free_page(pte_page(ptent));
+ } while (pte++, addr += PAGE_SIZE, addr != end);
+}

- if (likely(!pte_none(*ptep))) {
- pte_clear(&init_mm, addr, ptep);
- free_page(page);
- }
- spin_unlock(&init_mm.page_table_lock);
+static void kasan_unmap_pmd_range(pud_t *pud, unsigned long addr,
+ unsigned long end)
+{
+ pmd_t *pmd;
+ unsigned long next;

- return 0;
+ pmd = pmd_offset(pud, addr);
+ do {
+ next = pmd_addr_end(addr, end);
+ if (pmd_none_or_clear_bad(pmd))
+ continue;
+ kasan_unmap_pte_range(pmd, addr, next);
+ } while (pmd++, addr = next, addr != end);
+}
+
+static void kasan_unmap_pud_range(p4d_t *p4d, unsigned long addr,
+ unsigned long end)
+{
+ pud_t *pud;
+ unsigned long next;
+
+ pud = pud_offset(p4d, addr);
+ do {
+ next = pud_addr_end(addr, end);
+ if (pud_none_or_clear_bad(pud))
+ continue;
+ kasan_unmap_pmd_range(pud, addr, next);
+ } while (pud++, addr = next, addr != end);
+}
+
+static void kasan_unmap_p4d_range(pgd_t *pgd, unsigned long addr,
+ unsigned long end)
+{
+ p4d_t *p4d;
+ unsigned long next;
+
+ p4d = p4d_offset(pgd, addr);
+ do {
+ next = p4d_addr_end(addr, end);
+ if (p4d_none_or_clear_bad(p4d))
+ continue;
+ kasan_unmap_pud_range(p4d, addr, next);
+ } while (p4d++, addr = next, addr != end);
+}
+
+static void kasan_unmap_page_range(unsigned long addr, unsigned long end)
+{
+ pgd_t *pgd;
+ unsigned long next;
+
+ pgd = pgd_offset_k(addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ if (pgd_none_or_clear_bad(pgd))
+ continue;
+ kasan_unmap_p4d_range(pgd, addr, next);
+ } while (pgd++, addr = next, addr != end);
}

/*
@@ -978,9 +1033,8 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
shadow_end = kasan_mem_to_shadow((void *)region_end);

if (shadow_end > shadow_start) {
- apply_to_page_range(&init_mm, (unsigned long)shadow_start,
- (unsigned long)(shadow_end - shadow_start),
- kasan_depopulate_vmalloc_pte, NULL);
+ kasan_unmap_page_range((unsigned long)shadow_start,
+ (unsigned long)shadow_end);
flush_tlb_kernel_range((unsigned long)shadow_start,
(unsigned long)shadow_end);
}
--
2.23.0