[PATCH 2/3] kasan: use apply_to_existing_pages for releasing vmalloc shadow

[Daniel Axtens <dja@axtens.net>]

kasan_release_vmalloc uses apply_to_page_range to release vmalloc
shadow. Unfortunately, apply_to_page_range can allocate memory to
fill in page table entries, which is not what we want.

Also, kasan_release_vmalloc is called under free_vmap_area_lock,
so if apply_to_page_range does allocate memory, we get a 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

Switch to using the apply_to_existing_pages helper instead, which
won't allocate memory.

Fixes: 3c5c3cfb9ef4 ("kasan: support backing vmalloc space with real shadow memory")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>

---

Andrew, if you want to take this, it replaces
"kasan: Don't allocate page tables in kasan_release_vmalloc()"
---
 mm/kasan/common.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index e04e73603dfc..26fd0c13dd28 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -957,6 +957,7 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
 {
 	void *shadow_start, *shadow_end;
 	unsigned long region_start, region_end;
+	unsigned long size;
 
 	region_start = ALIGN(start, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
 	region_end = ALIGN_DOWN(end, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
@@ -979,9 +980,10 @@ 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);
+		size = shadow_end - shadow_start;
+		apply_to_existing_pages(&init_mm, (unsigned long)shadow_start,
+					size, kasan_depopulate_vmalloc_pte,
+					NULL);
 		flush_tlb_kernel_range((unsigned long)shadow_start,
 				       (unsigned long)shadow_end);
 	}
-- 
2.20.1