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

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

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