[PATCH] mm/kasan: Don't vfree() nonexistent vm_area.

* [PATCH] mm/kasan: Don't vfree() nonexistent vm_area.
       [not found] <12c9e499-9c11-d248-6a3f-14ec8c4e07f1@molgen.mpg.de>
@ 2018-02-01 16:33 ` Andrey Ryabinin
  2018-02-01 19:57   ` Matthew Wilcox
                     ` (2 more replies)
  0 siblings, 3 replies; 16+ messages in thread
From: Andrey Ryabinin @ 2018-02-01 16:33 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Paul Menzel, Alexander Potapenko, Dmitry Vyukov, kasan-dev,
	linux-kernel, linux-mm, Andrey Ryabinin, stable

KASAN uses different routines to map shadow for hot added memory and memory
obtained in boot process. Attempt to offline memory onlined by normal boot
process leads to this:

    Trying to vfree() nonexistent vm area (000000005d3b34b9)
    WARNING: CPU: 2 PID: 13215 at mm/vmalloc.c:1525 __vunmap+0x147/0x190

    Call Trace:
     kasan_mem_notifier+0xad/0xb9
     notifier_call_chain+0x166/0x260
     __blocking_notifier_call_chain+0xdb/0x140
     __offline_pages+0x96a/0xb10
     memory_subsys_offline+0x76/0xc0
     device_offline+0xb8/0x120
     store_mem_state+0xfa/0x120
     kernfs_fop_write+0x1d5/0x320
     __vfs_write+0xd4/0x530
     vfs_write+0x105/0x340
     SyS_write+0xb0/0x140

Obviously we can't call vfree() to free memory that wasn't allocated via
vmalloc(). Use find_vm_area() to see if we can call vfree().

Unfortunately it's a bit tricky to properly unmap and free shadow allocated
during boot, so we'll have to keep it. If memory will come online again
that shadow will be reused.

Fixes: fa69b5989bb0 ("mm/kasan: add support for memory hotplug")
Reported-by: Paul Menzel <pmenzel+linux-kasan-dev@molgen.mpg.de>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: <stable@vger.kernel.org>
---
 mm/kasan/kasan.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 55 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index e13d911251e7..0d9d9d268f32 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -791,6 +791,41 @@ DEFINE_ASAN_SET_SHADOW(f5);
 DEFINE_ASAN_SET_SHADOW(f8);
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+static bool shadow_mapped(unsigned long addr)
+{
+	pgd_t *pgd = pgd_offset_k(addr);
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	if (pgd_none(*pgd))
+		return false;
+	p4d = p4d_offset(pgd, addr);
+	if (p4d_none(*p4d))
+		return false;
+	pud = pud_offset(p4d, addr);
+	if (pud_none(*pud))
+		return false;
+
+	/*
+	 * We can't use pud_large() or pud_huge(), the first one
+	 * is arch-specific, the last one depend on HUGETLB_PAGE.
+	 * So let's abuse pud_bad(), if bud is bad it's has to
+	 * because it's huge.
+	 */
+	if (pud_bad(*pud))
+		return true;
+	pmd = pmd_offset(pud, addr);
+	if (pmd_none(*pmd))
+		return false;
+
+	if (pmd_bad(*pmd))
+		return true;
+	pte = pte_offset_kernel(pmd, addr);
+	return !pte_none(*pte);
+}
+
 static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 			unsigned long action, void *data)
 {
@@ -812,6 +847,14 @@ static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 	case MEM_GOING_ONLINE: {
 		void *ret;
 
+		/*
+		 * If shadow is mapped already than it must have been mapped
+		 * during the boot. This could happen if we onlining previously
+		 * offlined memory.
+		 */
+		if (shadow_mapped(shadow_start))
+			return NOTIFY_OK;
+
 		ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
 					shadow_end, GFP_KERNEL,
 					PAGE_KERNEL, VM_NO_GUARD,
@@ -823,8 +866,18 @@ static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 		kmemleak_ignore(ret);
 		return NOTIFY_OK;
 	}
-	case MEM_OFFLINE:
-		vfree((void *)shadow_start);
+	case MEM_OFFLINE: {
+		struct vm_struct *vm;
+
+		/*
+		 * Only hot-added memory have vm_area. Freeing shadow
+		 * mapped during boot would be tricky, so we'll just
+		 * have to keep it.
+		 */
+		vm = find_vm_area((void *)shadow_start);
+		if (vm)
+			vfree((void *)shadow_start);
+	}
 	}
 
 	return NOTIFY_OK;
-- 
2.13.6

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