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