From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Subject: mm/kasan: don't vfree() nonexistent vm_area
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.
Matthew asked: how can you call vfree() on something that isn't a
vmalloc address?
vfree() is able to free any address returned by
__vmalloc_node_range(). And __vmalloc_node_range() gives you any
address you ask. It doesn't have to be an address in [VMALLOC_START,
VMALLOC_END] range.
That's also how the module_alloc()/module_memfree() works on
architectures that have designated area for modules.
[aryabinin@xxxxxxxxxxxxx: improve comments]
Link: http://lkml.kernel.org/r/dabee6ab-3a7a-51cd-3b86-5468718e0390@xxxxxxxxxxxxx
[akpm@xxxxxxxxxxxxxxxxxxxx: fix typos, reflow comment]
Link: http://lkml.kernel.org/r/20180201163349.8700-1-aryabinin@xxxxxxxxxxxxx
Fixes: fa69b5989bb0 ("mm/kasan: add support for memory hotplug")
Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Reported-by: Paul Menzel <pmenzel+linux-kasan-dev@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kasan/kasan.c | 63 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 61 insertions(+), 2 deletions(-)
diff -puN mm/kasan/kasan.c~mm-kasan-dont-vfree-nonexistent-vm_area mm/kasan/kasan.c
--- a/mm/kasan/kasan.c~mm-kasan-dont-vfree-nonexistent-vm_area
+++ a/mm/kasan/kasan.c
@@ -792,6 +792,40 @@ 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 depends on HUGETLB_PAGE. So let's abuse
+ * pud_bad(), if pud is bad then it's bad 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)
{
@@ -813,6 +847,14 @@ static int __meminit kasan_mem_notifier(
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,
@@ -824,8 +866,25 @@ static int __meminit kasan_mem_notifier(
kmemleak_ignore(ret);
return NOTIFY_OK;
}
- case MEM_OFFLINE:
- vfree((void *)shadow_start);
+ case MEM_OFFLINE: {
+ struct vm_struct *vm;
+
+ /*
+ * shadow_start was either mapped during boot by kasan_init()
+ * or during memory online by __vmalloc_node_range().
+ * In the latter case we can use vfree() to free shadow.
+ * Non-NULL result of the find_vm_area() will tell us if
+ * that was the second case.
+ *
+ * Currently it's not possible to free shadow mapped
+ * during boot by kasan_init(). It's because the code
+ * to do that hasn't been written yet. So we'll just
+ * leak the memory.
+ */
+ vm = find_vm_area((void *)shadow_start);
+ if (vm)
+ vfree((void *)shadow_start);
+ }
}
return NOTIFY_OK;
_
--
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