From: Andrey Ryabinin aryabinin@virtuozzo.com 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@virtuozzo.com: improve comments] Link: http://lkml.kernel.org/r/dabee6ab-3a7a-51cd-3b86-5468718e0390@virtuozzo.com [akpm@linux-foundation.org: fix typos, reflow comment] Link: http://lkml.kernel.org/r/20180201163349.8700-1-aryabinin@virtuozzo.com Fixes: fa69b5989bb0 ("mm/kasan: add support for memory hotplug") Signed-off-by: Andrey Ryabinin aryabinin@virtuozzo.com Reported-by: Paul Menzel pmenzel+linux-kasan-dev@molgen.mpg.de Cc: Alexander Potapenko glider@google.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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; _