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authorPavel Tatashin <pasha.tatashin@oracle.com>2017-08-18 15:16:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-08-18 15:32:01 -0700
commit3010f876500f9ba921afaeccec30c45ca6584dc8 (patch)
tree61f656b6b3f56459f27cb11944102bf3dfcc162b /mm/page_alloc.c
parent768dc4e48420955518974d8486c1b00ec05e7274 (diff)
downloadop-kernel-dev-3010f876500f9ba921afaeccec30c45ca6584dc8.zip
op-kernel-dev-3010f876500f9ba921afaeccec30c45ca6584dc8.tar.gz
mm: discard memblock data later
There is existing use after free bug when deferred struct pages are enabled: The memblock_add() allocates memory for the memory array if more than 128 entries are needed. See comment in e820__memblock_setup(): * The bootstrap memblock region count maximum is 128 entries * (INIT_MEMBLOCK_REGIONS), but EFI might pass us more E820 entries * than that - so allow memblock resizing. This memblock memory is freed here: free_low_memory_core_early() We access the freed memblock.memory later in boot when deferred pages are initialized in this path: deferred_init_memmap() for_each_mem_pfn_range() __next_mem_pfn_range() type = &memblock.memory; One possible explanation for why this use-after-free hasn't been hit before is that the limit of INIT_MEMBLOCK_REGIONS has never been exceeded at least on systems where deferred struct pages were enabled. Tested by reducing INIT_MEMBLOCK_REGIONS down to 4 from the current 128, and verifying in qemu that this code is getting excuted and that the freed pages are sane. Link: http://lkml.kernel.org/r/1502485554-318703-2-git-send-email-pasha.tatashin@oracle.com Fixes: 7e18adb4f80b ("mm: meminit: initialise remaining struct pages in parallel with kswapd") Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com> Reviewed-by: Steven Sistare <steven.sistare@oracle.com> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Bob Picco <bob.picco@oracle.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page_alloc.c')
-rw-r--r--mm/page_alloc.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d00f74..1bad301 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1584,6 +1584,10 @@ void __init page_alloc_init_late(void)
/* Reinit limits that are based on free pages after the kernel is up */
files_maxfiles_init();
#endif
+#ifdef CONFIG_ARCH_DISCARD_MEMBLOCK
+ /* Discard memblock private memory */
+ memblock_discard();
+#endif
for_each_populated_zone(zone)
set_zone_contiguous(zone);
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