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Commit 3010f876 authored by Pavel Tatashin's avatar Pavel Tatashin Committed by Linus Torvalds
Browse files

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: 7e18adb4 ("mm: meminit: initialise remaining struct pages in parallel with kswapd")
Signed-off-by: default avatarPavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: default avatarSteven Sistare <steven.sistare@oracle.com>
Reviewed-by: default avatarDaniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: default avatarBob Picco <bob.picco@oracle.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 768dc4e4

include/linux/memblock.h

+4 −2
Original line number Diff line number Diff line
@@ -61,6 +61,7 @@ extern int memblock_debug; 
#ifdef CONFIG_ARCH_DISCARD_MEMBLOCK

#define __init_memblock __meminit

#define __initdata_memblock __meminitdata

void memblock_discard(void);

#else

#define __init_memblock

#define __initdata_memblock
@@ -74,8 +75,6 @@ phys_addr_t memblock_find_in_range_node(phys_addr_t size, phys_addr_t align, 
					int nid, ulong flags);

phys_addr_t memblock_find_in_range(phys_addr_t start, phys_addr_t end,

				   phys_addr_t size, phys_addr_t align);

phys_addr_t get_allocated_memblock_reserved_regions_info(phys_addr_t *addr);

phys_addr_t get_allocated_memblock_memory_regions_info(phys_addr_t *addr);

void memblock_allow_resize(void);

int memblock_add_node(phys_addr_t base, phys_addr_t size, int nid);

int memblock_add(phys_addr_t base, phys_addr_t size);
@@ -110,6 +109,9 @@ void __next_mem_range_rev(u64 *idx, int nid, ulong flags, 
void __next_reserved_mem_region(u64 *idx, phys_addr_t *out_start,

				phys_addr_t *out_end);



void __memblock_free_early(phys_addr_t base, phys_addr_t size);

void __memblock_free_late(phys_addr_t base, phys_addr_t size);



/**

 * for_each_mem_range - iterate through memblock areas from type_a and not

 * included in type_b. Or just type_a if type_b is NULL.

mm/memblock.c

+17 −21
Original line number Diff line number Diff line
@@ -285,31 +285,27 @@ static void __init_memblock memblock_remove_region(struct memblock_type *type, u 
}



#ifdef CONFIG_ARCH_DISCARD_MEMBLOCK



phys_addr_t __init_memblock get_allocated_memblock_reserved_regions_info(

					phys_addr_t *addr)

/**

 * Discard memory and reserved arrays if they were allocated

 */

void __init memblock_discard(void)

{

	if (memblock.reserved.regions == memblock_reserved_init_regions)

		return 0;



	*addr = __pa(memblock.reserved.regions);

	phys_addr_t addr, size;



	return PAGE_ALIGN(sizeof(struct memblock_region) *

	if (memblock.reserved.regions != memblock_reserved_init_regions) {

		addr = __pa(memblock.reserved.regions);

		size = PAGE_ALIGN(sizeof(struct memblock_region) *

				  memblock.reserved.max);

		__memblock_free_late(addr, size);

	}



phys_addr_t __init_memblock get_allocated_memblock_memory_regions_info(

					phys_addr_t *addr)

{

	if (memblock.memory.regions == memblock_memory_init_regions)

		return 0;



	*addr = __pa(memblock.memory.regions);



	return PAGE_ALIGN(sizeof(struct memblock_region) *

	if (memblock.memory.regions == memblock_memory_init_regions) {

		addr = __pa(memblock.memory.regions);

		size = PAGE_ALIGN(sizeof(struct memblock_region) *

				  memblock.memory.max);

		__memblock_free_late(addr, size);

	}

}



#endif



/**

mm/nobootmem.c

+0 −16
Original line number Diff line number Diff line
@@ -146,22 +146,6 @@ static unsigned long __init free_low_memory_core_early(void) 
				NULL)

		count += __free_memory_core(start, end);



#ifdef CONFIG_ARCH_DISCARD_MEMBLOCK

	{

		phys_addr_t size;



		/* Free memblock.reserved array if it was allocated */

		size = get_allocated_memblock_reserved_regions_info(&start);

		if (size)

			count += __free_memory_core(start, start + size);



		/* Free memblock.memory array if it was allocated */

		size = get_allocated_memblock_memory_regions_info(&start);

		if (size)

			count += __free_memory_core(start, start + size);

	}

#endif



	return count;

}

mm/page_alloc.c

+4 −0
Original line number Diff line number Diff line
@@ -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);