Patch "mm: discard memblock data later" has been added to the 4.12-stable tree

PATCH [email protected] 1 participant 1 message Aug 20, 2017

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Stable branch Memory management Page allocator memblock and memory management initialization

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2017-08-20 18:33 UTC #0 lore raw

This is a note to let you know that I've just added the patch titled

mm: discard memblock data later

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-discard-memblock-data-later.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 3010f876500f9ba921afaeccec30c45ca6584dc8 Mon Sep 17 00:00:00 2001

From: Pavel Tatashin <[email protected]>
Date: Fri, 18 Aug 2017 15:16:05 -0700
Subject: mm: discard memblock data later

From: Pavel Tatashin <[email protected]>

commit 3010f876500f9ba921afaeccec30c45ca6584dc8 upstream.

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/[email protected] open here

Fixes 7e18adb4f80b ("mm: meminit: initialise remaining struct pages in parallel with kswapd")

Signed-off-by Pavel Tatashin <[email protected]>

Reviewed-by Steven Sistare <[email protected]>

Reviewed-by Daniel Jordan <[email protected]>

Reviewed-by Bob Picco <[email protected]>

Acked-by Michal Hocko <[email protected]>

Cc Mel Gorman <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Signed-off-by Linus Torvalds <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 include/linux/memblock.h |    6 ++++--
 mm/memblock.c            |   40 ++++++++++++++++++----------------------
 mm/nobootmem.c           |   16 ----------------
 mm/page_alloc.c          |    4 ++++
 4 files changed, 26 insertions(+), 40 deletions(-)

include/linux/memblock.h +4 -2

@@ -65,6 +65,7 @@ extern bool movable_node_enabled;
 #ifdef CONFIG_ARCH_DISCARD_MEMBLOCK
 #define __init_memblock __meminit
 #define __initdata_memblock __meminitdata
+void memblock_discard(void);
 #else
 #define __init_memblock
 #define __initdata_memblock

@@ -78,8 +79,6 @@ phys_addr_t memblock_find_in_range_node(
 					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);

@@ -114,6 +113,9 @@ void __next_mem_range_rev(u64 *idx, int
 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 +18 ~~-22~~

@@ -288,31 +288,27 @@ static void __init_memblock memblock_rem
 }
 
 #ifdef CONFIG_ARCH_DISCARD_MEMBLOCK
-
-phys_addr_t __init_memblock get_allocated_memblock_reserved_regions_info(
-					phys_addr_t *addr)
-{
-	if (memblock.reserved.regions == memblock_reserved_init_regions)
-		return 0;
-
-	*addr = __pa(memblock.reserved.regions);
-
-	return PAGE_ALIGN(sizeof(struct memblock_region) *
-			  memblock.reserved.max);
-}
-
-phys_addr_t __init_memblock get_allocated_memblock_memory_regions_info(
-					phys_addr_t *addr)
+/**
+ * Discard memory and reserved arrays if they were allocated
+ */
+void __init memblock_discard(void)
 {
-	if (memblock.memory.regions == memblock_memory_init_regions)
-		return 0;
+	phys_addr_t addr, size;
 
-	*addr = __pa(memblock.memory.regions);
-
-	return PAGE_ALIGN(sizeof(struct memblock_region) *
-			  memblock.memory.max);
+	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);
+	}
+
+	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~~

@@ -146,22 +146,6 @@ static unsigned long __init free_low_mem
 				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

@@ -1582,6 +1582,10 @@ 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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/mm-discard-memblock-data-later.patch