Messages in this thread Patch in this message | | | Date | Wed, 16 Apr 2008 02:03:56 +0200 | From | Ingo Molnar <> | Subject | [patch] mm: sparsemem memory_present() memory corruption fix |
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finally found it ... the patch below solves the sparsemem crash and the testsystem boots up fine now:
mars:~> uname -a Linux mars 2.6.25-rc9-sched-devel.git-x86-latest.git #985 SMP Wed Apr 16 01:37:37 CEST 2008 i686 i686 i386 GNU/Linux
yay! :-)
Ingo
ps. anyone who can correctly guess the method with which i found the exact place that corrupted memory will get a free beer next time we meet :-)
-------------------------> Subject: mm: sparsemem memory_present() memory corruption fix From: Ingo Molnar <mingo@elte.hu> Date: Wed Apr 16 01:40:00 CEST 2008
fix memory corruption and crash on 32-bit x86 systems.
if a !PAE x86 kernel is booted on a 32-bit system with more than 4GB of RAM, then we call memory_present() with a start/end that goes outside the scope of MAX_PHYSMEM_BITS.
that causes this loop to happily walk over the limit of the sparse memory section map:
for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) { unsigned long section = pfn_to_section_nr(pfn); struct mem_section *ms;
sparse_index_init(section, nid); set_section_nid(section, nid);
ms = __nr_to_section(section); if (!ms->section_mem_map) ms->section_mem_map = sparse_encode_early_nid(nid) |
'ms' will be out of bounds and we'll corrupt a small amount of memory by encoding the node ID. Depending on what that memory is, we might crash, misbehave or just not notice the bug.
the fix is to sanity check anything the architecture passes to sparsemem.
this bug seems to be rather old (as old as sparsemem support itself), but the exact incarnation depended on random details like configs, which made this bug more prominent in v2.6.25-to-be.
an additional enhancement might be to print a warning about ignored or trimmed memory ranges.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- mm/sparse.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
Index: linux/mm/sparse.c =================================================================== --- linux.orig/mm/sparse.c +++ linux/mm/sparse.c @@ -149,8 +149,18 @@ static inline int sparse_early_nid(struc /* Record a memory area against a node. */ void __init memory_present(int nid, unsigned long start, unsigned long end) { + unsigned long max_arch_pfn = 1ULL << (MAX_PHYSMEM_BITS-PAGE_SHIFT); unsigned long pfn; + /* + * Sanity checks - do not allow an architecture to pass + * in larger pfns than the maximum scope of sparsemem: + */ + if (start >= max_arch_pfn) + return; + if (end >= max_arch_pfn) + end = max_arch_pfn; + start &= PAGE_SECTION_MASK; for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) { unsigned long section = pfn_to_section_nr(pfn);
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