Clearling bits on cyclic buffer can overrun the cyclic buffer according to some combination of MAX_ORDER and cyclic buffer size.
The cyclic buffer size is corrected if possible. Signed-off-by: HATAYAMA Daisuke <[email protected]> --- makedumpfile.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 files changed, 70 insertions(+), 1 deletions(-) diff --git a/makedumpfile.c b/makedumpfile.c index 65b9fd7..18a1e0a 100644 --- a/makedumpfile.c +++ b/makedumpfile.c @@ -58,6 +58,7 @@ do { \ *ptr_long_table = value; \ } while (0) +static void check_cyclic_buffer_overrun(void); static void setup_page_is_buddy(void); void @@ -2832,6 +2833,9 @@ out: !sadump_generate_elf_note_from_dumpfile()) return FALSE; + if (info->flag_cyclic && info->dump_level & DL_EXCLUDE_FREE) + check_cyclic_buffer_overrun(); + } else { if (!get_mem_map_without_mm()) return FALSE; @@ -3669,6 +3673,61 @@ exclude_free_page(void) } /* + * Let C be a cyclic buffer size and B a bitmap size used for + * representing maximum block size managed by buddy allocator. + * + * For some combinations of C and B, clearing operation can overrun + * the cyclic buffer. Let's consider three cases. + * + * - If C == B, this is trivially safe. + * + * - If B > C, overrun can easily happen. + * + * - In case of C > B, if C mod B != 0, then there exist n > m > 0, + * B > b > 0 such that n x C = m x B + b. This means that clearing + * operation overruns cyclic buffer (B - b)-bytes in the + * combination of n-th cycle and m-th block. + * + * Note that C mod B != 0 iff (m x C) mod B != 0 for some m. + * + * If C == B, C mod B == 0 always holds. Again, if B > C, C mod B != 0 + * always holds. Hence, it's always sufficient to check the condition + * C mod B != 0 in order to determine whether overrun can happen or + * not. + * + * The bitmap size used for maximum block size B is calculated from + * MAX_ORDER as: + * + * B := DIVIDE_UP((1 << (MAX_ORDER - 1)), BITS_PER_BYTE) + * + * Normally, MAX_ORDER is 11 at default. This is configurable through + * CONFIG_FORCE_MAX_ZONEORDER. + */ +static void +check_cyclic_buffer_overrun(void) +{ + int max_order = ARRAY_LENGTH(zone.free_area); + int max_order_nr_pages = 1 << (max_order - 1); + unsigned long max_block_size = roundup(max_order_nr_pages, BITPERBYTE); + + if (info->bufsize_cyclic % + roundup(max_order_nr_pages, BITPERBYTE)) { + unsigned long bufsize; + + if (max_block_size > info->bufsize_cyclic) { + MSG("WARNING: some free pages are not filtered.\n"); + return; + } + + bufsize = info->bufsize_cyclic; + info->bufsize_cyclic = round(bufsize, max_block_size); + + MSG("cyclic buffer size has been changed: %lu => %lu\n", + bufsize, info->bufsize_cyclic); + } +} + +/* * For the kernel versions from v2.6.15 to v2.6.17. */ static int @@ -4013,8 +4072,18 @@ __exclude_unnecessary_pages(unsigned long mem_map, && info->page_is_buddy(flags, _mapcount, private, _count)) { int i; - for (i = 0; i < (1 << private); ++i) + for (i = 0; i < (1 << private); ++i) { + /* + * According to combination of + * MAX_ORDER and size of cyclic + * buffer, this clearing bit operation + * can overrun the cyclic buffer. + * + * See check_cyclic_buffer_overrun() + * for the detail. + */ clear_bit_on_2nd_bitmap_for_kernel(pfn + i); + } pfn_free += i; } /* _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
