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    Subject[34-longterm 163/179] mm: fix wrong vmap address calculations with odd NR_CPUS values
    Date
    From: Clemens Ladisch <clemens@ladisch.de>

    -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
    -------------------

    commit f982f91516fa4cfd9d20518833cd04ad714585be upstream.

    Commit db64fe02258f ("mm: rewrite vmap layer") introduced code that does
    address calculations under the assumption that VMAP_BLOCK_SIZE is a
    power of two. However, this might not be true if CONFIG_NR_CPUS is not
    set to a power of two.

    Wrong vmap_block index/offset values could lead to memory corruption.
    However, this has never been observed in practice (or never been
    diagnosed correctly); what caught this was the BUG_ON in vb_alloc() that
    checks for inconsistent vmap_block indices.

    To fix this, ensure that VMAP_BLOCK_SIZE always is a power of two.

    BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=31572
    Reported-by: Pavel Kysilka <goldenfish@linuxsoft.cz>
    Reported-by: Matias A. Fonzo <selk@dragora.org>
    Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
    Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
    Cc: Nick Piggin <npiggin@suse.de>
    Cc: Jeremy Fitzhardinge <jeremy@goop.org>
    Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    mm/vmalloc.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    index 20a402c..d44abdd 100644
    --- a/mm/vmalloc.c
    +++ b/mm/vmalloc.c
    @@ -671,9 +671,10 @@ static void free_unmap_vmap_area_addr(unsigned long addr)
    #define VMAP_BBMAP_BITS_MIN (VMAP_MAX_ALLOC*2)
    #define VMAP_MIN(x, y) ((x) < (y) ? (x) : (y)) /* can't use min() */
    #define VMAP_MAX(x, y) ((x) > (y) ? (x) : (y)) /* can't use max() */
    -#define VMAP_BBMAP_BITS VMAP_MIN(VMAP_BBMAP_BITS_MAX, \
    - VMAP_MAX(VMAP_BBMAP_BITS_MIN, \
    - VMALLOC_PAGES / NR_CPUS / 16))
    +#define VMAP_BBMAP_BITS \
    + VMAP_MIN(VMAP_BBMAP_BITS_MAX, \
    + VMAP_MAX(VMAP_BBMAP_BITS_MIN, \
    + VMALLOC_PAGES / roundup_pow_of_two(NR_CPUS) / 16))

    #define VMAP_BLOCK_SIZE (VMAP_BBMAP_BITS * PAGE_SIZE)

    --
    1.7.9.6


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