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    Subject[PATCH] mm/slab_common.c: fix possible spectre-v1 in kmalloc_slab()
    Date
    The `size` in kmalloc_slab() is indirectly controlled by userspace via syscall: poll(defined in fs/select.c), hence leading to a potential exploitation of the Spectre variant 1 vulnerability.
    The `size` can be controlled from: poll -> do_sys_poll -> kmalloc -> __kmalloc -> kmalloc_slab.

    Fix this by sanitizing `size` before using it to index size_index.

    Signed-off-by: Dianzhang Chen <dianzhangchen0@gmail.com>
    ---
    mm/slab_common.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/mm/slab_common.c b/mm/slab_common.c
    index 58251ba..41c7e34 100644
    --- a/mm/slab_common.c
    +++ b/mm/slab_common.c
    @@ -21,6 +21,7 @@
    #include <asm/tlbflush.h>
    #include <asm/page.h>
    #include <linux/memcontrol.h>
    +#include <linux/nospec.h>

    #define CREATE_TRACE_POINTS
    #include <trace/events/kmem.h>
    @@ -1056,6 +1057,7 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
    if (!size)
    return ZERO_SIZE_PTR;

    + size = array_index_nospec(size, 193);
    index = size_index[size_index_elem(size)];
    } else {
    if (WARN_ON_ONCE(size > KMALLOC_MAX_CACHE_SIZE))
    --
    2.7.4
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