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    Subject[PATCH] Revert "slub: force on no_hash_pointers when slub_debug is enabled"
    Date
    This reverts commit 792702911f581f7793962fbeb99d5c3a1b28f4c3.

    Linking no_hash_pointers() to slub_debug has had a chilling effect
    on using slub_debug features for security hardening, since system
    builders are forced to choose between redzoning and heap address location
    exposures. Instead, just require that the "no_hash_pointers" boot param
    needs to be used to expose pointers during slub_debug reports.

    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Stephen Boyd <swboyd@chromium.org>
    Cc: concord@gentoo.org
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Petr Mladek <pmladek@suse.com>
    Cc: linux-mm@kvack.org
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/
    Signed-off-by: Kees Cook <keescook@chromium.org>
    ---
    include/linux/kernel.h | 2 --
    lib/vsprintf.c | 2 +-
    mm/slub.c | 4 ----
    3 files changed, 1 insertion(+), 7 deletions(-)

    diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    index fe6efb24d151..e3d9d3879495 100644
    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -229,8 +229,6 @@ int sscanf(const char *, const char *, ...);
    extern __scanf(2, 0)
    int vsscanf(const char *, const char *, va_list);

    -extern int no_hash_pointers_enable(char *str);
    -
    extern int get_option(char **str, int *pint);
    extern char *get_options(const char *str, int nints, int *ints);
    extern unsigned long long memparse(const char *ptr, char **retptr);
    diff --git a/lib/vsprintf.c b/lib/vsprintf.c
    index be71a03c936a..410b4a80a58a 100644
    --- a/lib/vsprintf.c
    +++ b/lib/vsprintf.c
    @@ -2222,7 +2222,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
    return widen_string(buf, buf - buf_start, end, spec);
    }

    -int __init no_hash_pointers_enable(char *str)
    +static int __init no_hash_pointers_enable(char *str)
    {
    if (no_hash_pointers)
    return 0;
    diff --git a/mm/slub.c b/mm/slub.c
    index 13459c69095a..63f7337dd433 100644
    --- a/mm/slub.c
    +++ b/mm/slub.c
    @@ -5005,10 +5005,6 @@ void __init kmem_cache_init(void)
    if (debug_guardpage_minorder())
    slub_max_order = 0;

    - /* Print slub debugging pointers without hashing */
    - if (__slub_debug_enabled())
    - no_hash_pointers_enable(NULL);
    -
    kmem_cache_node = &boot_kmem_cache_node;
    kmem_cache = &boot_kmem_cache;

    --
    2.34.1
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