On 2/8/23 20:47, Kees Cook wrote: > 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. Searching lore made me find [1] and I like the more concrete changelog as well as updated documentation. While it's convenient, it's probably indeed not slub's decision to enable no_hash_pointers. But Stephen also has a point in reply to [1]. If the data/address leak is indeed a concern, slub_debug will still print raw dumps as part of the reports, so will e.g. dump_page(), so hashing %p is not a complete solution and something more generic could be created for controlling prints that distinguishes hardening vs debugging? [1] https://lore.kernel.org/all/8e472c9e-2076-bc25-5912-8433adf7b579@xxxxxxxxxxxx/ > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx> > Cc: concord@xxxxxxxxxx > Cc: Pekka Enberg <penberg@xxxxxxxxxx> > Cc: David Rientjes <rientjes@xxxxxxxxxx> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Cc: Petr Mladek <pmladek@xxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: stable@xxxxxxxxxxxxxxx > Link: https://lore.kernel.org/lkml/202109200726.2EFEDC5@keescook/ > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > 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; >
