On Tue 2025-04-15 10:02:33, Kees Cook wrote: > Some system owners use slab_debug=FPZ (or similar) as a hardening option, > but do not want to be forced into having kernel addresses exposed due > to the implicit "no_hash_pointers" boot param setting.[1] > > Introduce the "hash_pointers" boot param, which defaults to "auto" > (the current behavior), but also includes "always" (forcing on hashing > even when "slab_debug=..." is defined), and "never". The existing > "no_hash_pointers" boot param becomes an alias for "hash_pointers=never". > > This makes it possible to boot with "slab_debug=FPZ hash_pointers=always". > > Link: https://github.com/KSPP/linux/issues/368 [1] > Fixes: 792702911f58 ("slub: force on no_hash_pointers when slub_debug is enabled") > Co-developed-by: Sergio Perez Gonzalez <sperezglz@xxxxxxxxx> > Signed-off-by: Sergio Perez Gonzalez <sperezglz@xxxxxxxxx> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> > Signed-off-by: Kees Cook <kees@xxxxxxxxxx> Tested-by: Petr Mladek <pmladek@xxxxxxxx> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> I am going to wait few more days for a potential feedback. I'll queue it for 6.16 unless anyone complains. See a rant below ;-) > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -2271,12 +2285,23 @@ char *resource_or_range(const char *fmt, char *buf, char *end, void *ptr, > return resource_string(buf, end, ptr, spec, fmt); > } > > -int __init no_hash_pointers_enable(char *str) > +void __init hash_pointers_finalize(bool slub_debug) > { > - if (no_hash_pointers) > - return 0; > + switch (hash_pointers_mode) { > + case HASH_PTR_ALWAYS: > + no_hash_pointers = false; > + break; > + case HASH_PTR_NEVER: > + no_hash_pointers = true; > + break; > + case HASH_PTR_AUTO: > + default: > + no_hash_pointers = slub_debug; > + break; > + } > > - no_hash_pointers = true; > + if (!no_hash_pointers) > + return; > > pr_warn("**********************************************************\n"); > pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); > @@ -2289,11 +2314,39 @@ int __init no_hash_pointers_enable(char *str) > pr_warn("** the kernel, report this immediately to your system **\n"); > pr_warn("** administrator! **\n"); > pr_warn("** **\n"); > + pr_warn("** Use hash_pointers=always to force this mode off **\n"); > + pr_warn("** **\n"); > pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n"); > pr_warn("**********************************************************\n"); > +} > + > +static int __init hash_pointers_mode_parse(char *str) > +{ > + if (!str) { > + pr_warn("Hash pointers mode empty; falling back to auto.\n"); > + hash_pointers_mode = HASH_PTR_AUTO; > + } else if (strncmp(str, "auto", 4) == 0) { > + pr_info("Hash pointers mode set to auto.\n"); > + hash_pointers_mode = HASH_PTR_AUTO; > + } else if (strncmp(str, "never", 5) == 0) { > + pr_info("Hash pointers mode set to never.\n"); > + hash_pointers_mode = HASH_PTR_NEVER; > + } else if (strncmp(str, "always", 6) == 0) { > + pr_info("Hash pointers mode set to always.\n"); > + hash_pointers_mode = HASH_PTR_ALWAYS; > + } else { > + pr_warn("Unknown hash_pointers mode '%s' specified; assuming auto.\n", str); > + hash_pointers_mode = HASH_PTR_AUTO; > + } > > return 0; > } > +early_param("hash_pointers", hash_pointers_mode_parse); > + > +static int __init no_hash_pointers_enable(char *str) > +{ > + return hash_pointers_mode_parse("never"); > +} > early_param("no_hash_pointers", no_hash_pointers_enable); I personally do not like that these two parameters do not have the real effect until hash_pointers_finalize() is called at some "random" "unrelated" location, namely kmem_cache_init(). But I could live with it. But the alternative solution proposed at https://lore.kernel.org/r/Z_0AFjai6Bvg-YLD@xxxxxxxxxxxxxxx was hairy another way. We could always improve it when it causes troubles. Best Regards, Petr
