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Wed, 16 Apr 2025 05:06:24 -0700 (PDT) Received: from pathway.suse.cz ([176.114.240.130]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39eae963f62sm16683914f8f.5.2025.04.16.05.06.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Apr 2025 05:06:23 -0700 (PDT) Date: Wed, 16 Apr 2025 14:06:21 +0200 From: Petr Mladek To: Kees Cook Cc: Sergio Perez Gonzalez , Vlastimil Babka , David Rientjes , Bagas Sanjaya , Jonathan Corbet , Steven Rostedt , Andy Shevchenko , Rasmus Villemoes , Sergey Senozhatsky , Andrew Morton , Christoph Lameter , Pekka Enberg , Joonsoo Kim , Roman Gushchin , Harry Yoo , "Paul E. McKenney" , Randy Dunlap , Tamir Duberstein , Miguel Ojeda , Alice Ryhl , linux-doc@vger.kernel.org, linux-mm@kvack.org, Thomas Huth , "Borislav Petkov (AMD)" , Ard Biesheuvel , Greg Kroah-Hartman , Andreas Hindborg , Stephen Boyd , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2] slab: Decouple slab_debug and no_hash_pointers Message-ID: References: <20250415170232.it.467-kees@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250415170232.it.467-kees@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: 74A9940004 X-Rspamd-Server: rspam04 X-Stat-Signature: hxife8597t4b7omwkeua454mb974zndy X-HE-Tag: 1744805191-985435 X-HE-Meta: U2FsdGVkX1+DU7goitPEvPGmiKNqQLvvypHQbxeY+LEhcogC/FH6D0FyvdA+oec9cHXKMxP/ZdMRrh4dGLLb59WCWkl+8A2FnO4AfwKP/bml+1fV4TEeGV7kFpmyn3k0ONpdVZ854JcK/cW+Z0BRpeaz9w6K2uHdjjhqz0wIhHUG4J86UnOCq0YmSi7/9Z0OmyqSdr41xZZoEtUfsplFy8MtfTOuOSRhRUBdP94kWhPUxN80Ce7aw9jDit8vv0p7fRqffhTGXXBeL+n140aCJ6WvXKlLbSwQo/ooe7Tc7uhAI9bKIs7vbHp3zOUa01OCXsjLpDRjNCB0PaTNcWyeT+3kK3vbthpSjYRvKuA91Jfr2zLH5i56OBugOqD0NWfbsWYIk29QkrACZcO3RYfAquervhopixAt+xROESToakfBiFu7VQEMPDp88XaDLithntxJb/F7jRfS15wuKnR15TTtjbZdKscULUb9jReSaOzIGdW+uy7epyVsxuTPKqh78TB1EAlZJbpLRP9r+dcIslGKSA4z7SQ7Vxym+UH04BJ5qmtI2PsF0gJfJ1sTtvTsvfnDbnWjjrEEug7be32X1a5mrdMRvtRJKQKUtwpCn3mJWTvA+NjFIWCKdg0AzqeD/piiSJuUkY6YgdJnh3QzRqZsd3VlJ3u3/XXTwJpBadQ/wC2cg5cajBDv37eLLDmCZt0CmJRoLnjLdZrRvWxpLjS3yXm8Z2zsyJqinHaZKjuSQ6F1605up3nhRbEuLRwf3DIYkML/WHQnREkLcC67Nhel6OnK2ylOFdB08x+lZPa8R3WqQUn1wfHulXhjJkhYSj6sJQGt19artyH0YezPuqUwEqNZEDJIUJHci9MIa2KBSmiGgPgWYVHrmw82BFAALZ02SqNxoIpP2RoM4/TIVxIg/OU48f+7868MDnZ0nxkZVThOkkIV3JkmCp6aXtf3X7cBYbJ8We7xIbp1Z6I 8Dn4oZ2z Nw6ElHqIx1Z0NLK5EgYqHNrxS9SOtMNIhODSXvI9i//sZJbuOUWMXfL/whUG1vFofo2CjzjLIOAin4a0Ot3PMtNWt0/BViecer26iQ7cafkNGz90ekEZdarZH0SKPc3ikCud34wNqkIVr4e1D+KY4okBJZwylfl+7QZosI1OLbgo4+gB41U9UNxpohidvVi2VNKKk85iKHbDETzjhhCISDQEWejobNzY2V2vA7k77RireuDeWp4iUMYkY7YS5WwFntFATV57cz7yiX+IKhIK3NTJUXXsNqpj6SfLedbR5FHAtN73T6UjIs2xrJaDBKsK6X8o8QL8vBDyTis3CatCmzCdxnVl5N+F3OrqP3J/WRKvalDkHlolDAvMgcW6CKCuq93NzGWdWJGJFIABtFSpGsS1DyRkYKaXcbOnj6VkiSwIFUTsKtq3uQ3KdMhAA48d6y32kBS5xN1NInFecMdKEr3YL/w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > Signed-off-by: Sergio Perez Gonzalez > Acked-by: Vlastimil Babka > Acked-by: David Rientjes > Reviewed-by: Bagas Sanjaya > Signed-off-by: Kees Cook Tested-by: Petr Mladek Reviewed-by: Petr Mladek 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@pathway.suse.cz was hairy another way. We could always improve it when it causes troubles. Best Regards, Petr