From de1c831a7898f164c1c2703c6b2b9e4fb4bebefc Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 15 Apr 2025 10:02:33 -0700 Subject: slab: Decouple slab_debug and no_hash_pointers 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 Reviewed-by: Harry Yoo Acked-by: Rafael Aquini Tested-by: Petr Mladek Reviewed-by: Petr Mladek Link: https://patch.msgid.link/20250415170232.it.467-kees@kernel.org [kees@kernel.org: Add note about hash_pointers into slab_debug kernel parameter documentation.] Signed-off-by: Petr Mladek --- lib/vsprintf.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 57 insertions(+), 4 deletions(-) (limited to 'lib') diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 01699852f30c..22cbd75266ef 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -60,6 +60,20 @@ bool no_hash_pointers __ro_after_init; EXPORT_SYMBOL_GPL(no_hash_pointers); +/* + * Hashed pointers policy selected by "hash_pointers=..." boot param + * + * `auto` - Hashed pointers enabled unless disabled by slub_debug_enabled=true + * `always` - Hashed pointers enabled unconditionally + * `never` - Hashed pointers disabled unconditionally + */ +enum hash_pointers_policy { + HASH_PTR_AUTO = 0, + HASH_PTR_ALWAYS, + HASH_PTR_NEVER +}; +static enum hash_pointers_policy hash_pointers_mode __initdata; + noinline static unsigned long long simple_strntoull(const char *startp, char **endp, unsigned int base, size_t max_chars) { @@ -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); /* -- cgit v1.2.3