From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B52FDC369AB for ; Mon, 21 Apr 2025 18:05:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 470D86B0005; Mon, 21 Apr 2025 14:05:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F8976B0007; Mon, 21 Apr 2025 14:05:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 24B9B6B0008; Mon, 21 Apr 2025 14:05:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 0075F6B0005 for ; Mon, 21 Apr 2025 14:05:18 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 7B9A75CC62 for ; Mon, 21 Apr 2025 18:05:19 +0000 (UTC) X-FDA: 83358827958.22.7C90252 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf13.hostedemail.com (Postfix) with ESMTP id 1D76420014 for ; Mon, 21 Apr 2025 18:05:16 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=jGWvZEXb; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of raquini@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=raquini@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1745258717; a=rsa-sha256; cv=none; b=BtGHWpfrYm7BzchMkcdidQZi6nj6xfNFRXWEgD42fmIHVVQZ38AzD1886xBQIrqHIvIKXH IppFSE23OZ85r8oinWoHAs4lkKUUwmmCu9Q8L1IIIm4wkLHooWLBL1GplPIsNxYLXQitEo O9zUY9hS/Qy6vHjYu/E2s2t7pMZgOz0= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=jGWvZEXb; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of raquini@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=raquini@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1745258717; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=eVvKIhcDUigy61iYir4MfxXVC274WCrw45kaD6hp0uk=; b=odE0drqXBXPjO8/1nxaQIxcUcnO61BmJoacKjb2TgjXC2Lx15mzxxOr8+7W4vQ2qWnfUA1 cupgNX25HkaHyT1o40fMyQrdSzkMXbWGKprzxTqz7skMyatNAvW07VIiRcpfih/8fJ5UlI BKEB0DEW7sE0GmFq0ol1juYfTt+oJ7Y= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1745258716; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=eVvKIhcDUigy61iYir4MfxXVC274WCrw45kaD6hp0uk=; b=jGWvZEXbad2iULzI22+yZmmxQH2PjAeNfP4fjaDQp3GORjyc6EqU+Ei//kPFs2ggLxNqFl p0UNdtIgdcLMuFgkbzyOIYivmVX1+antMv+gxF8RTqa06ppNFKZLjIrx26N36Ov5cBRjOI eq6IXq52VlzoqiOBjmoVpWBpFsRNUZM= Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-596-weE98q9fN4ySqADSxyhj4A-1; Mon, 21 Apr 2025 14:05:14 -0400 X-MC-Unique: weE98q9fN4ySqADSxyhj4A-1 X-Mimecast-MFC-AGG-ID: weE98q9fN4ySqADSxyhj4A_1745258714 Received: by mail-qt1-f199.google.com with SMTP id d75a77b69052e-478f78ff9beso137671681cf.1 for ; Mon, 21 Apr 2025 11:05:14 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1745258714; x=1745863514; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=eVvKIhcDUigy61iYir4MfxXVC274WCrw45kaD6hp0uk=; b=M/pje7YPKkHtwCLqKBlHYppAWESz3c4TcUQsjJ9fvo3REo0zsN+lCfD3NTqs4gwezS ureQZzcYPT2NQT0uB1pSVRPG9xqgjhB0pKZS8yvJ8UkJH/qiAf1Cp4RjKdtuQHRM+FMN psuuLXPCYMqqubQEnvalJmU2fFxQAA0N3USrWgR5XqOiiplJRDatNOV0F0gTDGiCt5FA JCEJ18FLQbZGqvggqmNK495JSeDuZuEnKK6WijEowRT27mxUHbNmjm7b5zD712L29J6O hsN/sWxXTBFDWb8kif+0E1SrRTvgX8X9AsvSvkL3vkyiHa0VLV+bQITslsFhEsk7h5aw js6A== X-Forwarded-Encrypted: i=1; AJvYcCXgL2sqY8EthyvubVdaq4ECzv0ttGBUm/pUdOpz4UKZj4puHnIYaH1U+tCRhfIAmPAW6yfwTu9LTw==@kvack.org X-Gm-Message-State: AOJu0Yxjq4jcqbLQnLyylAAtbqjrYS3GMWBh/o3m/dikFkhoZUeIfjMp FE/gytN8XYHJTjT5bvQG6Gxywx9KXbFyJB5fCHIBLT6Ovb1B0t8+3XPRnmL0uoE+7/Mxdi2Puqv 4bsA7WSCrwzQ3jaJq4/xOHq8dtUMl+B68XvzOozAurG+JFlBv X-Gm-Gg: ASbGncsEH2ISZUw0lIPwzQKw1Y67CuTmD+WJ9jcU9EmWt9c0Ua+qGCPRI4SPtnjFh4f QMrlIeSmz44og0YSKPfN12CY2xiGFzOXaxZJ41p0rANXY7YVsGXc05rGsh3eLANjm++vpM+5DCx pr+vhAzRtPILhG75N/9O9TwVWJ2paqpSKTmOrlNSedDRKoRVMMszLBfjE3dEZs086lU+6TUTCw6 t7NpzsChQ7ppVkvya6h3x3BaEN3OYJQXc0YpKaQzzNwWcUn8fx3JsNZE7Aqb6Jf2ynFoIx2jOlF 0ThCCPsntJLu3ux8Ink/rcLiye1D13qyckROob6nmMK2qfjFe3T1gg== X-Received: by 2002:a05:622a:130a:b0:476:7e72:3538 with SMTP id d75a77b69052e-47aec4c5b9bmr257980291cf.50.1745258714025; Mon, 21 Apr 2025 11:05:14 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEzSdW6NS+1cQtXXq3zs8Ag1p4QSDq3hHqyATaMXHMXhtpgSTpQ221iJSeiQeHxMsRVOyUsJw== X-Received: by 2002:a05:622a:130a:b0:476:7e72:3538 with SMTP id d75a77b69052e-47aec4c5b9bmr257979471cf.50.1745258713436; Mon, 21 Apr 2025 11:05:13 -0700 (PDT) Received: from athena.aquini.home (c-76-23-219-111.hsd1.me.comcast.net. [76.23.219.111]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-47ae9cfa2ccsm45046821cf.67.2025.04.21.11.05.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Apr 2025 11:05:12 -0700 (PDT) Date: Mon, 21 Apr 2025 14:05:10 -0400 From: Rafael Aquini To: Kees Cook Cc: Petr Mladek , Sergio Perez Gonzalez , Vlastimil Babka , David Rientjes , Bagas Sanjaya , Harry Yoo , Jonathan Corbet , Andrew Morton , Steven Rostedt , Andy Shevchenko , Rasmus Villemoes , Sergey Senozhatsky , Christoph Lameter , Pekka Enberg , Joonsoo Kim , Roman Gushchin , "Paul E. McKenney" , Thomas Huth , "Borislav Petkov (AMD)" , Ard Biesheuvel , Greg Kroah-Hartman , Tamir Duberstein , Alice Ryhl , Stephen Boyd , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v3] slab: Decouple slab_debug and no_hash_pointers Message-ID: References: <20250421165508.make.689-kees@kernel.org> MIME-Version: 1.0 In-Reply-To: <20250421165508.make.689-kees@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 2PZ3_SXIcmu53PDTMckgJQWd2I88qVvaMhbK5S5wwQ4_1745258714 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1D76420014 X-Stat-Signature: enqy5z5ssgga1o99nkuk839ekb97nii7 X-HE-Tag: 1745258716-541245 X-HE-Meta: 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 XPDpk0MT 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 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 Mon, Apr 21, 2025 at 09:55:12AM -0700, 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 > Reviewed-by: Harry Yoo > Acked-by: Rafael Aquini > Tested-by: Petr Mladek > Reviewed-by: Petr Mladek > Signed-off-by: Kees Cook > --- > v3: add docs about implicit "no_hash_pointers" when using "slab_debug" (harry.yoo) > v2: https://lore.kernel.org/all/20250415170232.it.467-kees@kernel.org/ > v1: https://lore.kernel.org/lkml/20250410174428.work.488-kees@kernel.org/ > --- > .../admin-guide/kernel-parameters.txt | 38 ++++++++---- > include/linux/sprintf.h | 2 +- > lib/vsprintf.c | 61 +++++++++++++++++-- > mm/slub.c | 5 +- > 4 files changed, 86 insertions(+), 20 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index d9fd26b95b34..cb12531b2100 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1795,6 +1795,27 @@ > backtraces on all cpus. > Format: 0 | 1 > > + hash_pointers= > + [KNL,EARLY] > + By default, when pointers are printed to the console > + or buffers via the %p format string, that pointer is > + "hashed", i.e. obscured by hashing the pointer value. > + This is a security feature that hides actual kernel > + addresses from unprivileged users, but it also makes > + debugging the kernel more difficult since unequal > + pointers can no longer be compared. The choices are: > + Format: { auto | always | never } > + Default: auto > + > + auto - Hash pointers unless slab_debug is enabled. > + always - Always hash pointers (even if slab_debug is > + enabled). > + never - Never hash pointers. This option should only > + be specified when debugging the kernel. Do > + not use on production kernels. The boot > + param "no_hash_pointers" is an alias for > + this mode. > + > hashdist= [KNL,NUMA] Large hashes allocated during boot > are distributed across NUMA nodes. Defaults on > for 64-bit NUMA, off otherwise. > @@ -4117,18 +4138,7 @@ > > no_hash_pointers > [KNL,EARLY] > - Force pointers printed to the console or buffers to be > - unhashed. By default, when a pointer is printed via %p > - format string, that pointer is "hashed", i.e. obscured > - by hashing the pointer value. This is a security feature > - that hides actual kernel addresses from unprivileged > - users, but it also makes debugging the kernel more > - difficult since unequal pointers can no longer be > - compared. However, if this command-line option is > - specified, then all normal pointers will have their true > - value printed. This option should only be specified when > - debugging the kernel. Please do not use on production > - kernels. > + Alias for "hash_pointers=never". > > nohibernate [HIBERNATION] Disable hibernation and resume. > > @@ -6478,6 +6488,10 @@ > Documentation/mm/slub.rst. > (slub_debug legacy name also accepted for now) > > + Using this option implies the "no_hash_pointers" > + option which can be undone by adding the > + "hash_pointers=always" option. > + > slab_max_order= [MM] > Determines the maximum allowed order for slabs. > A high setting may cause OOMs due to memory > diff --git a/include/linux/sprintf.h b/include/linux/sprintf.h > index 51cab2def9ec..521bb2cd2648 100644 > --- a/include/linux/sprintf.h > +++ b/include/linux/sprintf.h > @@ -22,7 +22,7 @@ __scanf(2, 0) int vsscanf(const char *, const char *, va_list); > > /* These are for specific cases, do not use without real need */ > extern bool no_hash_pointers; > -int no_hash_pointers_enable(char *str); > +void hash_pointers_finalize(bool slub_debug); > > /* Used for Rust formatting ('%pA') */ > char *rust_fmt_argument(char *buf, char *end, const void *ptr); > 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); > > /* > diff --git a/mm/slub.c b/mm/slub.c > index b46f87662e71..f3d61b330a76 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6314,9 +6314,8 @@ 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); > + /* Inform pointer hashing choice about slub debugging state. */ > + hash_pointers_finalize(__slub_debug_enabled()); > > kmem_cache_node = &boot_kmem_cache_node; > kmem_cache = &boot_kmem_cache; > -- > 2.34.1 > > Acked-by: Rafael Aquini