From patchwork Wed Oct 18 04:21:55 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tobin Harding X-Patchwork-Id: 10013431 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id E7F74602C8 for ; Wed, 18 Oct 2017 04:22:21 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CE516289AC for ; Wed, 18 Oct 2017 04:22:21 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C198328A9C; Wed, 18 Oct 2017 04:22:21 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 6B2FB289AC for ; Wed, 18 Oct 2017 04:22:19 +0000 (UTC) Received: (qmail 25941 invoked by uid 550); 18 Oct 2017 04:22:18 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 25923 invoked from network); 18 Oct 2017 04:22:17 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tobin.cc; h=cc :date:from:message-id:subject:to:x-me-sender:x-me-sender :x-sasl-enc; s=fm1; bh=GumaPoxT3CQJU0XYT02eJI+NDBNzBoce3ILTVtz5z WQ=; b=mbsM+8qVcGPFtPl02a022o53DRo6AeUIfQOAj8nGOV7F5fmXsCsoCsQrj oalnnTYjnXbkSjZR5RJbaETmdZQ1bcF2CPZWsP9Z+9fshGakSGe4FK813xGcgCbj mSER8W1z9dsONK50353+g9fFfP2pa2r6Hvw06OWHWdNRxCCv2sRA3703e7v2ibPY AXcRsl4JLlQzjYZN/lG1tB1miU2Ovb9pxCPTHAgOxG5kvrrDkdS8lu0OP7dhT4p5 wFEaak/UIn1Op3W9kYVdCsB+FoV5Tki2vdYO/ZW+KYvPAfldWufLw0yCqVp42luK Ob5n0tEsZXv/8yqZaH5Ls7V202L8g== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:date:from:message-id:subject:to :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; bh=GumaPoxT3CQJU0XYT 02eJI+NDBNzBoce3ILTVtz5zWQ=; b=b3YwMZ0VxkbHO0kWQC0J4Hzpr0nH+JA98 mponC4S+wCD3TukWWPQOvbkMcayErD7DcQjnUOkmBsqJv8alGS8dXbIHWZOdskBC bB0dkG7mxwCEvHtOO+QvmMf48YayPiztZtoR/XFXr5IufKZpsK4IJbXZX4sxX73g 6Uq0sGfWBE1Xbj/P5hRaDiJm92Ha90XU3EK+1z0xipnHUyYLoLwZd5dsmMDnqYis Q4f+qsp5nRko1KfoNrfM1CaDrVLdjmyKq6AcxUDNu5y5Hk/pO0Knxrou88Op19rG fQZjefe1FHxl2+5YD/8CUkpr6cjJe1RP9Q5xiFuHPVd2lqzWdIXjA== X-ME-Sender: From: "Tobin C. Harding" To: kernel-hardening@lists.openwall.com Cc: "Tobin C. Harding" , Linus Torvalds , Kees Cook , Paolo Bonzini , Tycho Andersen , "Roberts, William C" , Tejun Heo , Jordan Glover , Greg KH , Petr Mladek , Joe Perches , Ian Campbell , Sergey Senozhatsky , Catalin Marinas , Will Deacon , Steven Rostedt , Chris Fries , Dave Weinstein , Daniel Micay , Djalal Harouni , linux-kernel@vger.kernel.org Date: Wed, 18 Oct 2017 15:21:55 +1100 Message-Id: <1508300515-28824-1-git-send-email-me@tobin.cc> X-Mailer: git-send-email 2.7.4 Subject: [kernel-hardening] [PATCH v4] printk: hash addresses printed with %p X-Virus-Scanned: ClamAV using ClamSMTP Currently there are many places in the kernel where addresses are being printed using an unadorned %p. Kernel pointers should be printed using %pK allowing some control via the kptr_restrict sysctl. Exposing addresses gives attackers sensitive information about the kernel layout in memory. We can reduce the attack surface by hashing all addresses printed with %p. This will of course break some users, forcing code printing needed addresses to be updated. For what it's worth, usage of unadorned %p can be broken down as follows (thanks to Joe Perches). $ git grep -E '%p[^A-Za-z0-9]' | cut -f1 -d"/" | sort | uniq -c 1084 arch 20 block 10 crypto 32 Documentation 8121 drivers 1221 fs 143 include 101 kernel 69 lib 100 mm 1510 net 40 samples 7 scripts 11 security 166 sound 152 tools 2 virt Add function ptr_to_id() to map an address to a 32 bit unique identifier. Signed-off-by: Tobin C. Harding --- V4: - Remove changes to siphash.{ch} - Do word size check, and return value cast, directly in ptr_to_id(). - Use add_ready_random_callback() to guard call to get_random_bytes() V3: - Use atomic_xchg() to guard setting [random] key. - Remove erroneous white space change. V2: - Use SipHash to do the hashing. The discussion related to this patch has been fragmented. There are three threads associated with this patch. Email threads by subject: [PATCH] printk: hash addresses printed with %p [PATCH 0/3] add %pX specifier [kernel-hardening] [RFC V2 0/6] add more kernel pointer filter options lib/vsprintf.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 71 insertions(+), 3 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 86c3385b9eb3..4609738cd2cd 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -33,6 +33,8 @@ #include #include #include +#include +#include #ifdef CONFIG_BLOCK #include #endif @@ -1591,6 +1593,70 @@ char *device_node_string(char *buf, char *end, struct device_node *dn, return widen_string(buf, buf - buf_start, end, spec); } +/* protects ptr_secret and have_key */ +DEFINE_SPINLOCK(key_lock); +static siphash_key_t ptr_secret __read_mostly; +static atomic_t have_key = ATOMIC_INIT(0); + +static int initialize_ptr_secret(void) +{ + spin_lock(&key_lock); + if (atomic_read(&have_key) == 1) + goto unlock; + + get_random_bytes(&ptr_secret, sizeof(ptr_secret)); + atomic_set(&have_key, 1); + +unlock: + spin_unlock(&key_lock); + return 0; +} + +static void schedule_async_key_init(struct random_ready_callback *rdy) +{ + initialize_ptr_secret(); +} + +/* Maps a pointer to a 32 bit unique identifier. */ +static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec) +{ + static struct random_ready_callback random_ready; + unsigned int hashval; + int err; + + if (atomic_read(&have_key) == 0) { + random_ready.owner = NULL; + random_ready.func = schedule_async_key_init; + + err = add_random_ready_callback(&random_ready); + + switch (err) { + case 0: + return "(pointer value)"; + + case -EALREADY: + initialize_ptr_secret(); + break; + + default: + /* shouldn't get here */ + return "(ptr_to_id() error)"; + } + } + +#ifdef CONFIG_64BIT + hashval = (unsigned int)siphash_1u64((u64)ptr, &ptr_secret); +#else + hashval = (unsigned int)siphash_1u32((u32)ptr, &ptr_secret); +#endif + + spec.field_width = 2 + 2 * sizeof(unsigned int); /* 0x + hex */ + spec.flags = SPECIAL | SMALL | ZEROPAD; + spec.base = 16; + + return number(buf, end, hashval, spec); +} + int kptr_restrict __read_mostly; /* @@ -1703,6 +1769,9 @@ int kptr_restrict __read_mostly; * Note: The difference between 'S' and 'F' is that on ia64 and ppc64 * function pointers are really function descriptors, which contain a * pointer to the real address. + * + * Default behaviour (unadorned %p) is to hash the address, rendering it useful + * as a unique identifier. */ static noinline_for_stack char *pointer(const char *fmt, char *buf, char *end, void *ptr, @@ -1858,14 +1927,13 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, return device_node_string(buf, end, ptr, spec, fmt + 1); } } - spec.flags |= SMALL; + if (spec.field_width == -1) { spec.field_width = default_width; spec.flags |= ZEROPAD; } - spec.base = 16; - return number(buf, end, (unsigned long) ptr, spec); + return ptr_to_id(buf, end, ptr, spec); } /*