From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763513AbdJQR1r convert rfc822-to-8bit (ORCPT ); Tue, 17 Oct 2017 13:27:47 -0400 Received: from mga14.intel.com ([192.55.52.115]:35611 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755276AbdJQR1p (ORCPT ); Tue, 17 Oct 2017 13:27:45 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.43,391,1503385200"; d="scan'208";a="1231824847" From: "Roberts, William C" To: "Tobin C. Harding" , "kernel-hardening@lists.openwall.com" CC: Linus Torvalds , Kees Cook , Paolo Bonzini , Tycho Andersen , 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" Subject: RE: [PATCH v2] printk: hash addresses printed with %p Thread-Topic: [PATCH v2] printk: hash addresses printed with %p Thread-Index: AQHTRwPkQmA8Krxrt0GGOGI/dyO6k6LoSuKQ Date: Tue, 17 Oct 2017 17:27:15 +0000 Message-ID: <476DC76E7D1DF2438D32BFADF679FC563F4B0FB8@ORSMSX115.amr.corp.intel.com> References: <1508215972-7769-1-git-send-email-me@tobin.cc> In-Reply-To: <1508215972-7769-1-git-send-email-me@tobin.cc> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-product: dlpe-windows dlp-version: 11.0.0.116 dlp-reaction: no-action x-originating-ip: [10.22.254.139] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Tobin C. Harding [mailto:me@tobin.cc] > Sent: Monday, October 16, 2017 9:53 PM > To: kernel-hardening@lists.openwall.com > Cc: Tobin C. Harding ; Linus Torvalds foundation.org>; 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 > Subject: [PATCH v2] printk: hash addresses printed with %p > > 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 > > git grep '%p[^KFfSsBRrbMmIiEUVKNhdDgCGO]' | wc -l > > arch: 2512 > block: 20 > crypto: 12 > fs: 1221 > include: 147 > kernel: 109 > lib: 77 > mm: 120 > net: 1516 > security: 11 > sound: 168 > virt: 2 > drivers: 8420 > > Add helper function siphash_1ulong(). Add function ptr_to_id() to map an > address to a 32 bit unique identifier. > > Signed-off-by: Tobin C. Harding > --- > > V2: > - Use SipHash to do the hashing > > The discussion related to this patch has been fragmented. There are three other > 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 > > include/linux/siphash.h | 2 ++ > lib/siphash.c | 13 +++++++++++++ > lib/vsprintf.c | 32 +++++++++++++++++++++++++++++--- > 3 files changed, 44 insertions(+), 3 deletions(-) > > diff --git a/include/linux/siphash.h b/include/linux/siphash.h index > fa7a6b9cedbf..a9392568c8b8 100644 > --- a/include/linux/siphash.h > +++ b/include/linux/siphash.h > @@ -26,6 +26,8 @@ u64 __siphash_aligned(const void *data, size_t len, const > siphash_key_t *key); > u64 __siphash_unaligned(const void *data, size_t len, const siphash_key_t > *key); #endif > > +unsigned long siphash_1ulong(const unsigned long a, const siphash_key_t > +*key); > + > u64 siphash_1u64(const u64 a, const siphash_key_t *key); > u64 siphash_2u64(const u64 a, const u64 b, const siphash_key_t *key); > u64 siphash_3u64(const u64 a, const u64 b, const u64 c, diff --git a/lib/siphash.c > b/lib/siphash.c index 3ae58b4edad6..63f4ff57c9ce 100644 > --- a/lib/siphash.c > +++ b/lib/siphash.c > @@ -116,6 +116,19 @@ EXPORT_SYMBOL(__siphash_unaligned); > #endif > > /** > + * siphash_1ulong - computes siphash PRF value > + * @first: value to hash > + * @key: the siphash key > + */ > +unsigned long siphash_1ulong(const unsigned long first, const > +siphash_key_t *key) { #ifdef CONFIG_64BIT > + return (unsigned long)siphash_1u64((u64)first, key); #endif > + return (unsigned long)siphash_1u32((u32)first, key); } > + > +/** > * siphash_1u64 - compute 64-bit siphash PRF value of a u64 > * @first: first u64 > * @key: the siphash key > diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 86c3385b9eb3..afd1c835b0f6 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -33,6 +33,7 @@ > #include > #include > #include > +#include > #ifdef CONFIG_BLOCK > #include > #endif > @@ -503,6 +504,7 @@ char *number(char *buf, char *end, unsigned long long > num, > *buf = '0'; > ++buf; > } > + Unneeded whitespace change? > /* actual digits of result */ > while (--i >= 0) { > if (buf < end) > @@ -1591,6 +1593,28 @@ char *device_node_string(char *buf, char *end, struct > device_node *dn, > return widen_string(buf, buf - buf_start, end, spec); } > > +/* 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 siphash_key_t ptr_secret __read_mostly; > + static bool have_key = false; > + unsigned long hashval; > + > + /* Kernel doesn't boot if we use get_random_once() */ > + if (!have_key) { > + get_random_bytes(&ptr_secret, sizeof(ptr_secret)); > + have_key = true; Wouldn't one want to use an atomic test and swap for this block? > + } > + > + hashval = siphash_1ulong((unsigned long)ptr, &ptr_secret); > + > + spec.field_width = 2 + 2 * sizeof(unsigned int); /* 0x + hex */ > + spec.flags = SPECIAL | SMALL | ZEROPAD; > + spec.base = 16; > + > + return number(buf, end, (u32)hashval, spec); } > + > int kptr_restrict __read_mostly; > > /* > @@ -1703,6 +1727,9 @@ 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 > +1885,13 @@ 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); > } > > /* > -- > 2.7.4