From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753948AbcGaQq7 (ORCPT ); Sun, 31 Jul 2016 12:46:59 -0400 Received: from mail-wm0-f51.google.com ([74.125.82.51]:35393 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753324AbcGaQq4 (ORCPT ); Sun, 31 Jul 2016 12:46:56 -0400 MIME-Version: 1.0 In-Reply-To: <20160730154244.403-2-jason@lakedaemon.net> References: <20160728204730.27453-1-jason@lakedaemon.net> <20160730154244.403-1-jason@lakedaemon.net> <20160730154244.403-2-jason@lakedaemon.net> From: Kees Cook Date: Sun, 31 Jul 2016 09:46:53 -0700 X-Google-Sender-Auth: HNMznQPBogJCyLhitxw0nWsNHYM Message-ID: Subject: Re: [PATCH v2 1/7] random: Simplify API for random address requests To: Jason Cooper Cc: "Roberts, William C" , Yann Droneaud , Linux-MM , LKML , "kernel-hardening@lists.openwall.com" , Russell King - ARM Linux , Andrew Morton , "Theodore Ts'o" , Arnd Bergmann , Greg KH , Catalin Marinas , Will Deacon , Ralf Baechle , "benh@kernel.crashing.org" , Paul Mackerras , Michael Ellerman , "David S. Miller" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , Al Viro , Nick Kralevich , Jeffrey Vander Stoep , Daniel Cashman Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jul 30, 2016 at 8:42 AM, Jason Cooper wrote: > To date, all callers of randomize_range() have set the length to 0, and > check for a zero return value. For the current callers, the only way > to get zero returned is if end <= start. Since they are all adding a > constant to the start address, this is unnecessary. > > We can remove a bunch of needless checks by simplifying the API to do > just what everyone wants, return an address between [start, start + > range). > > While we're here, s/get_random_int/get_random_long/. No current call > site is adversely affected by get_random_int(), since all current range > requests are < UINT_MAX. However, we should match caller expectations > to avoid coming up short (ha!) in the future. > > All current callers to randomize_range() chose to use the start address > if randomize_range() failed. Therefore, we simplify things by just > returning the start address on error. > > randomize_range() will be removed once all callers have been converted > over to randomize_addr(). > > Signed-off-by: Jason Cooper > --- > Changes from v1: > - Explicitly mention page_aligned start assumption (Yann Droneaud) > - pick random pages vice random addresses (Yann Droneaud) > - catch range=0 last > > drivers/char/random.c | 28 ++++++++++++++++++++++++++++ > include/linux/random.h | 1 + > 2 files changed, 29 insertions(+) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 0158d3bff7e5..3bedf69546d6 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1840,6 +1840,34 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len) > return PAGE_ALIGN(get_random_int() % range + start); > } > > +/** > + * randomize_addr - Generate a random, page aligned address > + * @start: The smallest acceptable address the caller will take. > + * @range: The size of the area, starting at @start, within which the > + * random address must fall. > + * > + * If @start + @range would overflow, @range is capped. > + * > + * NOTE: Historical use of randomize_range, which this replaces, presumed that > + * @start was already page aligned. This assumption still holds. > + * > + * Return: A page aligned address within [start, start + range). On error, > + * @start is returned. > + */ > +unsigned long > +randomize_addr(unsigned long start, unsigned long range) Since we're changing other things about this, let's try to document its behavior in its name too and call this "randomize_page" instead. If it requires a page-aligned value, we should probably also BUG_ON it, or adjust the start too. -Kees > +{ > + if (start > ULONG_MAX - range) > + range = ULONG_MAX - start; > + > + range >>= PAGE_SHIFT; > + > + if (range == 0) > + return start; > + > + return start + (get_random_long() % range << PAGE_SHIFT); > +} > + > /* Interface for in-kernel drivers of true hardware RNGs. > * Those devices may produce endless random bits and will be throttled > * when our pool is full. > diff --git a/include/linux/random.h b/include/linux/random.h > index e47e533742b5..f1ca2fa4c071 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -35,6 +35,7 @@ extern const struct file_operations random_fops, urandom_fops; > unsigned int get_random_int(void); > unsigned long get_random_long(void); > unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len); > +unsigned long randomize_addr(unsigned long start, unsigned long range); > > u32 prandom_u32(void); > void prandom_bytes(void *buf, size_t nbytes); > -- > 2.9.2 > -- Kees Cook Chrome OS & Brillo Security From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 437946B0273 for ; Sun, 31 Jul 2016 12:46:56 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id p129so67738730wmp.3 for ; Sun, 31 Jul 2016 09:46:56 -0700 (PDT) Received: from mail-wm0-x22b.google.com (mail-wm0-x22b.google.com. [2a00:1450:400c:c09::22b]) by mx.google.com with ESMTPS id f10si12343885wme.70.2016.07.31.09.46.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 31 Jul 2016 09:46:54 -0700 (PDT) Received: by mail-wm0-x22b.google.com with SMTP id q128so343660938wma.1 for ; Sun, 31 Jul 2016 09:46:54 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160730154244.403-2-jason@lakedaemon.net> References: <20160728204730.27453-1-jason@lakedaemon.net> <20160730154244.403-1-jason@lakedaemon.net> <20160730154244.403-2-jason@lakedaemon.net> From: Kees Cook Date: Sun, 31 Jul 2016 09:46:53 -0700 Message-ID: Subject: Re: [PATCH v2 1/7] random: Simplify API for random address requests Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Jason Cooper Cc: "Roberts, William C" , Yann Droneaud , Linux-MM , LKML , "kernel-hardening@lists.openwall.com" , Russell King - ARM Linux , Andrew Morton , Theodore Ts'o , Arnd Bergmann , Greg KH , Catalin Marinas , Will Deacon , Ralf Baechle , "benh@kernel.crashing.org" , Paul Mackerras , Michael Ellerman , "David S. Miller" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , Al Viro , Nick Kralevich , Jeffrey Vander Stoep , Daniel Cashman On Sat, Jul 30, 2016 at 8:42 AM, Jason Cooper wrote: > To date, all callers of randomize_range() have set the length to 0, and > check for a zero return value. For the current callers, the only way > to get zero returned is if end <= start. Since they are all adding a > constant to the start address, this is unnecessary. > > We can remove a bunch of needless checks by simplifying the API to do > just what everyone wants, return an address between [start, start + > range). > > While we're here, s/get_random_int/get_random_long/. No current call > site is adversely affected by get_random_int(), since all current range > requests are < UINT_MAX. However, we should match caller expectations > to avoid coming up short (ha!) in the future. > > All current callers to randomize_range() chose to use the start address > if randomize_range() failed. Therefore, we simplify things by just > returning the start address on error. > > randomize_range() will be removed once all callers have been converted > over to randomize_addr(). > > Signed-off-by: Jason Cooper > --- > Changes from v1: > - Explicitly mention page_aligned start assumption (Yann Droneaud) > - pick random pages vice random addresses (Yann Droneaud) > - catch range=0 last > > drivers/char/random.c | 28 ++++++++++++++++++++++++++++ > include/linux/random.h | 1 + > 2 files changed, 29 insertions(+) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 0158d3bff7e5..3bedf69546d6 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1840,6 +1840,34 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len) > return PAGE_ALIGN(get_random_int() % range + start); > } > > +/** > + * randomize_addr - Generate a random, page aligned address > + * @start: The smallest acceptable address the caller will take. > + * @range: The size of the area, starting at @start, within which the > + * random address must fall. > + * > + * If @start + @range would overflow, @range is capped. > + * > + * NOTE: Historical use of randomize_range, which this replaces, presumed that > + * @start was already page aligned. This assumption still holds. > + * > + * Return: A page aligned address within [start, start + range). On error, > + * @start is returned. > + */ > +unsigned long > +randomize_addr(unsigned long start, unsigned long range) Since we're changing other things about this, let's try to document its behavior in its name too and call this "randomize_page" instead. If it requires a page-aligned value, we should probably also BUG_ON it, or adjust the start too. -Kees > +{ > + if (start > ULONG_MAX - range) > + range = ULONG_MAX - start; > + > + range >>= PAGE_SHIFT; > + > + if (range == 0) > + return start; > + > + return start + (get_random_long() % range << PAGE_SHIFT); > +} > + > /* Interface for in-kernel drivers of true hardware RNGs. > * Those devices may produce endless random bits and will be throttled > * when our pool is full. > diff --git a/include/linux/random.h b/include/linux/random.h > index e47e533742b5..f1ca2fa4c071 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -35,6 +35,7 @@ extern const struct file_operations random_fops, urandom_fops; > unsigned int get_random_int(void); > unsigned long get_random_long(void); > unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len); > +unsigned long randomize_addr(unsigned long start, unsigned long range); > > u32 prandom_u32(void); > void prandom_bytes(void *buf, size_t nbytes); > -- > 2.9.2 > -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com MIME-Version: 1.0 Sender: keescook@google.com In-Reply-To: <20160730154244.403-2-jason@lakedaemon.net> References: <20160728204730.27453-1-jason@lakedaemon.net> <20160730154244.403-1-jason@lakedaemon.net> <20160730154244.403-2-jason@lakedaemon.net> From: Kees Cook Date: Sun, 31 Jul 2016 09:46:53 -0700 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: [kernel-hardening] Re: [PATCH v2 1/7] random: Simplify API for random address requests To: Jason Cooper Cc: "Roberts, William C" , Yann Droneaud , Linux-MM , LKML , "kernel-hardening@lists.openwall.com" , Russell King - ARM Linux , Andrew Morton , Theodore Ts'o , Arnd Bergmann , Greg KH , Catalin Marinas , Will Deacon , Ralf Baechle , "benh@kernel.crashing.org" , Paul Mackerras , Michael Ellerman , "David S. Miller" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , Al Viro , Nick Kralevich , Jeffrey Vander Stoep , Daniel Cashman List-ID: On Sat, Jul 30, 2016 at 8:42 AM, Jason Cooper wrote: > To date, all callers of randomize_range() have set the length to 0, and > check for a zero return value. For the current callers, the only way > to get zero returned is if end <= start. Since they are all adding a > constant to the start address, this is unnecessary. > > We can remove a bunch of needless checks by simplifying the API to do > just what everyone wants, return an address between [start, start + > range). > > While we're here, s/get_random_int/get_random_long/. No current call > site is adversely affected by get_random_int(), since all current range > requests are < UINT_MAX. However, we should match caller expectations > to avoid coming up short (ha!) in the future. > > All current callers to randomize_range() chose to use the start address > if randomize_range() failed. Therefore, we simplify things by just > returning the start address on error. > > randomize_range() will be removed once all callers have been converted > over to randomize_addr(). > > Signed-off-by: Jason Cooper > --- > Changes from v1: > - Explicitly mention page_aligned start assumption (Yann Droneaud) > - pick random pages vice random addresses (Yann Droneaud) > - catch range=0 last > > drivers/char/random.c | 28 ++++++++++++++++++++++++++++ > include/linux/random.h | 1 + > 2 files changed, 29 insertions(+) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 0158d3bff7e5..3bedf69546d6 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1840,6 +1840,34 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len) > return PAGE_ALIGN(get_random_int() % range + start); > } > > +/** > + * randomize_addr - Generate a random, page aligned address > + * @start: The smallest acceptable address the caller will take. > + * @range: The size of the area, starting at @start, within which the > + * random address must fall. > + * > + * If @start + @range would overflow, @range is capped. > + * > + * NOTE: Historical use of randomize_range, which this replaces, presumed that > + * @start was already page aligned. This assumption still holds. > + * > + * Return: A page aligned address within [start, start + range). On error, > + * @start is returned. > + */ > +unsigned long > +randomize_addr(unsigned long start, unsigned long range) Since we're changing other things about this, let's try to document its behavior in its name too and call this "randomize_page" instead. If it requires a page-aligned value, we should probably also BUG_ON it, or adjust the start too. -Kees > +{ > + if (start > ULONG_MAX - range) > + range = ULONG_MAX - start; > + > + range >>= PAGE_SHIFT; > + > + if (range == 0) > + return start; > + > + return start + (get_random_long() % range << PAGE_SHIFT); > +} > + > /* Interface for in-kernel drivers of true hardware RNGs. > * Those devices may produce endless random bits and will be throttled > * when our pool is full. > diff --git a/include/linux/random.h b/include/linux/random.h > index e47e533742b5..f1ca2fa4c071 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -35,6 +35,7 @@ extern const struct file_operations random_fops, urandom_fops; > unsigned int get_random_int(void); > unsigned long get_random_long(void); > unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len); > +unsigned long randomize_addr(unsigned long start, unsigned long range); > > u32 prandom_u32(void); > void prandom_bytes(void *buf, size_t nbytes); > -- > 2.9.2 > -- Kees Cook Chrome OS & Brillo Security