linux-kernel - [PATCH 3.18 24/45] drivers: char: random: add get_random

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Message-Id: <20170612152554.665958513@linuxfoundation.org>
Date:   Mon, 12 Jun 2017 17:26:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Daniel Cashman <dcashman@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        "Theodore Tso" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Nick Kralevich <nnk@...gle.com>,
        Jeff Vander Stoep <jeffv@...gle.com>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.18 24/45] drivers: char: random: add get_random_long()

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Cashman <dcashman@...roid.com>

commit ec9ee4acd97c0039a61c0ae4f12705767ae62153 upstream.

Commit d07e22597d1d ("mm: mmap: add new /proc tunable for mmap_base
ASLR") added the ability to choose from a range of values to use for
entropy count in generating the random offset to the mmap_base address.

The maximum value on this range was set to 32 bits for 64-bit x86
systems, but this value could be increased further, requiring more than
the 32 bits of randomness provided by get_random_int(), as is already
possible for arm64.  Add a new function: get_random_long() which more
naturally fits with the mmap usage of get_random_int() but operates
exactly the same as get_random_int().

Also, fix the shifting constant in mmap_rnd() to be an unsigned long so
that values greater than 31 bits generate an appropriate mask without
overflow.  This is especially important on x86, as its shift instruction
uses a 5-bit mask for the shift operand, which meant that any value for
mmap_rnd_bits over 31 acts as a no-op and effectively disables mmap_base
randomization.

Finally, replace calls to get_random_int() with get_random_long() where
appropriate.

This patch (of 2):

Add get_random_long().

Signed-off-by: Daniel Cashman <dcashman@...roid.com>
Acked-by: Kees Cook <keescook@...omium.org>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: David S. Miller <davem@...emloft.net>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Nick Kralevich <nnk@...gle.com>
Cc: Jeff Vander Stoep <jeffv@...gle.com>
Cc: Mark Salyzyn <salyzyn@...roid.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/char/random.c  |   22 ++++++++++++++++++++++
 include/linux/random.h |    1 +
 2 files changed, 23 insertions(+)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1741,6 +1741,28 @@ unsigned int get_random_int(void)
 EXPORT_SYMBOL(get_random_int);

 /*
+ * Same as get_random_int(), but returns unsigned long.
+ */
+unsigned long get_random_long(void)
+{
+	__u32 *hash;
+	unsigned long ret;
+
+	if (arch_get_random_long(&ret))
+		return ret;
+
+	hash = get_cpu_var(get_random_int_hash);
+
+	hash[0] += current->pid + jiffies + random_get_entropy();
+	md5_transform(hash, random_int_secret);
+	ret = *(unsigned long *)hash;
+	put_cpu_var(get_random_int_hash);
+
+	return ret;
+}
+EXPORT_SYMBOL(get_random_long);
+
+/*
  * randomize_range() returns a start address such that
  *
  *    [...... <range> .....]
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -23,6 +23,7 @@ extern const struct file_operations rand
 #endif

 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);

 u32 prandom_u32(void);