linux-kernel - [tip:x86/urgent] x86, mm/ASLR: Fix stack randomization on 64-bit systems

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <tip-4e7c22d447bb6d7e37bfe39ff658486ae78e8d77@git.kernel.org>
Date:	Thu, 19 Feb 2015 11:27:56 -0800
From:	tip-bot for Hector Marco-Gisbert <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	akpm@...ux-foundation.org, bp@...e.de,
	linux-kernel@...r.kernel.org, hpa@...or.com, keescook@...omium.org,
	viro@...iv.linux.org.uk, mingo@...nel.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de, hecmargi@....es,
	iripoll@....es, stable@...r.kernel.org
Subject: [tip:x86/urgent] x86, mm/ASLR:
  Fix stack randomization on 64-bit systems

Commit-ID:  4e7c22d447bb6d7e37bfe39ff658486ae78e8d77
Gitweb:     http://git.kernel.org/tip/4e7c22d447bb6d7e37bfe39ff658486ae78e8d77
Author:     Hector Marco-Gisbert <hecmargi@....es>
AuthorDate: Sat, 14 Feb 2015 09:33:50 -0800
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Thu, 19 Feb 2015 12:21:36 +0100

x86, mm/ASLR: Fix stack randomization on 64-bit systems

The issue is that the stack for processes is not properly randomized on
64 bit architectures due to an integer overflow.

The affected function is randomize_stack_top() in file
"fs/binfmt_elf.c":

  static unsigned long randomize_stack_top(unsigned long stack_top)
  {
           unsigned int random_variable = 0;

           if ((current->flags & PF_RANDOMIZE) &&
                   !(current->personality & ADDR_NO_RANDOMIZE)) {
                   random_variable = get_random_int() & STACK_RND_MASK;
                   random_variable <<= PAGE_SHIFT;
           }
           return PAGE_ALIGN(stack_top) + random_variable;
           return PAGE_ALIGN(stack_top) - random_variable;
  }

Note that, it declares the "random_variable" variable as "unsigned int".
Since the result of the shifting operation between STACK_RND_MASK (which
is 0x3fffff on x86_64, 22 bits) and PAGE_SHIFT (which is 12 on x86_64):

	  random_variable <<= PAGE_SHIFT;

then the two leftmost bits are dropped when storing the result in the
"random_variable". This variable shall be at least 34 bits long to hold
the (22+12) result.

These two dropped bits have an impact on the entropy of process stack.
Concretely, the total stack entropy is reduced by four: from 2^28 to
2^30 (One fourth of expected entropy).

This patch restores back the entropy by correcting the types involved
in the operations in the functions randomize_stack_top() and
stack_maxrandom_size().

The successful fix can be tested with:

  $ for i in `seq 1 10`; do cat /proc/self/maps | grep stack; done
  7ffeda566000-7ffeda587000 rw-p 00000000 00:00 0                          [stack]
  7fff5a332000-7fff5a353000 rw-p 00000000 00:00 0                          [stack]
  7ffcdb7a1000-7ffcdb7c2000 rw-p 00000000 00:00 0                          [stack]
  7ffd5e2c4000-7ffd5e2e5000 rw-p 00000000 00:00 0                          [stack]
  ...

Once corrected, the leading bytes should be between 7ffc and 7fff,
rather than always being 7fff.

Signed-off-by: Hector Marco-Gisbert <hecmargi@....es>
Signed-off-by: Ismael Ripoll <iripoll@....es>
[ Rebased, fixed 80 char bugs, cleaned up commit message, added test example and CVE ]
Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: <stable@...r.kernel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Fixes: CVE-2015-1593
Link: http://lkml.kernel.org/r/20150214173350.GA18393@www.outflux.net
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/mm/mmap.c | 6 +++---
 fs/binfmt_elf.c    | 5 +++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 919b912..df4552b 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -35,12 +35,12 @@ struct va_alignment __read_mostly va_align = {
 	.flags = -1,
 };
 
-static unsigned int stack_maxrandom_size(void)
+static unsigned long stack_maxrandom_size(void)
 {
-	unsigned int max = 0;
+	unsigned long max = 0;
 	if ((current->flags & PF_RANDOMIZE) &&
 		!(current->personality & ADDR_NO_RANDOMIZE)) {
-		max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
+		max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
 	}
 
 	return max;
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 02b1691..995986b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -645,11 +645,12 @@ out:
 
 static unsigned long randomize_stack_top(unsigned long stack_top)
 {
-	unsigned int random_variable = 0;
+	unsigned long random_variable = 0;
 
 	if ((current->flags & PF_RANDOMIZE) &&
 		!(current->personality & ADDR_NO_RANDOMIZE)) {
-		random_variable = get_random_int() & STACK_RND_MASK;
+		random_variable = (unsigned long) get_random_int();
+		random_variable &= STACK_RND_MASK;
 		random_variable <<= PAGE_SHIFT;
 	}
 #ifdef CONFIG_STACK_GROWSUP
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/