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113 lines
4.0 KiB
Diff
113 lines
4.0 KiB
Diff
From 4e7c22d447bb6d7e37bfe39ff658486ae78e8d77 Mon Sep 17 00:00:00 2001
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From: Hector Marco-Gisbert <hecmargi@upv.es>
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Date: Sat, 14 Feb 2015 09:33:50 -0800
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Subject: x86, mm/ASLR: Fix stack randomization on 64-bit systems
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The issue is that the stack for processes is not properly randomized on
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64 bit architectures due to an integer overflow.
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The affected function is randomize_stack_top() in file
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"fs/binfmt_elf.c":
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static unsigned long randomize_stack_top(unsigned long stack_top)
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{
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unsigned int random_variable = 0;
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if ((current->flags & PF_RANDOMIZE) &&
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!(current->personality & ADDR_NO_RANDOMIZE)) {
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random_variable = get_random_int() & STACK_RND_MASK;
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random_variable <<= PAGE_SHIFT;
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}
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return PAGE_ALIGN(stack_top) + random_variable;
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return PAGE_ALIGN(stack_top) - random_variable;
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}
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Note that, it declares the "random_variable" variable as "unsigned int".
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Since the result of the shifting operation between STACK_RND_MASK (which
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is 0x3fffff on x86_64, 22 bits) and PAGE_SHIFT (which is 12 on x86_64):
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random_variable <<= PAGE_SHIFT;
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then the two leftmost bits are dropped when storing the result in the
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"random_variable". This variable shall be at least 34 bits long to hold
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the (22+12) result.
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These two dropped bits have an impact on the entropy of process stack.
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Concretely, the total stack entropy is reduced by four: from 2^28 to
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2^30 (One fourth of expected entropy).
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This patch restores back the entropy by correcting the types involved
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in the operations in the functions randomize_stack_top() and
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stack_maxrandom_size().
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The successful fix can be tested with:
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$ for i in `seq 1 10`; do cat /proc/self/maps | grep stack; done
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7ffeda566000-7ffeda587000 rw-p 00000000 00:00 0 [stack]
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7fff5a332000-7fff5a353000 rw-p 00000000 00:00 0 [stack]
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7ffcdb7a1000-7ffcdb7c2000 rw-p 00000000 00:00 0 [stack]
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7ffd5e2c4000-7ffd5e2e5000 rw-p 00000000 00:00 0 [stack]
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...
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Once corrected, the leading bytes should be between 7ffc and 7fff,
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rather than always being 7fff.
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Signed-off-by: Hector Marco-Gisbert <hecmargi@upv.es>
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Signed-off-by: Ismael Ripoll <iripoll@upv.es>
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[ Rebased, fixed 80 char bugs, cleaned up commit message, added test example and CVE ]
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Signed-off-by: Kees Cook <keescook@chromium.org>
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Cc: <stable@vger.kernel.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Andrew Morton <akpm@linux-foundation.org>
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Cc: Al Viro <viro@zeniv.linux.org.uk>
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Fixes: CVE-2015-1593
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Link: http://lkml.kernel.org/r/20150214173350.GA18393@www.outflux.net
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Signed-off-by: Borislav Petkov <bp@suse.de>
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---
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arch/x86/mm/mmap.c | 6 +++---
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fs/binfmt_elf.c | 5 +++--
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2 files changed, 6 insertions(+), 5 deletions(-)
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diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
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index 919b912..df4552b 100644
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--- a/arch/x86/mm/mmap.c
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+++ b/arch/x86/mm/mmap.c
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@@ -35,12 +35,12 @@ struct va_alignment __read_mostly va_align = {
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.flags = -1,
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};
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-static unsigned int stack_maxrandom_size(void)
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+static unsigned long stack_maxrandom_size(void)
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{
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- unsigned int max = 0;
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+ unsigned long max = 0;
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if ((current->flags & PF_RANDOMIZE) &&
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!(current->personality & ADDR_NO_RANDOMIZE)) {
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- max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
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+ max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
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}
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return max;
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diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
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index 02b1691..995986b 100644
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--- a/fs/binfmt_elf.c
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+++ b/fs/binfmt_elf.c
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@@ -645,11 +645,12 @@ out:
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static unsigned long randomize_stack_top(unsigned long stack_top)
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{
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- unsigned int random_variable = 0;
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+ unsigned long random_variable = 0;
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if ((current->flags & PF_RANDOMIZE) &&
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!(current->personality & ADDR_NO_RANDOMIZE)) {
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- random_variable = get_random_int() & STACK_RND_MASK;
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+ random_variable = (unsigned long) get_random_int();
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+ random_variable &= STACK_RND_MASK;
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random_variable <<= PAGE_SHIFT;
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}
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#ifdef CONFIG_STACK_GROWSUP
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--
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cgit v1.1
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