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authorJunjie Mao <eternal.n08@gmail.com>2014-10-31 21:40:38 +0800
committerThomas Gleixner <tglx@linutronix.de>2014-11-01 22:20:50 +0100
commite6023367d779060fddc9a52d1f474085b2b36298 (patch)
treeef35781f63032842e6cf8b3e1869d54f312ce17f /arch/x86/tools
parent4750a0d112cbfcc744929f1530ffe3193436766c (diff)
downloadlinux-e6023367d779060fddc9a52d1f474085b2b36298.tar.bz2
x86, kaslr: Prevent .bss from overlaping initrd
When choosing a random address, the current implementation does not take into account the reversed space for .bss and .brk sections. Thus the relocated kernel may overlap other components in memory. Here is an example of the overlap from a x86_64 kernel in qemu (the ranges of physical addresses are presented): Physical Address 0x0fe00000 --+--------------------+ <-- randomized base / | relocated kernel | vmlinux.bin | (from vmlinux.bin) | 0x1336d000 (an ELF file) +--------------------+-- \ | | \ 0x1376d870 --+--------------------+ | | relocs table | | 0x13c1c2a8 +--------------------+ .bss and .brk | | | 0x13ce6000 +--------------------+ | | | / 0x13f77000 | initrd |-- | | 0x13fef374 +--------------------+ The initrd image will then be overwritten by the memset during early initialization: [ 1.655204] Unpacking initramfs... [ 1.662831] Initramfs unpacking failed: junk in compressed archive This patch prevents the above situation by requiring a larger space when looking for a random kernel base, so that existing logic can effectively avoids the overlap. [kees: switched to perl to avoid hex translation pain in mawk vs gawk] [kees: calculated overlap without relocs table] Fixes: 82fa9637a2 ("x86, kaslr: Select random position from e820 maps") Reported-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Junjie Mao <eternal.n08@gmail.com> Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Matt Fleming <matt.fleming@intel.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1414762838-13067-1-git-send-email-eternal.n08@gmail.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/tools')
-rw-r--r--arch/x86/tools/calc_run_size.pl30
1 files changed, 30 insertions, 0 deletions
diff --git a/arch/x86/tools/calc_run_size.pl b/arch/x86/tools/calc_run_size.pl
new file mode 100644
index 000000000000..0b0b124d3ece
--- /dev/null
+++ b/arch/x86/tools/calc_run_size.pl
@@ -0,0 +1,30 @@
+#!/usr/bin/perl
+#
+# Calculate the amount of space needed to run the kernel, including room for
+# the .bss and .brk sections.
+#
+# Usage:
+# objdump -h a.out | perl calc_run_size.pl
+use strict;
+
+my $mem_size = 0;
+my $file_offset = 0;
+
+my $sections=" *[0-9]+ \.(?:bss|brk) +";
+while (<>) {
+ if (/^$sections([0-9a-f]+) +(?:[0-9a-f]+ +){2}([0-9a-f]+)/) {
+ my $size = hex($1);
+ my $offset = hex($2);
+ $mem_size += $size;
+ if ($file_offset == 0) {
+ $file_offset = $offset;
+ } elsif ($file_offset != $offset) {
+ die ".bss and .brk lack common file offset\n";
+ }
+ }
+}
+
+if ($file_offset == 0) {
+ die "Never found .bss or .brk file offset\n";
+}
+printf("%d\n", $mem_size + $file_offset);