This is a fix for the NX emulation patch to force the brk area well outside of the exec randomization area to avoid future allocation or brk growth collisions. Normally this isn't a problem, except when the text region has been loaded from a PIE binary and the CS limit can't be put just above bss.

A test-case that will show failures without this patch can be found here: http://bazaar.launchpad.net/~ubuntu-bugcontrol/qa-regression-testing/master/...

Signed-off-by: Kees Cook kees.cook@canonical.com --- arch/x86/kernel/process.c | 12 +++++++++++- 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 57d1868..29c0c35 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -669,6 +669,16 @@ unsigned long arch_align_stack(unsigned long sp) unsigned long arch_randomize_brk(struct mm_struct *mm) { unsigned long range_end = mm->brk + 0x02000000; - return randomize_range(mm->brk, range_end, 0) ? : mm->brk; + unsigned long bump = 0; +#ifdef CONFIG_X86_32 + /* in the case of NX emulation, shove the brk segment way out of the + way of the exec randomization area, since it can collide with + future allocations if not. */ + if ( (mm->get_unmapped_exec_area == arch_get_unmapped_exec_area) && + (mm->brk < 0x08000000) ) { + bump = (TASK_SIZE/6); + } +#endif + return bump + (randomize_range(mm->brk, range_end, 0) ? : mm->brk); }