On Mon, Oct 31, 2016 at 7:04 AM, Jann Horn <j...@thejh.net> wrote: > On machines with sizeof(unsigned long)==8, this ensures that the more > significant 32 bits of stack_canary are random, too. > stack_canary is defined as unsigned long, all the architectures with stack > protector support already pick the stack_canary of init as a random > unsigned long, and get_random_long() should be as fast as get_random_int(), > so there seems to be no good reason against this. > > This should help if someone tries to guess a stack canary with brute force. > > (This change has been made in PaX already, with a different RNG.) > > Signed-off-by: Jann Horn <j...@thejh.net>
Acked-by: Kees Cook <keesc...@chromium.org> (A separate change might be to make sure that the leading byte is zeroed. Entropy of the value, I think, is less important than blocking canary exposures from unbounded str* functions. Brute forcing kernel stack canaries isn't like it bruting them in userspace...) -Kees > --- > kernel/fork.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 623259fc794d..d577e2c5d14f 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -518,7 +518,7 @@ static struct task_struct *dup_task_struct(struct > task_struct *orig, int node) > set_task_stack_end_magic(tsk); > > #ifdef CONFIG_CC_STACKPROTECTOR > - tsk->stack_canary = get_random_int(); > + tsk->stack_canary = get_random_long(); > #endif > > /* > -- > 2.1.4 > -- Kees Cook Nexus Security
