On Mon, May 27, 2019 at 03:23:08PM +0800, Dianzhang Chen wrote: > The `resource` in do_prlimit() is controlled by userspace via syscall: > setrlimit(defined in kernel/sys.c), hence leading to a potential exploitation > of the Spectre variant 1 vulnerability. > The relevant code in do_prlimit() is as below: > > if (resource >= RLIM_NLIMITS) > return -EINVAL; > ... > rlim = tsk->signal->rlim + resource; // use resource as index > ... > *old_rlim = *rlim; > > Fix this by sanitizing resource before using it to index tsk->signal->rlim. > > Signed-off-by: Dianzhang Chen <dianzhangch...@gmail.com> > --- > kernel/sys.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/sys.c b/kernel/sys.c > index bdbfe8d..7eba1ca 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1532,6 +1532,8 @@ int do_prlimit(struct task_struct *tsk, unsigned int > resource, > > if (resource >= RLIM_NLIMITS) > return -EINVAL; > + > + resource = array_index_nospec(resource, RLIM_NLIMITS); > if (new_rlim) { > if (new_rlim->rlim_cur > new_rlim->rlim_max) > return -EINVAL;
Could you please explain in details how array_index_nospec is different from resource >= RLIM_NLIMITS? Since I don't get how it is related to spectre issue.