Messages in this thread | | | From | Joel Fernandes <> | Date | Mon, 10 May 2021 16:47:24 -0400 | Subject | Re: [PATCH 17/19] sched: Inherit task cookie on fork() |
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On Mon, May 10, 2021 at 12:23 PM Chris Hyser <chris.hyser@oracle.com> wrote: > > On 5/10/21 12:06 PM, Joel Fernandes wrote: > > Hi Peter, > > > > On Thu, Apr 22, 2021 at 8:36 AM Peter Zijlstra <peterz@infradead.org> wrote: > >> > >> Note that sched_core_fork() is called from under tasklist_lock, and > >> not from sched_fork() earlier. This avoids a few races later. > >> > >> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > >> --- > >> include/linux/sched.h | 2 ++ > >> kernel/fork.c | 3 +++ > >> kernel/sched/core_sched.c | 6 ++++++ > >> 3 files changed, 11 insertions(+) > >> > >> --- a/include/linux/sched.h > >> +++ b/include/linux/sched.h > >> @@ -2172,8 +2172,10 @@ const struct cpumask *sched_trace_rd_spa > >> > >> #ifdef CONFIG_SCHED_CORE > >> extern void sched_core_free(struct task_struct *tsk); > >> +extern void sched_core_fork(struct task_struct *p); > >> #else > >> static inline void sched_core_free(struct task_struct *tsk) { } > >> +static inline void sched_core_fork(struct task_struct *p) { } > >> #endif > >> > >> #endif > >> --- a/kernel/fork.c > >> +++ b/kernel/fork.c > >> @@ -2249,6 +2249,8 @@ static __latent_entropy struct task_stru > >> > >> klp_copy_process(p); > >> > >> + sched_core_fork(p); > >> + > >> spin_lock(¤t->sighand->siglock); > >> > >> /* > >> @@ -2336,6 +2338,7 @@ static __latent_entropy struct task_stru > >> return p; > >> > >> bad_fork_cancel_cgroup: > >> + sched_core_free(p); > >> spin_unlock(¤t->sighand->siglock); > >> write_unlock_irq(&tasklist_lock); > >> cgroup_cancel_fork(p, args); > >> --- a/kernel/sched/core_sched.c > >> +++ b/kernel/sched/core_sched.c > >> @@ -100,6 +100,12 @@ static unsigned long sched_core_clone_co > >> return cookie; > >> } > >> > >> +void sched_core_fork(struct task_struct *p) > >> +{ > >> + RB_CLEAR_NODE(&p->core_node); > >> + p->core_cookie = sched_core_clone_cookie(current); > > > > Does this make sense also for !CLONE_THREAD forks? > > Yes. Given the absence of a cgroup interface, fork inheritance (clone the cookie) is the best way to create shared > cookie hierarchies. The security issue you mentioned was handled in my original code by setting a unique cookie on > 'exec', but Peter took that out for the reason mentioned above. It was part of the "lets get this in compromise" effort.
Thanks for sharing the history of it. I guess one can argue that this policy is better to be hardcoded in userspace since core-scheduling can be used for non-security usecases as well. Maybe one could simply call the prctl(2) from userspace if they so desire, before calling exec() ?
- Joel
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