[PATCH v8 08/19] sched: Reject CPU affinity changes based on task_cpu_possible_mask()

Will Deacon
2021-06-02T16:52:47Z

Reject explicit requests to change the affinity mask of a task via
set_cpus_allowed_ptr() if the requested mask is not a subset of the
mask returned by task_cpu_possible_mask(). This ensures that the
'cpus_mask' for a given task cannot contain CPUs which are incapable of
executing it, except in cases where the affinity is forced.

Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
kernel/sched/core.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c1b6f1a6c91..b23c7f0ab31a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2347,15 +2347,17 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
u32 flags)
{
const struct cpumask *cpu_valid_mask = cpu_active_mask;
+ const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
unsigned int dest_cpu;
struct rq_flags rf;
struct rq *rq;
int ret = 0;
+ bool kthread = p->flags & PF_KTHREAD;

rq = task_rq_lock(p, &rf);
update_rq_clock(rq);

- if (p->flags & PF_KTHREAD || is_migration_disabled(p)) {
+ if (kthread || is_migration_disabled(p)) {
/*
* Kernel threads are allowed on online && !active CPUs,
* however, during cpu-hot-unplug, even these might get pushed
@@ -2369,6 +2371,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
cpu_valid_mask = cpu_online_mask;
}

+ if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
+ ret = -EINVAL;
+ goto out;
+ }
+
/*
* Must re-check here, to close a race against __kthread_bind(),
* sched_setaffinity() is not guaranteed to observe the flag.
--
2.32.0.rc0.204.g9fa02ecfa5-goog