[v5,09/15] sched: Reject CPU affinity changes based on task_cpu_possible_mask()

Commit Message

Will Deacon Dec. 8, 2020, 1:28 p.m. UTC

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 <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

Patch

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 58474569a2ea..92ac3e53f50a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1875,6 +1875,7 @@  static int __set_cpus_allowed_ptr(struct task_struct *p,
 				  const struct cpumask *new_mask, bool check)
 {
 	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;
@@ -1888,6 +1889,9 @@  static int __set_cpus_allowed_ptr(struct task_struct *p,
 		 * Kernel threads are allowed on online && !active CPUs
 		 */
 		cpu_valid_mask = cpu_online_mask;
+	} else if (!cpumask_subset(new_mask, cpu_allowed_mask)) {
+		ret = -EINVAL;
+		goto out;
 	}
 
 	/*