Subject: [PATCH v4 11/14] sched: Reject CPU affinity changes based on arch_task_cpu_possible_mask()

From: Will Deacon <[email-masked]>
Date: Tue, 24 Nov 2020 15:50:36 +0000

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 arch_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.

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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 99992d0beb65..095deda50643 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1877,6 +1877,7 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
 					 struct rq_flags *rf)
 {
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
+	const struct cpumask *cpu_allowed_mask = arch_task_cpu_possible_mask(p);
 	unsigned int dest_cpu;
 	int ret = 0;
 
@@ -1887,6 +1888,9 @@ static int __set_cpus_allowed_ptr_locked(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;
 	}
 
 	/*
-- 
2.29.2.454.gaff20da3a2-goog

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