[PATCH v7 10/22] sched: Reject CPU affinity changes based on task_cpu_possible_mask()

Will Deacon
2021-05-25T15:22:19Z

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 | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 00ed51528c70..8ca7854747f1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2346,6 +2346,7 @@ 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;
@@ -2366,6 +2367,9 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
* set_cpus_allowed_common() and actually reset p->cpus_ptr.
*/
cpu_valid_mask = cpu_online_mask;
+ } else if (!cpumask_subset(new_mask, cpu_allowed_mask)) {
+ ret = -EINVAL;
+ goto out;
}

/*
--
2.31.1.818.g46aad6cb9e-goog