"Implement" mbind(2).

We still only advertise a single NUMA node, and ignore mempolicy
accordingly, but mbind() at least now succeeds and has effects reflected
by get_mempolicy().

Also fix handling of nodemasks: round sizes to unsigned long (as
documented and done by Linux), and zero trailing bits when copying them
out.

PiperOrigin-RevId: 251950859

2 files changed, 6 insertions, 5 deletions

diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index f9378c2de..4d889422f 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -455,12 +455,13 @@ type Task struct {
 	// single numa node, all policies are no-ops. We only track this information
 	// so that we can return reasonable values if the application calls
 	// get_mempolicy(2) after setting a non-default policy. Note that in the
-	// real syscall, nodemask can be longer than 4 bytes, but we always report a
-	// single node so never need to save more than a single bit.
+	// real syscall, nodemask can be longer than a single unsigned long, but we
+	// always report a single node so never need to save more than a single
+	// bit.
 	//
 	// numaPolicy and numaNodeMask are protected by mu.
 	numaPolicy   int32
-	numaNodeMask uint32
+	numaNodeMask uint64
 
 	// If netns is true, the task is in a non-root network namespace. Network
 	// namespaces aren't currently implemented in full; being in a network
diff --git a/pkg/sentry/kernel/task_sched.go b/pkg/sentry/kernel/task_sched.go
index 5455f6ea9..1c94ab11b 100644
--- a/pkg/sentry/kernel/task_sched.go
+++ b/pkg/sentry/kernel/task_sched.go
@@ -622,14 +622,14 @@ func (t *Task) SetNiceness(n int) {
 }
 
 // NumaPolicy returns t's current numa policy.
-func (t *Task) NumaPolicy() (policy int32, nodeMask uint32) {
+func (t *Task) NumaPolicy() (policy int32, nodeMask uint64) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 	return t.numaPolicy, t.numaNodeMask
 }
 
 // SetNumaPolicy sets t's numa policy.
-func (t *Task) SetNumaPolicy(policy int32, nodeMask uint32) {
+func (t *Task) SetNumaPolicy(policy int32, nodeMask uint64) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 	t.numaPolicy = policy