[PATCH bpf v1 6/8] selftests/bpf: Check faultable stack helper contexts

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add verifier coverage for the sleepable bpf_get_stack() and
bpf_get_task_stack() implementations. Call each helper while preemption is
disabled and require the verifier to reject it as sleepable.

Both programs load when the prototypes lack might_sleep, so the
expected-failure tests fail. Keep success controls outside the
non-preemptible region to ensure ordinary calls from sleepable uprobes
remain valid.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../selftests/bpf/progs/preempt_lock.c        | 52 +++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/preempt_lock.c b/tools/testing/selftests/bpf/progs/preempt_lock.c
index 6d5fce7e6ffc..81c459435680 100644
--- a/tools/testing/selftests/bpf/progs/preempt_lock.c
+++ b/tools/testing/selftests/bpf/progs/preempt_lock.c
@@ -115,6 +115,58 @@ int preempt_sleepable_helper(void *ctx)
 	return 0;
 }
 
+SEC("?uprobe.s")
+__failure __msg("sleepable helper bpf_get_stack#")
+int preempt_sleepable_get_stack(struct pt_regs *ctx)
+{
+	struct bpf_stack_build_id stack;
+
+	bpf_preempt_disable();
+	bpf_get_stack(ctx, &stack, sizeof(stack),
+		      BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
+	bpf_preempt_enable();
+	return 0;
+}
+
+SEC("?uprobe.s")
+__failure __msg("sleepable helper bpf_get_task_stack#")
+int preempt_sleepable_get_task_stack(void *ctx)
+{
+	struct bpf_stack_build_id stack;
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf();
+	bpf_preempt_disable();
+	bpf_get_task_stack(task, &stack, sizeof(stack),
+			   BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
+	bpf_preempt_enable();
+	return 0;
+}
+
+SEC("?uprobe.s")
+__success
+int sleepable_get_stack(struct pt_regs *ctx)
+{
+	struct bpf_stack_build_id stack;
+
+	bpf_get_stack(ctx, &stack, sizeof(stack),
+		      BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
+	return 0;
+}
+
+SEC("?uprobe.s")
+__success
+int sleepable_get_task_stack(void *ctx)
+{
+	struct bpf_stack_build_id stack;
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf();
+	bpf_get_task_stack(task, &stack, sizeof(stack),
+			   BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
+	return 0;
+}
+
 SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
 __failure __msg("kernel func bpf_copy_from_user_str is sleepable within non-preemptible region")
 int preempt_sleepable_kfunc(void *ctx)
-- 
2.53.0