selftests/bpf: precision of a NULL global subprogram memory argument

Check that mark_chain_precision() is called for a NULL pointer passed
as a nullable pointer argument of a global subprogram.
(Pointer arguments of the global subprograms are nullable by default).

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-4-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/verifier_precision.c b/tools/testing/selftests/bpf/progs/verifier_precision.c
index 3e290b07f672..fb7dfa1246ef 100644
--- a/tools/testing/selftests/bpf/progs/verifier_precision.c
+++ b/tools/testing/selftests/bpf/progs/verifier_precision.c
@@ -676,4 +676,36 @@ __naked int null_mem_arg_zero_size(void)
 		: __clobber_all);
 }
 
+__weak int subprog_mem_arg(int *p)
+{
+	if (p)
+		return *p;
+	return 0;
+}
+
+/*
+ * Verification takes two paths: with r1 being scalar zero on path (1)
+ * and with r1 being some other scalar on path (2).
+ * Check that the verifier does not use checkpoints created
+ * on path (1) to prune path (2).
+ */
+SEC("?raw_tp")
+__flag(BPF_F_TEST_STATE_FREQ)
+__failure __msg("R1 type=scalar expected=fp")
+__naked int null_mem_arg_global_subprog(void)
+{
+	asm volatile (
+		"call %[bpf_get_prandom_u32];"
+		"r1 = 42;"
+		"if r0 > 42 goto 1f;"
+		"r1 = 0;"
+	"1:"
+		"call subprog_mem_arg;"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32)
+		: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";