On 8/11/24 10:21 PM, Yonghong Song wrote:
A selftest is added such that without the previous patch,
a crash can happen. With the previous patch, the test can
run successfully. The new test is written in a way which
mimics original crash case:
main_prog
static_prog_1
static_prog_2
where static_prog_1 has different paths to static_prog_2
and some path has stack allocated and some other path
does not. A stacksafe() checking in static_prog_2()
triggered the crash.
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
tools/testing/selftests/bpf/progs/iters.c | 54 +++++++++++++++++++++++
1 file changed, 54 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/iters.c b/tools/testing/selftests/bpf/progs/iters.c
index 16bdc3e25591..8d3b75147617 100644
--- a/tools/testing/selftests/bpf/progs/iters.c
+++ b/tools/testing/selftests/bpf/progs/iters.c
@@ -1432,4 +1432,58 @@ int iter_arr_with_actual_elem_count(const void *ctx)
return sum;
}
+__u32 upper, select_n, result;
+__u64 global;
+
+static __noinline bool nest_2(char *str, int len)
Argument 'len' is not needed here. I can make the change after some
additional comments.
+{
+ /* some insns (including branch insns) to ensure stacksafe() is triggered
+ * in nest_2(). This way, stacksafe() can compare frame associated with nest_1().
+ */
+ if (str[0] == 't')
+ return true;
+ if (str[1] == 'e')
+ return true;
+ if (str[2] == 's')
+ return true;
+ if (str[3] == 't')
+ return true;
+ return false;
+}
+
+static __noinline bool nest_1(int n)
+{
+ /* case 0: allocate stack, case 1: no allocate stack */
+ switch (n) {
+ case 0: {
+ char comm[16];
+
+ if (bpf_get_current_comm(comm, 16))
+ return false;
+ return nest_2(comm, 16);
+ }
+ case 1:
+ return nest_2((char *)&global, sizeof(global));
+ default:
+ return false;
+ }
To triger the failure, we rely on 'case 0' is explored by the verifier first
and 'case 1' is explored later. This seems the case for llvm18 and llvm20.
+}
+
+SEC("raw_tp")
+__success
+int iter_subprog_check_stacksafe(const void *ctx)
+{
+ long i;
+
+ bpf_for(i, 0, upper) {
+ if (!nest_1(select_n)) {
+ result = 1;
+ return 0;
+ }
+ }
+
+ result = 2;
+ return 0;
+}
+
char _license[] SEC("license") = "GPL";
