On 02/14, Alexei Starovoitov wrote:
From: Alexei Starovoitov <ast@xxxxxxxxxx>
The compiler is optimizing out majority of unref_ptr read/writes, so the
test
wasn't testing much. For example, one could delete '__kptr' tag from
'struct prog_test_ref_kfunc __kptr *unref_ptr;' and the test would
still "pass".
Convert it to volatile stores. Confirmed by comparing bpf asm
before/after.
Fixes: 2cbc469a6fc3 ("selftests/bpf: Add C tests for kptr")
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
tools/testing/selftests/bpf/progs/map_kptr.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/tools/testing/selftests/bpf/progs/map_kptr.c
b/tools/testing/selftests/bpf/progs/map_kptr.c
index eb8217803493..228ec45365a8 100644
--- a/tools/testing/selftests/bpf/progs/map_kptr.c
+++ b/tools/testing/selftests/bpf/progs/map_kptr.c
@@ -62,21 +62,23 @@ extern struct prog_test_ref_kfunc *
bpf_kfunc_call_test_kptr_get(struct prog_test_ref_kfunc **p, int a, int
b) __ksym;
extern void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p)
__ksym;
[..]
+#define WRITE_ONCE(x, val) ((*(volatile typeof(x) *) &(x)) = (val))
(thinking out loud)
Maybe time for us to put these into some common headers in the
selftests.
progs/test_ksyms_btf_null_check.c READ_ONCE as well..
+
static void test_kptr_unref(struct map_value *v)
{
struct prog_test_ref_kfunc *p;
p = v->unref_ptr;
/* store untrusted_ptr_or_null_ */
- v->unref_ptr = p;
+ WRITE_ONCE(v->unref_ptr, p);
if (!p)
return;
if (p->a + p->b > 100)
return;
/* store untrusted_ptr_ */
- v->unref_ptr = p;
+ WRITE_ONCE(v->unref_ptr, p);
/* store NULL */
- v->unref_ptr = NULL;
+ WRITE_ONCE(v->unref_ptr, NULL);
}
static void test_kptr_ref(struct map_value *v)
@@ -85,7 +87,7 @@ static void test_kptr_ref(struct map_value *v)
p = v->ref_ptr;
/* store ptr_or_null_ */
- v->unref_ptr = p;
+ WRITE_ONCE(v->unref_ptr, p);
if (!p)
return;
if (p->a + p->b > 100)
@@ -99,7 +101,7 @@ static void test_kptr_ref(struct map_value *v)
return;
}
/* store ptr_ */
- v->unref_ptr = p;
+ WRITE_ONCE(v->unref_ptr, p);
bpf_kfunc_call_test_release(p);
p = bpf_kfunc_call_test_acquire(&(unsigned long){0});
--
2.30.2
