Patch "selftests/bpf: Fix map_kptr test." has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    selftests/bpf: Fix map_kptr test.

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     selftests-bpf-fix-map_kptr-test.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0fb12aa8742daf092b1cba977da0381c7e5b9598
Author: Alexei Starovoitov <ast@xxxxxxxxxx>
Date:   Tue Feb 14 15:50:51 2023 -0800

    selftests/bpf: Fix map_kptr test.
    
    [ Upstream commit 62d101d5f422cde39b269f7eb4cbbe2f1e26f9d4 ]
    
    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>
    Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20230214235051.22938-1-alexei.starovoitov@xxxxxxxxx
    Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/testing/selftests/bpf/progs/map_kptr.c b/tools/testing/selftests/bpf/progs/map_kptr.c
index eb82178034934..228ec45365a8d 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))
+
 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});