selftests/bpf: Fix test_verifier atomic test on 32-bit

kernel-patches#20/p Can't use ATM_FETCH_ADD on kernel memory FAIL
Unexpected verifier log!
EXP: only read is supported
RES:
FAIL
Unexpected error message!
        EXP: only read is supported
        RES: 0: R1=ctx() R10=fp0
0: (79) r2 = *(u64 *)(r1 +0)
func 'bpf_fentry_test7' arg0 has btf_id 30402 type STRUCT 'bpf_fentry_test_t'
1: R1=ctx() R2_w=ptr_bpf_fentry_test_t()
1: (b7) r3 = 1                        ; R3_w=1
2: (db) r3 = atomic64_fetch_add((u64 *)(r2 +0), r3)
access beyond struct bpf_fentry_test_t at off 0 size 8
verification time 2173 usec
stack depth 0

Fixes: 98d666d ("bpf: Add tests for new BPF atomic operations")
Signed-off-by: Tony Ambardar <[email protected]>

Author: guidosarducci

tools/testing/selftests/bpf/verifier/atomic_fetch_add.c

@@ -81,6 +81,7 @@
 	 */
 	.errstr = "!read_ok",
 },
+#define BPF_PTR_SZ (sizeof(void *) == 4 ? BPF_W : BPF_DW)
 {
 	"Can't use ATM_FETCH_ADD on kernel memory",
 	.insns = {
@@ -93,7 +94,7 @@
 		 * because it's kernel memory.
 		 */
 		BPF_MOV64_IMM(BPF_REG_3, 1),
-		BPF_ATOMIC_OP(BPF_DW, BPF_ADD | BPF_FETCH, BPF_REG_2, BPF_REG_3, 0),
+		BPF_ATOMIC_OP(BPF_PTR_SZ, BPF_ADD | BPF_FETCH, BPF_REG_2, BPF_REG_3, 0),
 		/* Done */
 		BPF_MOV64_IMM(BPF_REG_0, 0),
 		BPF_EXIT_INSN(),
@@ -104,3 +105,4 @@
 	.result = REJECT,
 	.errstr = "only read is supported",
 },
+#undef BPF_PTR_SZ