[bpf-next v3 12/12] selftests/bpf: Test correctness of narrow 32bit read on 64bit field

[Krzesimir Nowak <krzesimir@kinvolk.io>]

Test the correctness of the 32bit narrow reads by reading both halves
of the 64 bit field and doing a binary or on them to see if we get the
original value.

It succeeds as it should, but with the commit e2f7fc0ac695 ("bpf: fix
undefined behavior in narrow load handling") reverted, the test fails
with a following message:

> $ sudo ./test_verifier
> ...
> #967/p 32bit loads of a 64bit field (both least and most significant words) FAIL retval -1985229329 != 0
> verification time 17 usec
> stack depth 0
> processed 8 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
> ...
> Summary: 1519 PASSED, 0 SKIPPED, 1 FAILED

Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
---
 tools/testing/selftests/bpf/test_verifier.c   | 19 +++++++++++++++++
 .../testing/selftests/bpf/verifier/var_off.c  | 21 +++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 484ea8842b06..2a20280a4a44 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -24,6 +24,7 @@
 
 #include <sys/capability.h>
 
+#include <linux/compiler.h>
 #include <linux/unistd.h>
 #include <linux/filter.h>
 #include <linux/bpf_perf_event.h>
@@ -343,6 +344,24 @@ static void bpf_fill_perf_event_test_run_check(struct bpf_test *self)
 	self->fill_insns = NULL;
 }
 
+static void bpf_fill_32bit_loads(struct bpf_test *self)
+{
+	compiletime_assert(
+		sizeof(struct bpf_perf_event_data) <= TEST_CTX_LEN,
+		"buffer for ctx is too short to fit struct bpf_perf_event_data");
+	compiletime_assert(
+		sizeof(struct bpf_perf_event_value) <= TEST_DATA_LEN,
+		"buffer for data is too short to fit struct bpf_perf_event_value");
+
+	struct bpf_perf_event_data ctx = {
+		.sample_period = 0x0123456789abcdef,
+	};
+
+	memcpy(self->ctx, &ctx, sizeof(ctx));
+	free(self->fill_insns);
+	self->fill_insns = NULL;
+}
+
 /* BPF_SK_LOOKUP contains 13 instructions, if you need to fix up maps */
 #define BPF_SK_LOOKUP(func)						\
 	/* struct bpf_sock_tuple tuple = {} */				\
diff --git a/tools/testing/selftests/bpf/verifier/var_off.c b/tools/testing/selftests/bpf/verifier/var_off.c
index 8504ac937809..3f8bee0a50ef 100644
--- a/tools/testing/selftests/bpf/verifier/var_off.c
+++ b/tools/testing/selftests/bpf/verifier/var_off.c
@@ -246,3 +246,24 @@
 	.result = ACCEPT,
 	.prog_type = BPF_PROG_TYPE_LWT_IN,
 },
+{
+	"32bit loads of a 64bit field (both least and most significant words)",
+	.insns = {
+	BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period)),
+	BPF_LDX_MEM(BPF_W, BPF_REG_5, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period) + 4),
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period)),
+	BPF_ALU64_IMM(BPF_LSH, BPF_REG_5, 32),
+	BPF_ALU64_REG(BPF_OR, BPF_REG_4, BPF_REG_5),
+	BPF_ALU64_REG(BPF_XOR, BPF_REG_4, BPF_REG_6),
+	BPF_MOV64_REG(BPF_REG_0, BPF_REG_4),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+	.prog_type = BPF_PROG_TYPE_PERF_EVENT,
+	.ctx = { 0, },
+	.ctx_len = sizeof(struct bpf_perf_event_data),
+	.data = { 0, },
+	.data_len = sizeof(struct bpf_perf_event_value),
+	.fill_helper = bpf_fill_32bit_loads,
+	.override_data_out_len = true,
+},
-- 
2.20.1