[PATCH AUTOSEL 5.4 01/10] selftests/bpf: Verify copy_register_state() preserves parent/live fields

Sasha Levin
2023-02-09T11:27:06Z

From: Eduard Zingerman <eddyz87@gmail.com>

[ Upstream commit b9fa9bc839291020b362ab5392e5f18ba79657ac ]

A testcase to check that verifier.c:copy_register_state() preserves
register parentage chain and livness information.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230106142214.1040390-3-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
.../selftests/bpf/verifier/search_pruning.c | 36 +++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/tools/testing/selftests/bpf/verifier/search_pruning.c b/tools/testing/selftests/bpf/verifier/search_pruning.c
index 7e50cb80873a5..7e36078f8f482 100644
--- a/tools/testing/selftests/bpf/verifier/search_pruning.c
+++ b/tools/testing/selftests/bpf/verifier/search_pruning.c
@@ -154,3 +154,39 @@
.result_unpriv = ACCEPT,
.insn_processed = 15,
},
+/* The test performs a conditional 64-bit write to a stack location
+ * fp[-8], this is followed by an unconditional 8-bit write to fp[-8],
+ * then data is read from fp[-8]. This sequence is unsafe.
+ *
+ * The test would be mistakenly marked as safe w/o dst register parent
+ * preservation in verifier.c:copy_register_state() function.
+ *
+ * Note the usage of BPF_F_TEST_STATE_FREQ to force creation of the
+ * checkpoint state after conditional 64-bit assignment.
+ */
+{
+ "write tracking and register parent chain bug",
+ .insns = {
+ /* r6 = ktime_get_ns() */
+ BPF_EMIT_CALL(BPF_FUNC_ktime_get_ns),
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
+ /* r0 = ktime_get_ns() */
+ BPF_EMIT_CALL(BPF_FUNC_ktime_get_ns),
+ /* if r0 > r6 goto +1 */
+ BPF_JMP_REG(BPF_JGT, BPF_REG_0, BPF_REG_6, 1),
+ /* *(u64 *)(r10 - 8) = 0xdeadbeef */
+ BPF_ST_MEM(BPF_DW, BPF_REG_FP, -8, 0xdeadbeef),
+ /* r1 = 42 */
+ BPF_MOV64_IMM(BPF_REG_1, 42),
+ /* *(u8 *)(r10 - 8) = r1 */
+ BPF_STX_MEM(BPF_B, BPF_REG_FP, BPF_REG_1, -8),
+ /* r2 = *(u64 *)(r10 - 8) */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_FP, -8),
+ /* exit(0) */
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ },
+ .flags = BPF_F_TEST_STATE_FREQ,
+ .errstr = "invalid read from stack off -8+1 size 8",
+ .result = REJECT,
+},
--
2.39.0