On 7/28/21 10:05 AM, Johan Almbladh wrote:
While BPF_CALL instructions were tested implicitly by the cBPF-to-eBPF
translation, there has not been any tests for BPF_TAIL_CALL instructions.
The new test suite includes tests for tail call chaining, tail call count
tracking and error paths. It is mainly intended for JIT development and
testing.
Signed-off-by: Johan Almbladh <johan.almbladh@xxxxxxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
The above Reported-by tag can be removed. This patch itself is not
about fixing an issue reported by kernel test robot...
The patch looks good to me except a few minor comments below.
Acked-by: Yonghong Song <yhs@xxxxxx>
---
lib/test_bpf.c | 249 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 249 insertions(+)
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index af5758151d0a..222d454b2ed4 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -8981,8 +8981,249 @@ static __init int test_bpf(void)
return err_cnt ? -EINVAL : 0;
}
+struct tail_call_test {
+ const char *descr;
+ struct bpf_insn insns[MAX_INSNS];
+ int result;
+ int stack_depth;
+};
+
+/*
+ * Magic marker used in test snippets for tail calls below.
+ * BPF_LD/MOV to R2 and R2 with this immediate value is replaced
+ * with the proper values by the test runner.
+ */
+#define TAIL_CALL_MARKER 0x7a11ca11
+
+/* Special offset to indicate a NULL call target */
+#define TAIL_CALL_NULL 0x7fff
+
+#define TAIL_CALL(offset) \
+ BPF_LD_IMM64(R2, TAIL_CALL_MARKER), \
+ BPF_RAW_INSN(BPF_ALU | BPF_MOV | BPF_K, R3, 0, \
+ offset, TAIL_CALL_MARKER), \
+ BPF_JMP_IMM(BPF_TAIL_CALL, 0, 0, 0)
+
+/*
+ * Tail call tests. Each test case may call any other test in the table,
+ * including itself, specified as a relative index offset from the calling
+ * test. The index TAIL_CALL_NULL can be used to specify a NULL target
+ * function to test the JIT error path.
+ */
+static struct tail_call_test tail_call_tests[] = {
+ {
+ "Tail call leaf",
+ .insns = {
+ BPF_ALU64_REG(BPF_MOV, R0, R1),
+ BPF_ALU64_IMM(BPF_ADD, R0, 1),
+ BPF_EXIT_INSN(),
+ },
+ .result = 1,
+ },
+ {
+ "Tail call 2",
+ .insns = {
+ BPF_ALU64_IMM(BPF_ADD, R1, 2),
+ TAIL_CALL(-1),
+ BPF_ALU64_IMM(BPF_MOV, R0, -1),
+ BPF_EXIT_INSN(),
+ },
+ .result = 3,
+ },
+ {
+ "Tail call 3",
+ .insns = {
+ BPF_ALU64_IMM(BPF_ADD, R1, 3),
+ TAIL_CALL(-1),
+ BPF_ALU64_IMM(BPF_MOV, R0, -1),
+ BPF_EXIT_INSN(),
+ },
+ .result = 6,
+ },
+ {
+ "Tail call 4",
+ .insns = {
+ BPF_ALU64_IMM(BPF_ADD, R1, 4),
+ TAIL_CALL(-1),
+ BPF_ALU64_IMM(BPF_MOV, R0, -1),
+ BPF_EXIT_INSN(),
+ },
+ .result = 10,
+ },
+ {
+ "Tail call error path, max count reached",
+ .insns = {
+ BPF_ALU64_IMM(BPF_ADD, R1, 1),
+ BPF_ALU64_REG(BPF_MOV, R0, R1),
+ TAIL_CALL(0),
+ BPF_EXIT_INSN(),
+ },
+ .result = MAX_TAIL_CALL_CNT + 1,
+ },
+ {
+ "Tail call error path, NULL target",
+ .insns = {
+ BPF_ALU64_IMM(BPF_MOV, R0, -1),
+ TAIL_CALL(TAIL_CALL_NULL),
+ BPF_ALU64_IMM(BPF_MOV, R0, 1),
+ BPF_EXIT_INSN(),
+ },
+ .result = 1,
+ },
+ {
+ /* Must be the last test */
+ "Tail call error path, index out of range",
+ .insns = {
+ BPF_ALU64_IMM(BPF_MOV, R0, -1),
+ TAIL_CALL(1), /* Index out of range */
+ BPF_ALU64_IMM(BPF_MOV, R0, 1),
+ BPF_EXIT_INSN(),
+ },
+ .result = 1,
+ },
+};
+
+static void __init destroy_tail_call_tests(struct bpf_array *progs)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(tail_call_tests); i++)
+ if (progs->ptrs[i])
+ bpf_prog_free(progs->ptrs[i]);
+ kfree(progs);
+}
+
+static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
+{
+ struct bpf_array *progs;
+ int ntests = ARRAY_SIZE(tail_call_tests);
+ int which, err;
reverse christmas tree?
+
+ /* Allocate the table of programs to be used for tall calls */
+ progs = kzalloc(sizeof(*progs) + (ntests + 1) * sizeof(progs->ptrs[0]),
+ GFP_KERNEL);
+ if (!progs)
+ goto out_nomem;
+
+ /* Create all eBPF programs and populate the table */
+ for (which = 0; which < ntests; which++) {
+ struct tail_call_test *test = &tail_call_tests[which];
+ struct bpf_prog *fp;
+ int len, i;
+
+ /* Compute the number of program instructions */
+ for (len = 0; len < MAX_INSNS; len++) {
+ struct bpf_insn *insn = &test->insns[len];
+
+ if (len < MAX_INSNS - 1 &&
+ insn->code == (BPF_LD | BPF_DW | BPF_IMM))
+ len++;
+ if (insn->code == 0)
+ break;
+ }
+
+ /* Allocate and initialize the program */
+ fp = bpf_prog_alloc(bpf_prog_size(len), 0);
+ if (!fp)
+ goto out_nomem;
+
+ fp->len = len;
+ fp->type = BPF_PROG_TYPE_SOCKET_FILTER;
+ fp->aux->stack_depth = test->stack_depth;
+ memcpy(fp->insnsi, test->insns, len * sizeof(struct bpf_insn));
+
+ /* Relocate runtime tail call offsets and addresses */
+ for (i = 0; i < len; i++) {
+ struct bpf_insn *insn = &fp->insnsi[i];
+ int target;
+
+ if (insn->imm != TAIL_CALL_MARKER)
+ continue;
+
+ switch (insn->code) {
+ case BPF_LD | BPF_DW | BPF_IMM:
+ if (insn->dst_reg == R2) {
Looks like the above condition is not needed. It is always true.
+ insn[0].imm = (u32)(long)progs;
+ insn[1].imm = ((u64)(long)progs) >> 32;
+ }
+ break;
+
+ case BPF_ALU | BPF_MOV | BPF_K:
+ case BPF_ALU64 | BPF_MOV | BPF_K:
case BPF_ALU64 | BPF_MOV | BPF_K is not needed.
+ if (insn->off == TAIL_CALL_NULL)
+ target = ntests;
+ else
+ target = which + insn->off;
+ if (insn->dst_reg == R3)
the same here, insn->dst_reg == R3 is not needed. It is always true.
I suggest to set insn->off = 0. Otherwise, it is an illegal insn.
We won't issue here because we didn't invoke verifier. It is still
good to make the insn legel.
+ insn->imm = target;
+ break;
+ }
+ }
+
+ fp = bpf_prog_select_runtime(fp, &err);
+ if (err)
+ goto out_err;
+
+ progs->ptrs[which] = fp;
+ }
+
+ /* The last entry contains a NULL program pointer */
+ progs->map.max_entries = ntests + 1;
+ *pprogs = progs;
+ return 0;
+
+out_nomem:
+ err = -ENOMEM;
+
+out_err:
+ if (progs)
+ destroy_tail_call_tests(progs);
+ return err;
+}
+
[...]
