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    Subject[PATCH 5.15 365/917] bpf/tests: Fix error in tail call limit tests
    Date
    From: Johan Almbladh <johan.almbladh@anyfinetworks.com>

    [ Upstream commit 18935a72eb25525b655262579e1652362a3b29bb ]

    This patch fixes an error in the tail call limit test that caused the
    test to fail on for x86-64 JIT. Previously, the register R0 was used to
    report the total number of tail calls made. However, after a tail call
    fall-through, the value of the R0 register is undefined. Now, all tail
    call error path tests instead use context state to store the count.

    Fixes: 874be05f525e ("bpf, tests: Add tail call test suite")
    Reported-by: Paul Chaignon <paul@cilium.io>
    Reported-by: Tiezhu Yang <yangtiezhu@loongson.cn>
    Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
    Link: https://lore.kernel.org/bpf/20210914091842.4186267-14-johan.almbladh@anyfinetworks.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    lib/test_bpf.c | 37 +++++++++++++++++++++++++++----------
    1 file changed, 27 insertions(+), 10 deletions(-)

    diff --git a/lib/test_bpf.c b/lib/test_bpf.c
    index 830a18ecffc88..68d125b409f20 100644
    --- a/lib/test_bpf.c
    +++ b/lib/test_bpf.c
    @@ -8992,10 +8992,15 @@ static __init int test_bpf(void)
    struct tail_call_test {
    const char *descr;
    struct bpf_insn insns[MAX_INSNS];
    + int flags;
    int result;
    int stack_depth;
    };

    +/* Flags that can be passed to tail call test cases */
    +#define FLAG_NEED_STATE BIT(0)
    +#define FLAG_RESULT_IN_STATE BIT(1)
    +
    /*
    * Magic marker used in test snippets for tail calls below.
    * BPF_LD/MOV to R2 and R2 with this immediate value is replaced
    @@ -9065,32 +9070,38 @@ static struct tail_call_test tail_call_tests[] = {
    {
    "Tail call error path, max count reached",
    .insns = {
    - BPF_ALU64_IMM(BPF_ADD, R1, 1),
    - BPF_ALU64_REG(BPF_MOV, R0, R1),
    + BPF_LDX_MEM(BPF_W, R2, R1, 0),
    + BPF_ALU64_IMM(BPF_ADD, R2, 1),
    + BPF_STX_MEM(BPF_W, R1, R2, 0),
    TAIL_CALL(0),
    BPF_EXIT_INSN(),
    },
    - .result = MAX_TAIL_CALL_CNT + 1,
    + .flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,
    + .result = (MAX_TAIL_CALL_CNT + 1 + 1) * MAX_TESTRUNS,
    },
    {
    "Tail call error path, NULL target",
    .insns = {
    - BPF_ALU64_IMM(BPF_MOV, R0, -1),
    + BPF_LDX_MEM(BPF_W, R2, R1, 0),
    + BPF_ALU64_IMM(BPF_ADD, R2, 1),
    + BPF_STX_MEM(BPF_W, R1, R2, 0),
    TAIL_CALL(TAIL_CALL_NULL),
    - BPF_ALU64_IMM(BPF_MOV, R0, 1),
    BPF_EXIT_INSN(),
    },
    - .result = 1,
    + .flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,
    + .result = MAX_TESTRUNS,
    },
    {
    "Tail call error path, index out of range",
    .insns = {
    - BPF_ALU64_IMM(BPF_MOV, R0, -1),
    + BPF_LDX_MEM(BPF_W, R2, R1, 0),
    + BPF_ALU64_IMM(BPF_ADD, R2, 1),
    + BPF_STX_MEM(BPF_W, R1, R2, 0),
    TAIL_CALL(TAIL_CALL_INVALID),
    - BPF_ALU64_IMM(BPF_MOV, R0, 1),
    BPF_EXIT_INSN(),
    },
    - .result = 1,
    + .flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,
    + .result = MAX_TESTRUNS,
    },
    };

    @@ -9196,6 +9207,8 @@ static __init int test_tail_calls(struct bpf_array *progs)
    for (i = 0; i < ARRAY_SIZE(tail_call_tests); i++) {
    struct tail_call_test *test = &tail_call_tests[i];
    struct bpf_prog *fp = progs->ptrs[i];
    + int *data = NULL;
    + int state = 0;
    u64 duration;
    int ret;

    @@ -9212,7 +9225,11 @@ static __init int test_tail_calls(struct bpf_array *progs)
    if (fp->jited)
    jit_cnt++;

    - ret = __run_one(fp, NULL, MAX_TESTRUNS, &duration);
    + if (test->flags & FLAG_NEED_STATE)
    + data = &state;
    + ret = __run_one(fp, data, MAX_TESTRUNS, &duration);
    + if (test->flags & FLAG_RESULT_IN_STATE)
    + ret = state;
    if (ret == test->result) {
    pr_cont("%lld PASS", duration);
    pass_cnt++;
    --
    2.33.0


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