test_bpf: Add test to make conditional jump cross a large number of insns.

On MIPS, conditional branches can only span 32k instructions.  To
exceed this limit in the JIT with the BPF maximum of 4k insns, we need
to choose eBPF insns that expand to more than 8 machine instructions.
Use BPF_LD_ABS as it is quite complex.  This forces the JIT to invert
the sense of the branch to branch around a long jump to the end.

This (somewhat) verifies that the branch inversion logic and target
address calculation of the long jumps are done correctly.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 070bde56474cbd04e720def21c150bbc7a29bff6..c871e0e76c2a6b12c868e8ca6fb55a32bbc7b50e 100644 (file)
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -435,6 +435,30 @@ loop:
        return 0;
 }
 
+static int bpf_fill_jump_around_ld_abs(struct bpf_test *self)
+{
+       unsigned int len = BPF_MAXINSNS;
+       struct bpf_insn *insn;
+       int i = 0;
+
+       insn = kmalloc_array(len, sizeof(*insn), GFP_KERNEL);
+       if (!insn)
+               return -ENOMEM;
+
+       insn[i++] = BPF_MOV64_REG(R6, R1);
+       insn[i++] = BPF_LD_ABS(BPF_B, 0);
+       insn[i] = BPF_JMP_IMM(BPF_JEQ, R0, 10, len - i - 2);
+       i++;
+       while (i < len - 1)
+               insn[i++] = BPF_LD_ABS(BPF_B, 1);
+       insn[i] = BPF_EXIT_INSN();
+
+       self->u.ptr.insns = insn;
+       self->u.ptr.len = len;
+
+       return 0;
+}
+
 static int __bpf_fill_stxdw(struct bpf_test *self, int size)
 {
        unsigned int len = BPF_MAXINSNS;
@@ -5044,6 +5068,14 @@ static struct bpf_test tests[] = {
                { { ETH_HLEN, 0xbef } },
                .fill_helper = bpf_fill_ld_abs_vlan_push_pop,
        },
+       {
+               "BPF_MAXINSNS: jump around ld_abs",
+               { },
+               INTERNAL,
+               { 10, 11 },
+               { { 2, 10 } },
+               .fill_helper = bpf_fill_jump_around_ld_abs,
+       },
        /*
         * LD_IND / LD_ABS on fragmented SKBs
         */