bpf, riscv: Limit to 33 tail calls

All BPF JIT compilers except RISC-V's and MIPS' enforce a 33-tail calls
limit at runtime.  In addition, a test was recently added, in tailcalls2,
to check this limit.

This patch updates the tail call limit in RISC-V's JIT compiler to allow
33 tail calls.  I tested it using the above selftest on an emulated
RISCV64.

Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
Reported-by: Mahshid Khezri <khezri.mahshid@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@orange.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/966fe384383bf23a0ee1efe8d7291c78a3fb832b.1575916815.git.paul.chaignon@gmail.com

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index 5451ef3845f2954583cd55fac13275e49eb9b31a..7fbf56aab6610dded8a262f8f0ef74ece105e41a 100644 (file)
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -631,14 +631,14 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
                return -1;
        emit(rv_bgeu(RV_REG_A2, RV_REG_T1, off >> 1), ctx);
 
-       /* if (--TCC < 0)
+       /* if (TCC-- < 0)
         *     goto out;
         */
        emit(rv_addi(RV_REG_T1, tcc, -1), ctx);
        off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
        if (is_13b_check(off, insn))
                return -1;
-       emit(rv_blt(RV_REG_T1, RV_REG_ZERO, off >> 1), ctx);
+       emit(rv_blt(tcc, RV_REG_ZERO, off >> 1), ctx);
 
        /* prog = array->ptrs[index];
         * if (!prog)