riscv, bpf: Emit fixed-length instructions for BPF_PSEUDO_FUNC

For BPF_PSEUDO_FUNC instruction, verifier will refill imm with
correct addresses of bpf_calls and then run last pass of JIT.
Since the emit_imm of RV64 is variable-length, which will emit
appropriate length instructions accorroding to the imm, it may
broke ctx->offset, and lead to unpredictable problem, such as
inaccurate jump. So let's fix it with fixed-length instructions.

Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
Suggested-by: Björn Töpel <bjorn@rivosinc.com>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Björn Töpel <bjorn@kernel.org>
Acked-by: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/bpf/20221206091410.1584784-1-pulehui@huaweicloud.com

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 00df3a8f92acd8d23c7253e1e15fb0af1a5cb8d8..f2417ac54edd6db01ab3cbdd2bd1d5be3fc942ab 100644 (file)
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -136,6 +136,25 @@ static bool in_auipc_jalr_range(s64 val)
                val < ((1L << 31) - (1L << 11));
 }
 
+/* Emit fixed-length instructions for address */
+static int emit_addr(u8 rd, u64 addr, bool extra_pass, struct rv_jit_context *ctx)
+{
+       u64 ip = (u64)(ctx->insns + ctx->ninsns);
+       s64 off = addr - ip;
+       s64 upper = (off + (1 << 11)) >> 12;
+       s64 lower = off & 0xfff;
+
+       if (extra_pass && !in_auipc_jalr_range(off)) {
+               pr_err("bpf-jit: target offset 0x%llx is out of range\n", off);
+               return -ERANGE;
+       }
+
+       emit(rv_auipc(rd, upper), ctx);
+       emit(rv_addi(rd, rd, lower), ctx);
+       return 0;
+}
+
+/* Emit variable-length instructions for 32-bit and 64-bit imm */
 static void emit_imm(u8 rd, s64 val, struct rv_jit_context *ctx)
 {
        /* Note that the immediate from the add is sign-extended,
@@ -1050,7 +1069,15 @@ out_be:
                u64 imm64;
 
                imm64 = (u64)insn1.imm << 32 | (u32)imm;
-               emit_imm(rd, imm64, ctx);
+               if (bpf_pseudo_func(insn)) {
+                       /* fixed-length insns for extra jit pass */
+                       ret = emit_addr(rd, imm64, extra_pass, ctx);
+                       if (ret)
+                               return ret;
+               } else {
+                       emit_imm(rd, imm64, ctx);
+               }
+
                return 1;
        }