arm64: bpf: add extra pass to handle faulty codegen

Code generation functions in arch/arm64/kernel/insn.c previously
BUG_ON invalid parameters. Following change of that behavior, now we
need to handle the error case where AARCH64_BREAK_FAULT is returned.

Instead of error-handling on every emit() in JIT, we add a new
validation pass at the end of JIT compilation. There's no point in
running JITed code at run-time only to trap due to AARCH64_BREAK_FAULT.
Instead, we drop this failed JIT compilation and allow the system to
gracefully fallback on the BPF interpreter.

Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com>
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 7658612d915caaf11c1c5df8743994e0c87a3412..a34420a5df9a2e5134beb26964f08c57d97c0d16 100644 (file)
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1,7 +1,7 @@
 /*
  * BPF JIT compiler for ARM64
  *
- * Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx@gmail.com>
+ * Copyright (C) 2014-2016 Zi Shen Lim <zlim.lnx@gmail.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -737,6 +737,20 @@ static int build_body(struct jit_ctx *ctx)
        return 0;
 }
 
+static int validate_code(struct jit_ctx *ctx)
+{
+       int i;
+
+       for (i = 0; i < ctx->idx; i++) {
+               u32 a64_insn = le32_to_cpu(ctx->image[i]);
+
+               if (a64_insn == AARCH64_BREAK_FAULT)
+                       return -1;
+       }
+
+       return 0;
+}
+
 static inline void bpf_flush_icache(void *start, void *end)
 {
        flush_icache_range((unsigned long)start, (unsigned long)end);
@@ -799,6 +813,12 @@ void bpf_int_jit_compile(struct bpf_prog *prog)
 
        build_epilogue(&ctx);
 
+       /* 3. Extra pass to validate JITed code. */
+       if (validate_code(&ctx)) {
+               bpf_jit_binary_free(header);
+               goto out;
+       }
+
        /* And we're done. */
        if (bpf_jit_enable > 1)
                bpf_jit_dump(prog->len, image_size, 2, ctx.image);