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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>
This commit is contained in:
Zi Shen Lim 2016-01-13 23:33:22 -08:00 committed by David S. Miller
parent c94ae4f7c5
commit 42ff712bc0
1 changed files with 21 additions and 1 deletions
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22
arch/arm64/net/bpf_jit_comp.c
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@ -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);