提交 51c9fbb1 编写于 作者: Z Zi Shen Lim 提交者: Will Deacon

arm64: bpf: lift restriction on last instruction

Earlier implementation assumed last instruction is BPF_EXIT.
Since this is no longer a restriction in eBPF, we remove this
limitation.

Per Alexei Starovoitov [1]:
> classic BPF has a restriction that last insn is always BPF_RET.
> eBPF doesn't have BPF_RET instruction and this restriction.
> It has BPF_EXIT insn which can appear anywhere in the program
> one or more times and it doesn't have to be last insn.

[1] https://lkml.org/lkml/2014/11/27/2

Fixes: e54bcde3 ("arm64: eBPF JIT compiler")
Acked-by: NAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: NZi Shen Lim <zlim.lnx@gmail.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
上级 e4f88d83
......@@ -60,7 +60,7 @@ struct jit_ctx {
const struct bpf_prog *prog;
int idx;
int tmp_used;
int body_offset;
int epilogue_offset;
int *offset;
u32 *image;
};
......@@ -130,8 +130,8 @@ static void jit_fill_hole(void *area, unsigned int size)
static inline int epilogue_offset(const struct jit_ctx *ctx)
{
int to = ctx->offset[ctx->prog->len - 1];
int from = ctx->idx - ctx->body_offset;
int to = ctx->epilogue_offset;
int from = ctx->idx;
return to - from;
}
......@@ -463,6 +463,8 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
}
/* function return */
case BPF_JMP | BPF_EXIT:
/* Optimization: when last instruction is EXIT,
simply fallthrough to epilogue. */
if (i == ctx->prog->len - 1)
break;
jmp_offset = epilogue_offset(ctx);
......@@ -685,11 +687,13 @@ void bpf_int_jit_compile(struct bpf_prog *prog)
/* 1. Initial fake pass to compute ctx->idx. */
/* Fake pass to fill in ctx->offset. */
/* Fake pass to fill in ctx->offset and ctx->tmp_used. */
if (build_body(&ctx))
goto out;
build_prologue(&ctx);
ctx.epilogue_offset = ctx.idx;
build_epilogue(&ctx);
/* Now we know the actual image size. */
......@@ -706,7 +710,6 @@ void bpf_int_jit_compile(struct bpf_prog *prog)
build_prologue(&ctx);
ctx.body_offset = ctx.idx;
if (build_body(&ctx)) {
bpf_jit_binary_free(header);
goto out;
......
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