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Commit f324cda6 authored by Zi Shen Lim's avatar Zi Shen Lim Committed by Greg Kroah-Hartman
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arm64: bpf: lift restriction on last instruction 

commit 51c9fbb1b146f3336a93d398c439b6fbfe5ab489 upstream.

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: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarZi Shen Lim <zlim.lnx@gmail.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 516e433a

arch/arm64/net/bpf_jit_comp.c

+8 −5
Original line number Original line Diff line number Diff line
@@ -60,7 +60,7 @@ struct jit_ctx { 
	const struct bpf_prog *prog;

	const struct bpf_prog *prog;

	int idx;

	int idx;

	int tmp_used;

	int tmp_used;

	int body_offset;

	int epilogue_offset;

	int *offset;

	int *offset;

	u32 *image;

	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)

static inline int epilogue_offset(const struct jit_ctx *ctx)

{

{

	int to = ctx->offset[ctx->prog->len - 1];

	int to = ctx->epilogue_offset;

	int from = ctx->idx - ctx->body_offset;

	int from = ctx->idx;





	return to - from;

	return to - from;

}

}
@@ -463,6 +463,8 @@ emit_cond_jmp: 
	}

	}

	/* function return */

	/* function return */

	case BPF_JMP | BPF_EXIT:

	case BPF_JMP | BPF_EXIT:

		/* Optimization: when last instruction is EXIT,

		   simply fallthrough to epilogue. */

		if (i == ctx->prog->len - 1)

		if (i == ctx->prog->len - 1)

			break;

			break;

		jmp_offset = epilogue_offset(ctx);

		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. */

	/* 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))

	if (build_body(&ctx))

		goto out;

		goto out;





	build_prologue(&ctx);

	build_prologue(&ctx);



	ctx.epilogue_offset = ctx.idx;

	build_epilogue(&ctx);

	build_epilogue(&ctx);





	/* Now we know the actual image size. */

	/* Now we know the actual image size. */
@@ -706,7 +710,6 @@ void bpf_int_jit_compile(struct bpf_prog *prog) 




	build_prologue(&ctx);

	build_prologue(&ctx);





	ctx.body_offset = ctx.idx;

	if (build_body(&ctx)) {

	if (build_body(&ctx)) {

		bpf_jit_binary_free(header);

		bpf_jit_binary_free(header);

		goto out;

		goto out;