linux-kernel - Re: [PATCH 2/2] x86/cfi,bpf: Fix BPF JIT call

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Message-ID: <20231120155936.GY8262@noisy.programming.kicks-ass.net>
Date:   Mon, 20 Nov 2023 16:59:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, tglx@...utronix.de, mingo@...hat.com,
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        ndesaulniers@...gle.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
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        mark.rutland@....com
Subject: Re: [PATCH 2/2] x86/cfi,bpf: Fix BPF JIT call

On Mon, Nov 20, 2023 at 03:46:44PM +0100, Peter Zijlstra wrote:

> @@ -2935,9 +3009,9 @@ struct bpf_prog *bpf_int_jit_compile(str
>  			jit_data->header = header;
>  			jit_data->rw_header = rw_header;
>  		}
> -		prog->bpf_func = (void *)image;
> +		prog->bpf_func = (void *)image + ctx.prog_offset;
>  		prog->jited = 1;
> -		prog->jited_len = proglen;
> +		prog->jited_len = proglen - ctx.prog_offset; // XXX?
>  	} else {
>  		prog = orig_prog;
>  	}


Note the XXX there, I wasn't sure what the desired semantics of proglen
was. As implemented it is the length from where bpf_func points to the
end, not including the pre-preamble -- as indicated by offset.