Re: [PATCH bpf-next v3 3/6] bpf: Disallow !kprobe_write_ctx progs tail-calling kprobe_write_ctx progs

[bot+bpf-ci]

> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c

[ ... ]

> +	switch (match) {
> +	case BPF_MAP_OWNER_MATCH_FOR_INIT:
> +		if (owner->kprobe_write_ctx != aux->kprobe_write_ctx)
> +			return false;
> +		break;
> +
> +	case BPF_MAP_OWNER_MATCH_FOR_UPDATE:
> +		if (!owner->kprobe_write_ctx && aux->kprobe_write_ctx)
> +			return false;
> +		break;
> +	}

In the v1 review, Alexei Starovoitov asked for strict conformance
both ways rather than one-directional validation:

    "Don't be fancy. Require strict conformance both ways
    in *all* patches."

https://lore.kernel.org/bpf/CAADnVQ+-V0-1i8_+CYpK7G0CnV-2n8e9Szv43yM3Az197eL_0A@xxxxxxxxxxxxxx/

The BPF_MAP_OWNER_MATCH_FOR_UPDATE case still uses one-directional
matching, rejecting only !owner->kprobe_write_ctx && aux->kprobe_write_ctx
but allowing the reverse.  Was this an intentional design choice, and
if so, should the changelog note the disagreement?


---
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