linux-kernel - Re: [PATCH v2 bpf-next 5/7] x86/alternative: introduce text_poke

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Date:   Wed, 15 Dec 2021 10:17:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <song@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kernel-team@...com, x86@...nel.org
Subject: Re: [PATCH v2 bpf-next 5/7] x86/alternative: introduce text_poke_jit

On Tue, Dec 14, 2021 at 10:01:00PM -0800, Song Liu wrote:
> This will be used by BPF jit compiler to dump JITed binary to a RWX huge

OK, I read the actually allocator you use and the relevant code for this
patch and the above is a typo, you meant: RX. Those pages are most
definitely not writable.


> +void *text_poke_jit(void *addr, const void *opcode, size_t len)
> +{
> +	unsigned long start = (unsigned long)addr;
> +	size_t patched = 0;
> +
> +	if (WARN_ON_ONCE(core_kernel_text(start)))
> +		return NULL;
> +
> +	while (patched < len) {
> +		unsigned long ptr = start + patched;
> +		size_t s;
> +
> +		s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched);

Cute, should work.

> +
> +		__text_poke((void *)ptr, opcode + patched, s);
> +		patched += s;
> +	}
> +	return addr;
> +}