Re: [PATCH v2 bpf-next 5/7] x86/alternative: introduce text_poke_jit

[Song Liu <songliubraving@fb.com>]

> On Dec 15, 2021, at 1:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> 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.

Yeah, it was a typo. I meant to say ROX. 

Thanks,
Song
> 
> 
>> +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;
>> +}