Re: [PATCH bpf-next v7 1/2] arm64: patching: implement text_poke API

[Puranjay Mohan]

Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> writes:

> On 1/25/2024 9:31 PM, Puranjay Mohan wrote:
>> The text_poke API is used to implement functions like memcpy() and
>> memset() for instruction memory (RO+X). The implementation is similar to
>> the x86 version.
>> 
>> This will be used by the BPF JIT to write and modify BPF programs. There
>> could be more users of this in the future.
>> 
>> Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
>> ---
>>   arch/arm64/include/asm/patching.h |  2 +
>>   arch/arm64/kernel/patching.c      | 80 +++++++++++++++++++++++++++++++
>>   2 files changed, 82 insertions(+)
>> 
>> diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
>> index 68908b82b168..587bdb91ab7a 100644
>> --- a/arch/arm64/include/asm/patching.h
>> +++ b/arch/arm64/include/asm/patching.h
>> @@ -8,6 +8,8 @@ int aarch64_insn_read(void *addr, u32 *insnp);
>>   int aarch64_insn_write(void *addr, u32 insn);
>>   
>>   int aarch64_insn_write_literal_u64(void *addr, u64 val);
>> +void *aarch64_insn_set(void *dst, u32 insn, size_t len);
>> +void *aarch64_insn_copy(void *dst, void *src, size_t len);
>>   
>>   int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
>>   int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
>> diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
>> index b4835f6d594b..5c2d34d890cf 100644
>> --- a/arch/arm64/kernel/patching.c
>> +++ b/arch/arm64/kernel/patching.c
>> @@ -105,6 +105,86 @@ noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
>>   	return ret;
>>   }
>>   
>> +typedef void text_poke_f(void *dst, void *src, size_t patched, size_t len);
>> +
>
> How about removing the argument 'patched' and passing 'src + patched' as the
> second argument?
>

The memcpy() function needs 'src + patched' but the memset() needs only the 'src' and
will ignore the 'patched'. To make these implementations generic, I pass
both src and patched separately and allow the implementation of
text_poke_f() to use them.

If you think there is a better way to implement this then I would love
to use that.

>> +static void *__text_poke(text_poke_f func, void *addr, void *src, size_t len)
>> +{
>> +	unsigned long flags;
>> +	size_t patched = 0;
>> +	size_t size;
>> +	void *waddr;
>> +	void *ptr;
>> +	int ret;
>> +
>> +	raw_spin_lock_irqsave(&patch_lock, flags);
>> +
>> +	while (patched < len) {
>> +		ptr = addr + patched;
>> +		size = min_t(size_t, PAGE_SIZE - offset_in_page(ptr),
>> +			     len - patched);
>> +
>> +		waddr = patch_map(ptr, FIX_TEXT_POKE0);
>> +		func(waddr, src, patched, size);
>> +		patch_unmap(FIX_TEXT_POKE0);
>> +
>> +		if (ret < 0) {
>
> Where is 'ret' assigned?
>

Will remove the error check in next version as func() is of type void
and this error check was left from the previous version.

Thanks,
Puranjay