Re: [PATCH v3 2/5] powerpc/bpf: implement bpf_arch_text_invalidate for bpf_prog_pack

[Hari Bathini <hbathini@linux.ibm.com>]

On 25/08/23 9:03 pm, Christophe Leroy wrote:
> 
> 
> Le 25/08/2023 à 17:18, Hari Bathini a écrit :
>> Implement bpf_arch_text_invalidate and use it to fill unused part of
>> the bpf_prog_pack with trap instructions when a BPF program is freed.
>>
>> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
>> ---
>>    arch/powerpc/net/bpf_jit_comp.c | 22 +++++++++++++++++++---
>>    1 file changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
>> index 170ebf8ac0f2..7cd4cf53d61c 100644
>> --- a/arch/powerpc/net/bpf_jit_comp.c
>> +++ b/arch/powerpc/net/bpf_jit_comp.c
>> @@ -30,7 +30,7 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
>>     * Patch 'len' bytes of instructions from opcode to addr, one instruction
>>     * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
>>     */
>> -static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
>> +static void *bpf_patch_instructions(void *addr, void *opcode, size_t len, bool fill_insn)
> 
> It's a pitty that you have to modify in patch 2 a function you have
> added in patch 1 of the same series. Can't you have it right from the
> begining ?
> 
>>    {
>>    	while (len > 0) {
>>    		ppc_inst_t insn = ppc_inst_read(opcode);
>> @@ -41,7 +41,8 @@ static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
>>    
>>    		len -= ilen;
>>    		addr = addr + ilen;
>> -		opcode = opcode + ilen;
>> +		if (!fill_insn)
>> +			opcode = opcode + ilen;
>>    	}
>>    
>>    	return addr;
>> @@ -307,7 +308,22 @@ void *bpf_arch_text_copy(void *dst, void *src, size_t len)
>>    		return ERR_PTR(-EINVAL);
>>    
>>    	mutex_lock(&text_mutex);
>> -	ret = bpf_patch_instructions(dst, src, len);
>> +	ret = bpf_patch_instructions(dst, src, len, false);
>> +	mutex_unlock(&text_mutex);
>> +
>> +	return ret;
>> +}
>> +
>> +int bpf_arch_text_invalidate(void *dst, size_t len)
>> +{
>> +	u32 insn = BREAKPOINT_INSTRUCTION;
>> +	int ret;
>> +
>> +	if (WARN_ON_ONCE(core_kernel_text((unsigned long)dst)))
>> +		return -EINVAL;
>> +
>> +	mutex_lock(&text_mutex);
>> +	ret = IS_ERR(bpf_patch_instructions(dst, &insn, len, true));
> 
> Why IS_ERR ?
> 
> As far as I understand from the weak definition in kernel/bpf/core.c,
> this function is supposed to return an error, not a bool.

My bad! Will fix that in the next revision.

- Hari