Re: [PATCH bpf-next] bpf: Check return from set_memory_rox() and friends

[Christophe Leroy]

Le 19/02/2024 à 11:19, Simon Horman a écrit :
> On Sat, Feb 17, 2024 at 11:24:07AM +0100, Christophe Leroy wrote:
>> arch_protect_bpf_trampoline() and alloc_new_pack() call
>> set_memory_rox() which can fail, leading to unprotected memory.
>>
>> Take into account return from set_memory_XX() functions and add
>> __must_check flag to arch_protect_bpf_trampoline().
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> 
> ...
> 
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index ea6843be2616..23ce17da3bf7 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -898,23 +898,30 @@ static LIST_HEAD(pack_list);
>>   static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_insns)
>>   {
>>   	struct bpf_prog_pack *pack;
>> +	int err;
>>   
>>   	pack = kzalloc(struct_size(pack, bitmap, BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)),
>>   		       GFP_KERNEL);
>>   	if (!pack)
>>   		return NULL;
>>   	pack->ptr = bpf_jit_alloc_exec(BPF_PROG_PACK_SIZE);
>> -	if (!pack->ptr) {
>> -		kfree(pack);
>> -		return NULL;
>> -	}
>> +	if (!pack->ptr)
>> +		goto out;
>>   	bpf_fill_ill_insns(pack->ptr, BPF_PROG_PACK_SIZE);
>>   	bitmap_zero(pack->bitmap, BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE);
>>   	list_add_tail(&pack->list, &pack_list);
> 
> Hi Christophe,
> 
> Here pack is added to pack_list.
> 
>>   
>>   	set_vm_flush_reset_perms(pack->ptr);
>> -	set_memory_rox((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
>> +	err = set_memory_rox((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
>> +	if (err)
>> +		goto out_free;
> 
> But this unwind path doesn't appear to remove pack form pack_list.

Ah, thanks,

Indeed I wondered about it and ignored it as I mis-read pack_list as 
pack->list, thinking it would implicitely fly away when droping pack.

I'll send a v2 in a few days once more people have reviewed it.

Christophe