Re: [PATCH RFC v2] Randomized slab caches for kmalloc()

[Gong Ruiqi]

On 2023/05/11 22:54, Alexander Lobakin wrote:

[...]

>> @@ -777,12 +783,44 @@ EXPORT_SYMBOL(kmalloc_size_roundup);
>>  #define KMALLOC_RCL_NAME(sz)
>>  #endif
>>  
>> +#ifdef CONFIG_RANDOM_KMALLOC_CACHES
>> +#define __KMALLOC_RANDOM_CONCAT(a, b, c) a ## b ## c
>> +#define KMALLOC_RANDOM_NAME(N, sz) __KMALLOC_RANDOM_CONCAT(KMALLOC_RANDOM_, N, _NAME)(sz)
>> +#if CONFIG_RANDOM_KMALLOC_CACHES_BITS >= 1
>> +#define KMALLOC_RANDOM_1_NAME(sz)                             .name[KMALLOC_RANDOM_START +  0] = "kmalloc-random-01-" #sz,
>> +#define KMALLOC_RANDOM_2_NAME(sz)  KMALLOC_RANDOM_1_NAME(sz)  .name[KMALLOC_RANDOM_START +  1] = "kmalloc-random-02-" #sz,
>> +#endif
>> +#if CONFIG_RANDOM_KMALLOC_CACHES_BITS >= 2
>> +#define KMALLOC_RANDOM_3_NAME(sz)  KMALLOC_RANDOM_2_NAME(sz)  .name[KMALLOC_RANDOM_START +  2] = "kmalloc-random-03-" #sz,
>> +#define KMALLOC_RANDOM_4_NAME(sz)  KMALLOC_RANDOM_3_NAME(sz)  .name[KMALLOC_RANDOM_START +  3] = "kmalloc-random-04-" #sz,
>> +#endif
>> +#if CONFIG_RANDOM_KMALLOC_CACHES_BITS >= 3
>> +#define KMALLOC_RANDOM_5_NAME(sz)  KMALLOC_RANDOM_4_NAME(sz)  .name[KMALLOC_RANDOM_START +  4] = "kmalloc-random-05-" #sz,
>> +#define KMALLOC_RANDOM_6_NAME(sz)  KMALLOC_RANDOM_5_NAME(sz)  .name[KMALLOC_RANDOM_START +  5] = "kmalloc-random-06-" #sz,
>> +#define KMALLOC_RANDOM_7_NAME(sz)  KMALLOC_RANDOM_6_NAME(sz)  .name[KMALLOC_RANDOM_START +  6] = "kmalloc-random-07-" #sz,
>> +#define KMALLOC_RANDOM_8_NAME(sz)  KMALLOC_RANDOM_7_NAME(sz)  .name[KMALLOC_RANDOM_START +  7] = "kmalloc-random-08-" #sz,
>> +#endif
>> +#if CONFIG_RANDOM_KMALLOC_CACHES_BITS >= 4
>> +#define KMALLOC_RANDOM_9_NAME(sz)  KMALLOC_RANDOM_8_NAME(sz)  .name[KMALLOC_RANDOM_START +  8] = "kmalloc-random-09-" #sz,
>> +#define KMALLOC_RANDOM_10_NAME(sz) KMALLOC_RANDOM_9_NAME(sz)  .name[KMALLOC_RANDOM_START +  9] = "kmalloc-random-10-" #sz,
>> +#define KMALLOC_RANDOM_11_NAME(sz) KMALLOC_RANDOM_10_NAME(sz) .name[KMALLOC_RANDOM_START + 10] = "kmalloc-random-11-" #sz,
>> +#define KMALLOC_RANDOM_12_NAME(sz) KMALLOC_RANDOM_11_NAME(sz) .name[KMALLOC_RANDOM_START + 11] = "kmalloc-random-12-" #sz,
>> +#define KMALLOC_RANDOM_13_NAME(sz) KMALLOC_RANDOM_12_NAME(sz) .name[KMALLOC_RANDOM_START + 12] = "kmalloc-random-13-" #sz,
>> +#define KMALLOC_RANDOM_14_NAME(sz) KMALLOC_RANDOM_13_NAME(sz) .name[KMALLOC_RANDOM_START + 13] = "kmalloc-random-14-" #sz,
>> +#define KMALLOC_RANDOM_15_NAME(sz) KMALLOC_RANDOM_14_NAME(sz) .name[KMALLOC_RANDOM_START + 14] = "kmalloc-random-15-" #sz,
>> +#define KMALLOC_RANDOM_16_NAME(sz) KMALLOC_RANDOM_15_NAME(sz) .name[KMALLOC_RANDOM_START + 15] = "kmalloc-random-16-" #sz,
> 
> This all can be compressed. Only two things are variables here, so
> 
> #define KMALLOC_RANDOM_N_NAME(cur, prev, sz)	\
> 	KMALLOC_RANDOM_##prev##_NAME(sz),	\	
> 	.name[KMALLOC_RANDOM_START + prev] =	\
> 		"kmalloc-random-##cur##-" #sz
> 
> #define KMALLOC_RANDOM_16_NAME(sz) KMALLOC_RANDOM_N_NAME(16, 15, sz)
> 

I tried this way of implementation but it didn't work: it did not
propagate from 16 to 1, but stopped in the middle. I think it's because
the macro is somehow (indirectly) self-referential and the preprocessor
won't expand it. Check this for more info:

https://gcc.gnu.org/onlinedocs/cpp/Self-Referential-Macros.html

> Also I'd rather not put commas ',' at the end of each macro, they're
> usually put outside where the macro is used.

It seems here we have to put commas at the end. Not only it's to align
with how KMALLOC_{RCL,CGROUP,DMA}_NAME are implemented, but also
otherwise the expansion of INIT_KMALLOC_INFO would in some cases be like:

{
	.name[KMALLOC_NORMAL]  = "kmalloc-" #__short_size,
	, // an empty entry with a comma
}

which would cause compilation error in kmalloc_info[]'s initialization.

>> +#endif
>> +#else // CONFIG_RANDOM_KMALLOC_CACHES
>> +#define KMALLOC_RANDOM_NAME(N, sz)
>> +#endif
>> +
>>  #define INIT_KMALLOC_INFO(__size, __short_size)			\
>>  {								\
>>  	.name[KMALLOC_NORMAL]  = "kmalloc-" #__short_size,	\
>>  	KMALLOC_RCL_NAME(__short_size)				\
>>  	KMALLOC_CGROUP_NAME(__short_size)			\
>>  	KMALLOC_DMA_NAME(__short_size)				\
>> +	KMALLOC_RANDOM_NAME(CONFIG_RANDOM_KMALLOC_CACHES_NR, __short_size)	\
> 
> Can't those names be __initconst and here you'd just do one loop from 1
> to KMALLOC_CACHES_NR, which would assign names? I'm not sure compilers
> will expand that one to a compile-time constant and assigning 69
> different string pointers per one kmalloc size is a bit of a waste to me.

I'm not sure if I understand the question correctly, but I believe these
names have been __initconst since kmalloc_info[] is already marked with
it. Please let me know if it doesn't answer your question.

>>  	.size = __size,						\
>>  }
>>  
>> @@ -878,6 +916,11 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
>>  		flags |= SLAB_CACHE_DMA;
>>  	}
>>  
>> +#ifdef CONFIG_RANDOM_KMALLOC_CACHES
>> +	if (type >= KMALLOC_RANDOM_START && type <= KMALLOC_RANDOM_END)
>> +		flags |= SLAB_RANDOMSLAB;
>> +#endif
>> +
>>  	kmalloc_caches[type][idx] = create_kmalloc_cache(
>>  					kmalloc_info[idx].name[type],
>>  					kmalloc_info[idx].size, flags, 0,
>> @@ -904,7 +947,7 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>>  	/*
>>  	 * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined
>>  	 */
>> -	for (type = KMALLOC_NORMAL; type < NR_KMALLOC_TYPES; type++) {
>> +	for (type = KMALLOC_RANDOM_START; type < NR_KMALLOC_TYPES; type++) {
> 
> Can't we just define something like __KMALLOC_TYPE_START at the
> beginning of the enum to not search for all such places each time
> something new is added?

Yeah I'm okay with this. Before I apply this change I would like to know
more opinions (especially from the maintainers) about it.

> 
>>  		for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
>>  			if (!kmalloc_caches[type][i])
>>  				new_kmalloc_cache(i, type, flags);
>> @@ -922,6 +965,9 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>>  				new_kmalloc_cache(2, type, flags);
>>  		}
>>  	}
>> +#ifdef CONFIG_RANDOM_KMALLOC_CACHES
>> +	random_kmalloc_seed = get_random_u64();
>> +#endif
>>  
>>  	/* Kmalloc array is now usable */
>>  	slab_state = UP;
>> @@ -957,7 +1003,7 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
>>  		return ret;
>>  	}
>>  
>> -	s = kmalloc_slab(size, flags);
>> +	s = kmalloc_slab(size, flags, caller);
>>  
>>  	if (unlikely(ZERO_OR_NULL_PTR(s)))
>>  		return s;
> 
> Thanks,
> Olek