[PATCHv3] malloc: Make sure tcache_key is odd enough

[Cupertino Miranda]

Hi Wilco,


On 04-08-2025 11:12, Wilco Dijkstra wrote:
> Hi Cupertino,
> 
>> In order to avoid having tcache_key repeated through memory, why don't
>> we mangle it as well with, maybe not exactly as in PROTECT_PTR, however
>> using the location of chunk. A XOR perhaps ?
>>
>> I don't think it would have such a huge performance impact on the
>> overhaul execution time.
> 
> What problem would that solve? 
Patch commit message says:
"We want tcache_key not to be a commonly-occurring value in memory"

The detection of double-free in tcache is
> already quite limited. Using many different "keys" would only increase
> collisions with user data (which is what we are trying to avoid with this patch).
Probability of collision even mangling the value does not change.

Anyway, I thought the purpose was to make it harder to identify where 
the linked lists are in memory, reducing the number of repeated 
occurrences of the key.

Cheers,
Cupertino

> 
> Cheers,
> Wilco