On 6/27/2018 1:18 PM, Richard Weinberger wrote:
Am Mittwoch, 27. Juni 2018, 15:12:48 CEST schrieb Michal Hocko:
On Wed 27-06-18 13:29:05, Richard Weinberger wrote:
On Wed, Jun 27, 2018 at 11:34 AM, Jefferson Carpenter
<[email protected]> wrote:
Is there a way for a user process to mark memory as 'sensitive' or
'non-sensitive' when it is allocated? That could allow it not to have to be
zeroed before being allocated to another process.
Isn't this what we have Meltdown and Spectre for? ;-)
No, memory from the kernel is always zeroed.
libc offers malloc() and calloc() for this purpose.
Interesting. Let's say
Process 1:
free(use_memory(malloc(1024)));
Then Process 2:
malloc(1024);
The physical RAM used to service Process 2's malloc call has to be
zeroed to prevent it from leaking data from Process 1. However, if
Process 1 could mark that memory as non-sensitive, then it would not
have to be zeroed, saving the time it takes to do that. However, this
would require at least a bit per memory page, so maybe it's not worth it.
Well, except for the weird MAP_UNINITIALIZED. Anyway agreed that this is
a bad idea and the flag should have never been merged. I've just
mentioned it for completness.
Oh, I forgot about the crazy nommu world. :-)
Thanks,
//richard
