On Tue 12-01-21 10:12:03, Suren Baghdasaryan wrote:

On Mon, Jan 11, 2021 at 11:46 PM Michal Hocko [off-list ref] wrote:

quoted

On Mon 11-01-21 09:06:22, Suren Baghdasaryan wrote:

quoted

process_madvise currently requires ptrace attach capability.
PTRACE_MODE_ATTACH gives one process complete control over another
process. It effectively removes the security boundary between the
two processes (in one direction). Granting ptrace attach capability
even to a system process is considered dangerous since it creates an
attack surface. This severely limits the usage of this API.
The operations process_madvise can perform do not affect the correctness
of the operation of the target process; they only affect where the data
is physically located (and therefore, how fast it can be accessed).

Yes it doesn't influence the correctness but it is still a very
sensitive operation because it can allow a targeted side channel timing
attacks so we should be really careful.

Sorry, I missed this comment in my answer. Possibility of affecting
the target's performance including side channel attack is why we
require CAP_SYS_NICE.

OK. It would be really good to document that in the man page. From the
current wording it seems we already rely on this cap for migration on a
remote process which is not the same thing but it roughly falls into the
similar category.
-- 
Michal Hocko
SUSE Labs