On Mon, Jan 11, 2021 at 5:22 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, 11 Jan 2021 09:06:22 -0800 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > 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). > > What we want is the ability for one process to influence another process > > in order to optimize performance across the entire system while leaving > > the security boundary intact. > > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ > > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata > > and CAP_SYS_NICE for influencing process performance. > > It would be useful to see the proposed manpage update. > > process_madvise() was released in 5.10, so this is a > non-backward-compatible change to a released kernel. > > I think it would be OK at this stage to feed this into 5.10.x with a > cc:stable and suitable words in the changelog explaining why we're > doing this. Sure, I will post another patchset that will include manpage update and will CC:stable. That's of course after Michal's concerns are addressed. Thanks! > > Alternatively we could retain PTRACE_MODE_ATTACH's behaviour and add > PTRACE_MODE_READ&CAP_SYS_NICE alongside that.
