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Date: Tue, 12 Jan 2021 09:36:18 -0800 From: Suren Baghdasaryan <surenb@...gle.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>, Jeffrey Vander Stoep <jeffv@...gle.com>, Minchan Kim <minchan@...nel.org>, Michal Hocko <mhocko@...e.com>, Shakeel Butt <shakeelb@...gle.com>, David Rientjes <rientjes@...gle.com>, Edgar Arriaga GarcĂa <edgararriaga@...gle.com>, Tim Murray <timmurray@...gle.com>, linux-mm <linux-mm@...ck.org>, selinux@...r.kernel.org, Linux API <linux-api@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, kernel-team <kernel-team@...roid.com> Subject: Re: [PATCH v2 1/1] mm/madvise: replace ptrace attach requirement for process_madvise On Mon, Jan 11, 2021 at 5:22 PM Andrew Morton <akpm@...ux-foundation.org> wrote: > > On Mon, 11 Jan 2021 09:06:22 -0800 Suren Baghdasaryan <surenb@...gle.com> 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.
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