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Date:   Mon, 11 Jan 2021 10:33:38 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     akpm@linux-foundation.org, jannh@google.com, jeffv@google.com,
        minchan@kernel.org, mhocko@suse.com, shakeelb@google.com,
        rientjes@google.com, edgararriaga@google.com, timmurray@google.com,
        linux-mm@kvack.org, selinux@vger.kernel.org,
        linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@android.com
Subject: Re: [PATCH v2 1/1] mm/madvise: replace ptrace attach requirement for
 process_madvise
Message-ID: <202101111033.2D03EA97@keescook>
References: <20210111170622.2613577-1-surenb@google.com>
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On Mon, Jan 11, 2021 at 09:06:22AM -0800, Suren Baghdasaryan 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.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook