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From:   Florian Weimer <fweimer@redhat.com>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     akpm@linux-foundation.org, jannh@google.com, keescook@chromium.org,
        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 1/1] mm/madvise: replace ptrace attach requirement for
 process_madvise
References: <20210108205857.1471269-1-surenb@google.com>
Date:   Mon, 11 Jan 2021 11:20:01 +0100
In-Reply-To: <20210108205857.1471269-1-surenb@google.com> (Suren
        Baghdasaryan's message of "Fri, 8 Jan 2021 12:58:57 -0800")
Message-ID: <875z43rd0u.fsf@oldenburg2.str.redhat.com>
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* Suren Baghdasaryan:

> diff --git a/mm/madvise.c b/mm/madvise.c
> index 6a660858784b..c2d600386902 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
>  		goto release_task;
>  	}
>  
> -	mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
> +	/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
> +	mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
>  	if (IS_ERR_OR_NULL(mm)) {
>  		ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
>  		goto release_task;
>  	}

Shouldn't this depend on the requested behavior?  Several operations
directly result in observable changes, and go beyond performance tuning.

Thanks,
Florian
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