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Message-ID: <7c86c4470812220523y7ccca8cag40f758393017cf7c@mail.gmail.com>
Date: Mon, 22 Dec 2008 14:23:38 +0100
From: "stephane eranian" <eranian@googlemail.com>
Reply-To: eranian@gmail.com
To: "Markus Metzger" <markus.t.metzger@intel.com>
Subject: Re: [patch] x86, ptrace: require admin privileges for ptrace BTS extension
Cc: hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@elte.hu,
       tglx@linutronix.de, markus.t.metzger@gmail.com, roland@redhat.com,
       akpm@linux-foundation.org, mtk.manpages@gmail.com,
       juan.villacis@intel.com
In-Reply-To: <20081222130218.A31747@sedona.ch.intel.com>
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Markus,

On Mon, Dec 22, 2008 at 1:02 PM, Markus Metzger
<markus.t.metzger@intel.com> wrote:
> Require admin privileges for ptrace BTS extension.
>
Can you explain the motivations for this?

I thought the BTS extension was a per-process functionality.
So how come I can debug and single step my process without
admin privilege and I cannot capture its own branches. Does this
have to do with user vs. kernel execution of the proces (BTS
captures everything if I recall)?

Thanks.

>
> Reported-by: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
> ---
>
> Index: gits/arch/x86/kernel/ptrace.c
> ===================================================================
> --- gits.orig/arch/x86/kernel/ptrace.c  2008-12-22 09:09:25.000000000 +0100
> +++ gits/arch/x86/kernel/ptrace.c       2008-12-22 11:03:01.000000000 +0100
> @@ -21,6 +21,7 @@
>  #include <linux/audit.h>
>  #include <linux/seccomp.h>
>  #include <linux/signal.h>
> +#include <linux/capability.h>
>
>  #include <asm/uaccess.h>
>  #include <asm/pgtable.h>
> @@ -742,6 +743,10 @@
>        struct ptrace_bts_config cfg;
>        int error = 0;
>
> +       error = -EPERM;
> +       if (!capable(CAP_SYS_ADMIN))
> +               goto errout;
> +
>        error = -EOPNOTSUPP;
>        if (!bts_cfg.sizeof_bts)
>                goto errout;
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