linux-kernel - RE: [patch] x86, ptrace: require admin privileges for ptrace BTS extension

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E0CC3B06E@irsmsx504.ger.corp.intel.com>
Date:	Mon, 22 Dec 2008 15:02:09 +0000
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	"eranian@...il.com" <eranian@...il.com>
CC:	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"roland@...hat.com" <roland@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mtk.manpages@...il.com" <mtk.manpages@...il.com>,
	"Villacis, Juan" <juan.villacis@...el.com>
Subject: RE: [patch] x86, ptrace: require admin privileges for ptrace BTS
 extension

>-----Original Message-----
>From: stephane eranian [mailto:eranian@...glemail.com] 
>Sent: Montag, 22. Dezember 2008 14:24
>To: Metzger, Markus T

>On Mon, Dec 22, 2008 at 1:02 PM, Markus Metzger
><markus.t.metzger@...el.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)?

Ingo requested this as a precaution.
We found a bug: the DS context pointer is not cleared on fork.
The bug is fixed in tip/master but the fix is considered too intrusive to be promoted that late.
The restriction will be removed once the fix is in.

regards,
markus.



>
>Thanks.
>
>>
>> Reported-by: Ingo Molnar <mingo@...e.hu>
>> Signed-off-by: Markus Metzger <markus.t.metzger@...el.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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