RE: [patch] x86, ptrace: require admin privileges for ptrace BTSextension

[Metzger, Markus T]

>-----Original Message-----
>From: stephane eranian [mailto:eranian@xxxxxxxxxxxxxx] 
>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@xxxxxxxxx> 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@xxxxxxx>
>> Signed-off-by: Markus Metzger <markus.t.metzger@xxxxxxxxx>
>> ---
>>
>> 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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Intel GmbH
Dornacher Strasse 1
85622 Feldkirchen/Muenchen Germany
Sitz der Gesellschaft: Feldkirchen bei Muenchen
Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer
Registergericht: Muenchen HRB 47456 Ust.-IdNr.
VAT Registration No.: DE129385895
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