[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20130605133555.GE32700@dhcp-25-225.brq.redhat.com>
Date: Wed, 5 Jun 2013 15:35:55 +0200
From: Petr Matousek <pmatouse@...hat.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: eranian@...gle.com, ak@...ux.intel.com, security@...nel.org,
Marcus Meissner <meissner@...e.de>, oss-security@...ts.openwall.com
Subject: Re: CVE Request: More perf security fixes
On Wed, Jun 05, 2013 at 03:02:53PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 05, 2013 at 02:38:56PM +0200, Petr Matousek wrote:
> > On Wed, Jun 05, 2013 at 02:15:59PM +0200, Peter Zijlstra wrote:
> > > On Wed, Jun 05, 2013 at 02:10:54PM +0200, Petr Matousek wrote:
> > > > Hello, Peter.
> > > >
> > > > On Tue, Jun 04, 2013 at 05:53:16PM +0200, Marcus Meissner wrote:
> > > > > 1. Info leak (?) via PERF_SAMPLE_BRANCH_KERNEL
> > > > >
> > > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7cc23cd6c0c7d7f4bee057607e7ce01568925717
> > > > >
> > > > > commit 7cc23cd6c0c7d7f4bee057607e7ce01568925717
> > > > > Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > > > Date: Fri May 3 14:11:25 2013 +0200
> > > > >
> > > > > perf/x86/intel/lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL
> > > > >
> > > > > We should always have proper privileges when requesting kernel
> > > > > data.
> > > > >
> > > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > > > Cc: <stable@...nel.org>
> > > > > Cc: Andi Kleen <ak@...ux.intel.com>
> > > > > Cc: eranian@...gle.com
> > > > > Link: http://lkml.kernel.org/r/20130503121256.230745028@chello.nl
> > > > > [ Fix build error reported by fengguang.wu@...el.com, propagate error code back. ]
> > > > > Signed-off-by: Ingo Molnar <mingo@...nel.org>
> > > > > Link: http://lkml.kernel.org/n/tip-v0x9ky3ahzr6nm3c6ilwrili@git.kernel.org
> > > >
> > > > There is similar check in perf_copy_attr() which is called from
> > > > perf_event_open syscall --
> > > >
> > > > /* kernel level capture: check permissions */
> > > > if ((mask & PERF_SAMPLE_BRANCH_PERM_PLM)
> > > > && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> > > > return -EACCES;
> > > >
> > > > It seems to me that it covers PERF_SAMPLE_BRANCH_KERNEL as well. Am I
> > > > missing something?
> > > >
> > >
> > > I overlooked it, also its slightly broken. See the discussion at:
> > > https://lkml.org/lkml/2013/5/21/166
> >
> > Got it, thanks for the pointer. So it is safe to say there never was a
> > leak in this case (and thus no security issue worth CVE)?
>
> There was a leak, notice how Stephane's patch did a
> s/PERF_SAMPLE_BRANCH_PERM_PLM/PERF_SAMPLE_BRANCH_KERNEL/
PERF_SAMPLE_BRANCH_PERM_PLM is a superset of PERF_SAMPLE_BRANCH_KERNEL:
#define PERF_SAMPLE_BRANCH_PERM_PLM \
(PERF_SAMPLE_BRANCH_KERNEL |\
PERF_SAMPLE_BRANCH_HV)
> but also places
> the check _after_ we propagate the event PLM levels in the case none
> were LBR specific.
Assuming the leak does occur only when PERF_SAMPLE_BRANCH_KERNEL is set,
that does not matter:
/* kernel level capture: check permissions */
if ((mask & PERF_SAMPLE_BRANCH_PERM_PLM)
&& perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
return -EACCES;
^^^ this assures proper permission check if PERF_SAMPLE_BRANCH_KERNEL
is explicitly set
/* propagate priv level, when not set for branch */
if (!(mask & PERF_SAMPLE_BRANCH_PLM_ALL)) {
/* exclude_kernel checked on syscall entry */
if (!attr->exclude_kernel)
mask |= PERF_SAMPLE_BRANCH_KERNEL;
And following check in perf_event_open syscall assures the permission
are right for (!(mask & PERF_SAMPLE_BRANCH_PLM_ALL)) code:
if (!attr.exclude_kernel) {
if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
return -EACCES;
}
--
Petr Matousek / Red Hat Security Response Team
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
