linux-kernel - Re: [PATCH 03/23] perf: Add ability to attach user level registers dump to sample

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120629075043.GD940@krava.brq.redhat.com>
Date:	Fri, 29 Jun 2012 09:50:43 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>, acme@...hat.com,
	mingo@...e.hu, paulus@...ba.org, cjashfor@...ux.vnet.ibm.com,
	gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com,
	robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 03/23] perf: Add ability to attach user level registers
 dump to sample

On Wed, Jun 27, 2012 at 05:30:05PM +0200, Frederic Weisbecker wrote:
> On Wed, Jun 27, 2012 at 05:25:29PM +0200, Peter Zijlstra wrote:
> > On Wed, 2012-06-27 at 17:24 +0200, Frederic Weisbecker wrote:
> > > On Wed, Jun 27, 2012 at 05:13:44PM +0200, Stephane Eranian wrote:
> > > > On Wed, Jun 27, 2012 at 5:11 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > > > > On Tue, Jun 19, 2012 at 05:47:54PM +0200, Jiri Olsa wrote:
> > > > >> @@ -4061,6 +4105,19 @@ void perf_prepare_sample(struct perf_event_header *header,
> > > > >>               }
> > > > >>               header->size += size;
> > > > >>       }
> > > > >> +
> > > > >> +     if (sample_type & PERF_SAMPLE_REGS_USER) {
> > > > >> +             /* regs dump available bool */
> > > > >> +             int size = sizeof(u64);
> > > > >> +
> > > > >> +             data->regs_user = perf_sample_regs_user(regs);
> > > > >> +             if (data->regs_user) {
> > > > >> +                     u64 mask = event->attr.sample_regs_user;
> > > > >> +                     size += hweight64(mask) * sizeof(u64);
> > > > >> +             }
> > > > >> +
> > > > >> +             header->size += size;
> > > > >
> > > > > We'll need to remove the 64 bits registers for compat tasks but other than
> > > > > that, it looks ok.
> > > > You cannot do this. You cannot remove register values from under the hood.
> > > > The only way the user has to parse the sample is the sample_regs_users bitmask.
> > > > You have to return 0 for those unexisting regs for compat tasks.
> > > 
> > > You mean fill unexisting reg values with 0? Yeah that works.
> > 
> > What does x32 look like? Is that still reported as a compat task? If so,
> > we should record all registers and not 0 out anything.
> 
> To make it simple, we could always use the x86-64 registers mask interface for everyone:
> native 32 bits kernel, compat 32 bits task, 64 bits everything. And we can't fill an x86-64
> value because we are dealing with a native/compat 32 task we just fill out the requested value
> with 0.
> 
> On post processing time, userspace can know if it's dealing with 32 bits task or not anyway, so
> it knows what to skip and what is relevant.

well, thats basically what we have now..

when the kernel is compiled for 32 bits, the bitmask allows to store:

ax, bx, cx, dx, si, di, bp, sp, ip, flags, cs, ds, es, fs, gs, ss

and when  kernel is compiled for 64 bits, the bitmask adds 64bit stuff:

ax, bx, cx, dx, si, di, bp, sp, ip, flags, cs, ds, es, fs, gs, ss
r8, r9, r10, r11, r12, r13, r14, r15


- 32 bits kernel is straightforward

- for 64 bits kernel we store whatever bitmask instructs to,
  regardless if we are in compat task or native 64,
  user space will deal with that in post processing


jirka
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/