Re: [PATCH] Documentation/tracing: Mention that RESET_ATTACK_MITIGATION can clear memory

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 26 Sep 2024 19:54:48 +0200
Hans de Goede <hdegoede@redhat.com> wrote:

> Hi,
> 
> On 26-Sep-24 7:01 PM, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt@goodmis.org>
> > 
> > At the 2024 Linux Plumbers Conference, I was talking with Hans de Goede
> > about the persistent buffer to display traces from previous boots. He
> > mentioned that UEFI can clear memory. In my own tests I have not seen
> > this. He later informed me that it requires the config option:
> > 
> >  CONFIG_RESET_ATTACK_MITIGATION
> > 
> > It appears that setting this will allow the memory to be cleared on boot
> > up, which will definitely clear out the trace of the previous boot.
> > 
> > Add this information under the trace_instance in kernel-parameters.txt
> > to let people know that this can cause issues.
> > 
> > Link: https://lore.kernel.org/all/20170825155019.6740-2-ard.biesheuvel@linaro.org/
> > 
> > Reported-by: Hans de Goede <hdegoede@redhat.com>
> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>  
> 
> Thanks, patch looks good to me:
> 
> Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Thanks,

And I forgot to send this to the Documentation maintainers :-p

Jon, could you take this? Do you need me to resend, or can you just pull it
from lore?

   https://lore.kernel.org/linux-trace-kernel/20240926130159.19e6d0e2@rorschach.local.home/

-- Steve


> 
> Regards,
> 
> Hans
> 
> 
> 
> > ---
> >  Documentation/admin-guide/kernel-parameters.txt | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index bb48ae24ae69..f9b79294f84a 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -6850,6 +6850,9 @@
> >  
> >  				reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq
> >  
> > +			Note, CONFIG_RESET_ATTACK_MITIGATION can force a memory reset on boot which
> > +			will clear any trace that was stored.
> > +
> >  			See also Documentation/trace/debugging.rst
> >  
> >