On Thu, 26 Sep 2024 19:54:48 +0200
Hans de Goede [off-list ref] wrote:

Hi,

On 26-Sep-24 7:01 PM, Steven Rostedt wrote:

quoted

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/ (local)

Reported-by: Hans de Goede <redacted>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>  

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <redacted>

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/ (local)

-- Steve

Regards,

Hans

quoted

---
 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