From nobody Thu Nov 28 22:46:08 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5AC1A1C6B4; Thu, 26 Sep 2024 17:02:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727370122; cv=none; b=dQb15c0E7Z/fkG7ILtR7Hc07KrQJNo2ESF4lYmGMesIR5H9HtvOFBfmX8DSydQPh0KTvj1Uw9guOzjad5Itd2Y4r3X2ioI37obl5aDkXfuMhjIe7K6FsBCL3kNGAs3ALS06gaG/oIebsSSb7IuVr6aQsarBkAB2P+jYD4P0PH1E= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727370122; c=relaxed/simple; bh=K9C9IfIihUP2RQiCo+rWgpc2wkCABq/E2CmKe9wU09U=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type; b=WoKL9ICh50gcuhjDHydFst1OdKmk0qSY6oG2bNGFrslgFJsVTkSCx3QxUpDTkjzmrPH6nDyPXjrHQa7Ef4OoLX7Q07IE2GrD/6/pm4ixmF1leB471tHF1gFktaGbM4fJX4IyyCrR2WCuxJHj77wjyT+QTB1iF6ogHhktMqZiiwk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30B8BC4CEC5; Thu, 26 Sep 2024 17:02:01 +0000 (UTC) Date: Thu, 26 Sep 2024 13:01:59 -0400 From: Steven Rostedt To: LKML , Linux trace kernel Cc: Masami Hiramatsu , Mathieu Desnoyers , Mike Rapoport , Kees Cook , Hans de Goede , Ard Biesheuvel Subject: [PATCH] Documentation/tracing: Mention that RESET_ATTACK_MITIGATION can clear memory Message-ID: <20240926130159.19e6d0e2@rorschach.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Steven Rostedt 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@lina= ro.org/ Reported-by: Hans de Goede Signed-off-by: Steven Rostedt (Google) Acked-by: Ard Biesheuvel Reviewed-by: Hans de Goede --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ 1 file changed, 3 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/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 @@ =20 reserve_mem=3D12M:4096:trace trace_instance=3Dboot_map^traceoff^tracep= rintk@trace,sched,irq =20 + Note, CONFIG_RESET_ATTACK_MITIGATION can force a memory reset on boot w= hich + will clear any trace that was stored. + See also Documentation/trace/debugging.rst =20 =20 --=20 2.45.2