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Thu, 26 Sep 2024 10:54:51 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHgJ2ce8we4Rd7DeLh3WEv+xfrahHxGE4lyf2Nkn1gqk5KwScN7/aCChIQ2CyyjKxqasmeoQQ== X-Received: by 2002:a17:907:1b96:b0:a93:ae71:994c with SMTP id a640c23a62f3a-a93c4aa6c84mr20386166b.57.1727373291119; Thu, 26 Sep 2024 10:54:51 -0700 (PDT) Received: from [10.100.0.2] ([94.101.114.121]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a93c297bcccsm22614166b.173.2024.09.26.10.54.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Sep 2024 10:54:50 -0700 (PDT) Message-ID: Date: Thu, 26 Sep 2024 19:54:48 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Documentation/tracing: Mention that RESET_ATTACK_MITIGATION can clear memory To: Steven Rostedt , LKML , Linux trace kernel Cc: Masami Hiramatsu , Mathieu Desnoyers , Mike Rapoport , Kees Cook , Ard Biesheuvel References: <20240926130159.19e6d0e2@rorschach.local.home> Content-Language: en-US, nl From: Hans de Goede In-Reply-To: <20240926130159.19e6d0e2@rorschach.local.home> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 26-Sep-24 7:01 PM, Steven Rostedt wrote: > 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@linaro.org/ > > Reported-by: Hans de Goede > Signed-off-by: Steven Rostedt (Google) Thanks, patch looks good to me: Reviewed-by: Hans de Goede 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 > >