linux-kernel - Re: pstore/ram: printk: NULL characters in pstore ramoops area

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Message-ID: <0220f601-14f8-1dda-f057-73a608fbe62b@linux.microsoft.com>
Date:   Thu, 10 Aug 2023 16:32:58 -0700
From:   Vijay Balakrishna <vijayb@...ux.microsoft.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Anton Vorontsov <anton@...msg.org>,
        linux-kernel@...r.kernel.org
Subject: Re: pstore/ram: printk: NULL characters in pstore ramoops area

On 8/4/23 00:59, Kees Cook wrote:
> Is the issue present in modern kernels?

Yes, the issue present in mainline kernel, I can repro on a x86_64 VM with v6.5.0-rc5 kernel.

$ uname -a
Linux vijay-vm3 6.5.0-rc5-ramoops #10 SMP PREEMPT_DYNAMIC Thu Aug 10 17:24:39 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-6.5.0-rc5-ramoops root=UUID=xx ro mem=8188M ramoops.mem_address=0x2BFC00000 ramoops.mem_size=0x400000 ramoops.max_reason=5 ramoops.record_size=0x80000 console=tty1 console=ttyS0 earlyprintk=ttyS0 rootdelay=300

(excerpt from /var/lib/systemd/pstore/dmesg-ramoops-0 after warm reboot)
<5>[    0.000000] Linux version 6.5.0-rc5-ramoops (vijay@...ay-vm1) (gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #10 SMP PREEMPT_DYNAMIC Thu Aug 10 17:24:39 UTC 2023
..
<6>[    0.463984] Calibrating delay loop (skipped), value calculated using timer frequency.. ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@

(hex dump output)

00003160  61 6c 63 75 6c 61 74 65  64 20 75 73 69 6e 67 20  |alculated using |
00003170  74 69 6d 65 72 20 66 72  65 71 75 65 6e 63 79 2e  |timer frequency.|
00003180  2e 20 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |. ..............|
00003190  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000031a0  00 0a 3c 36 3e 5b 20 20  20 20 30 2e 34 36 37 39  |..<6>[    0.4679|