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Date:   Thu, 10 Aug 2023 16:50:56 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Vijay Balakrishna <vijayb@linux.microsoft.com>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        John Ogness <john.ogness@linutronix.de>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Anton Vorontsov <anton@enomsg.org>,
        linux-kernel@vger.kernel.org
Subject: Re: pstore/ram: printk: NULL characters in pstore ramoops area
Message-ID: <202308101649.337F4D8@keescook>
References: <f28990eb-03bc-2259-54d0-9f2254abfe62@linux.microsoft.com>
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 <0220f601-14f8-1dda-f057-73a608fbe62b@linux.microsoft.com>
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On Thu, Aug 10, 2023 at 04:32:58PM -0700, Vijay Balakrishna wrote:
> 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@vijay-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|

Can you share the .config you're building with? And what are you using
to trigger an Oops? I will see if I can reproduce this...

-- 
Kees Cook