Date: Thu, 10 Oct 2019 22:45:21 +0530 From: Muni Sekhar <munisekharrms@...il.com> To: Kees Cook <keescook@...omium.org> Cc: kernel-hardening@...ts.openwall.com Subject: Re: How to get the crash dump if system hangs? On Thu, Oct 10, 2019 at 10:26 PM Kees Cook <keescook@...omium.org> wrote: > > On Thu, Oct 10, 2019 at 09:19:26PM +0530, Muni Sekhar wrote: > > Later I booted with “memmap=1M!1023M ramoops.mem_size=1048576 > > ramoops.ecc=1 ramoops.mem_address=0x3ff00000 > > ramoops.console_size=16384 ramoops.ftrace_size=16384 > > ramoops.pmsg_size=16384 ramoops.record_size=32768 ramoops.mem_type=1 > > ramoops.dump_oops=1” > > > > After reboot, In dmesg I see the following lines: > > > > [ 0.373084] pstore: Registered ramoops as persistent store backend > > [ 0.373266] ramoops: attached 0x100000@...ff00000, ecc: 16/0 > > > > # cat /proc/iomem | grep "System RAM" > > 00001000-0009d7ff : System RAM > > 00100000-1fffffff : System RAM > > 20100000-3fefffff : System RAM > > 3ff00000-3fffffff : Persistent RAM > > 40000000-b937dfff : System RAM > > b9ba6000-b9ba6fff : System RAM > > b9be9000-b9d5dfff : System RAM > > b9ffa000-b9ffffff : System RAM > > 100000000-13fffffff : System RAM > > > > I noticed Persistent RAM, not Persistent Memory (legacy). What is the > > difference between these two? > > I think this might just be a difference is kernel versions and the > string reported here. As long as it's not "System RAM" it should be > available for pstore. > > > I could not find any file in /sys/fs/pstore after warm boot. Even > > tried to trigger the crash by running “echo c > /proc/sysrq-trigger” > > and then rebooted the system manually. After system boots up, I could > > not find dmesg-ramoops-N file in /sys/fs/pstore, even I could not find > > any file in /sys/fs/pstore directory. > > > > Am I missing anything? > > Silly question: has the pstore filesystem been mounted there? Yes, pstore is mounted. # mount | grep pstore pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime) > > $ mount | grep pstore > pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime) > > If so, try a warm reboot and you should have at least the prior boot's > console output in /sys/fs/pstore/console-ramoops-0 I'm using Ubuntu distro, ran "reboot" command but after reboot console-ramoops-0 is not present in /sys/fs/pstore > > If you don't, I'm not sure what's happening. You may want to try a newer > kernel (I see you've also go the old ramoops dmesg reporting about ecc.) > > Here's my dmesg... > > # dmesg | egrep -i 'pstore|ramoops' > ... > [ 1.004376] ramoops: using module parameters > [ 1.010837] ramoops: uncorrectable error in header > [ 1.163014] printk: console [pstore-1] enabled > [ 1.164476] pstore: Registered ramoops as persistent store backend > [ 1.165028] ramoops: using 0x100000@...40000000, ecc: 16 > [ 4.610229] pstore: Using crash dump compression: deflate > Here is my dmesg: # dmesg | egrep -i 'pstore|ramoops' [ 0.274931] ramoops: using module parameters [ 0.369885] console [pstore-1] enabled [ 0.372306] pstore: Registered ramoops as persistent store backend [ 0.372504] ramoops: attached 0x100000@...ff00000, ecc: 16/0 > If a warm boot works and cold boot doesn't, then it looks like your > hardware wipes enough of RAM (or loses refresh for long enough) that > even the ECC can't repair it, in which case pstore isn't going to work. > :( > > -- > Kees Cook -- Thanks, Sekhar
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