Date: Thu, 3 Oct 2019 14:36:07 -0700 From: Kees Cook <keescook@...omium.org> To: Muni Sekhar <munisekharrms@...il.com> Cc: kernel-hardening@...ts.openwall.com Subject: Re: How to get the crash dump if system hangs? On Thu, Oct 03, 2019 at 10:18:48PM +0530, Muni Sekhar wrote: > Thanks a lot for letting me know about pstore, will try this option. > It will be helpful if you can share some pointers on 'how to enable > software ECC'? When I boot with pstore, I use a bunch of command line arguments to test all its feature: ramoops.mem_size=1048576 ramoops.ecc=1 ramoops.mem_address=0x440000000 ramoops.console_size=16384 ramoops.ftrace_size=16384 ramoops.pmsg_size=16384 ramoops.record_size=32768 but I'm using pmem driver to reserve the 1MB of memory at 0x440000000. To do a RAM reservation on a regular system, you'll need to do something like boot with: memmap=1M!1023M which says, reserve 1MB of memory at the 1023M offset. So this depends on how much physical memory you have, etc, but you'll be able to see the reservation after booting in /proc/iomem. e.g. for me, before: ... 00100000-bffd9fff : System RAM ... with memmap: ... 00100000-3fefffff : System RAM 3ff00000-3fffffff : Persistent Memory (legacy) 40000000-bffd9fff : System RAM ... So in that example, the address you'd want is 0x3ff00000 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 In dmesg you should see: [ 0.868818] pstore: Registered ramoops as persistent store backend [ 0.869713] ramoops: using 0x100000@...ff00000, ecc: 16 And if that address lines up with the "Persistent Memory (legacy)" line in /proc/iomem you should be good to go. Just mount /sys/fs/pstore and see if the console dump updates between warm boots, then try some cold boots, see if the ECC works, etc. Good luck! -- Kees Cook
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