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From:   Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Date:   Wed, 5 Feb 2020 20:07:44 +0900
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        lijiang <lijiang@redhat.com>, Petr Mladek <pmladek@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrea Parri <parri.andrea@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] printk: replace ringbuffer
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 <20200205050204.GI41358@google.com>
 <88827ae2-7af5-347b-29fb-cffb94350f8f@redhat.com>
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On (20/02/05 10:00), John Ogness wrote:
> On 2020-02-05, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> >>>> So there is a General protection fault. That's the type of a
> >>>> problem that kills the boot for me as well (different backtrace,
> >>>> tho).
> >>> 
> >>> Do you have CONFIG_RELOCATABLE and CONFIG_RANDOMIZE_BASE (KASLR)
> >>> enabled?
> >> 
> >> Yes. These two options are enabled.
> >> 
> >> CONFIG_RELOCATABLE=y
> >> CONFIG_RANDOMIZE_BASE=y
> >
> > So KASLR kills the boot for me. So does KASAN.
> 
> Sergey, thanks for looking into this already!
> 

So I hacked the system a bit.

3BUG: KASAN: wild-memory-access in copy_data+0x129/0x220>
3Write of size 4 at addr 5a5a5a5a5a5a5a5a by task cat/474>
Call Trace:>
 dump_stack+0x76/0xa0>
 ? copy_data+0x129/0x220>
 __kasan_report.cold+0x5/0x3b>
 ? get_page_from_freelist+0x1224/0x1490>
 ? copy_data+0x129/0x220>
 copy_data+0x129/0x220>
 _prb_read_valid+0x1a0/0x330>
 ? prb_first_seq+0xe0/0xe0>
 ? __might_sleep+0x2f/0xd0>
 ? __zone_watermark_ok+0x180/0x180>
 ? ___might_sleep+0xbe/0xe0>
 prb_read_valid+0x4f/0x60>
 ? _prb_read_valid+0x330/0x330>
 devkmsg_read+0x12e/0x3d0>
 ? __mod_node_page_state+0x1a/0xa0>
 ? info_print_ext_header.constprop.0+0x120/0x120>
 ? __lru_cache_add+0x16c/0x190>
 ? __handle_mm_fault+0x1097/0x1f60>
 vfs_read+0xdc/0x200>
 ksys_read+0xa0/0x130>
 ? kernel_write+0xb0/0xb0>
 ? up_read+0x56/0x130>
 do_syscall_64+0xa0/0x520>
 ? syscall_return_slowpath+0x210/0x210>
 ? do_page_fault+0x399/0x4fa>
 entry_SYSCALL_64_after_hwframe+0x44/0xa9>
RIP: 0033:0x7ff5f39813f2>
Code: c0 e9 c2 fe ff ff 50 48 8d 3d 9a 0d 0a 00 e8 95 ed 01 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24>
RSP: 002b:00007ffc47b3ee58 EFLAGS: 0000024>
c ORIG_RAX: 0000000000000000>
RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007ff5f39813f2>
RDX: 0000000000020000 RSI: 00007ff5f3588000 RDI: 0000000000000003>
RBP: 00007ff5f3588000 R08: 00007ff5f3587010 R09: 0000000000000000>
R10: 0000000000000022 R11: 0000000000000246 R12: 000055f9c8a81c00>
R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000>

	-ss