linux-kernel - Re: [BUG] general protection fault when reading /proc/kcore

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Date:   Mon, 16 Aug 2021 19:49:15 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Jiri Olsa <jolsa@...hat.com>, Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [BUG] general protection fault when reading /proc/kcore

On 16.08.21 19:34, Jiri Olsa wrote:
> hi,
> I'm getting fault below when running:
> 
> 	# cat /proc/kallsyms | grep ksys_read
> 	ffffffff8136d580 T ksys_read
> 	# objdump -d --start-address=0xffffffff8136d580 --stop-address=0xffffffff8136d590 /proc/kcore
> 
> 	/proc/kcore:     file format elf64-x86-64
> 
> 	Segmentation fault
> 
> any idea? config is attached

Just tried with a different config on 5.14.0-rc6+

[root@...alhost ~]# cat /proc/kallsyms | grep ksys_read
ffffffff8927a800 T ksys_readahead
ffffffff89333660 T ksys_read

[root@...alhost ~]# objdump -d --start-address=0xffffffff89333660 
--stop-address=0xffffffff89333670

a.out:     file format elf64-x86-64



The kern_addr_valid(start) seems to fault in your case, which is weird, 
because it merely walks the page tables. But it seems to complain about 
a non-canonical address 0xf887ffcbff000

Can you post your QEMU cmdline? Did you test this on other kernel versions?

Thanks!

-- 
Thanks,

David / dhildenb