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

[David Hildenbrand]

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@localhost ~]# cat /proc/kallsyms | grep ksys_read
ffffffff8927a800 T ksys_readahead
ffffffff89333660 T ksys_read

[root@localhost ~]# 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