+++ Christian Borntraeger [16/04/18 12:53 +0200]:
Can this be related to
commit ef0010a30935de4e0211cbc7bdffc30446cdee9b
   vsprintf: don't use 'restricted_pointer()' when not restricting
and related commits?

To me it looks like %pk is always printing the hash, but never the real pointer 
no matter what kernel.kptr_restrict says.

(Added Kees and Tobin to CC)

Can confirm, a git bisect confirms that ef0010a3093 was the first bad commit.

And yeah, the default seems to be to always hash the pointer address now,
regardless of kptr_restrict. See Documentation/sysctl/kernel.txt:

   When kptr_restrict is set to 0 (the default) the address is hashed before
   printing. (This is the equivalent to %p.)

And to quote from the relevant patchset (https://lkml.org/lkml/2017/11/28/1593):

  The added advantage of hashing %p is that security is now opt-out, if
  you _really_ want the address you have to work a little harder and use %px.

So for users of /sys/module/*/sections, we will need to work around
this and possibly use %px for the real address. But perhaps we should
base the usage of %px on kptr_restrict? That is what m_show() in
module.c currently does, which is why you get the correct address when
you look at /proc/modules (it uses %px and either shows 0's or the
real address based on kallsyms_show_value()). module_sect_show() uses
%pK so it's getting hashed. Is there a better way of doing this?


On 04/16/2018 08:23 AM, Christian Borntraeger wrote:
FWIW, this breaks at least perf capability to resolve module symbols.
Adding some more CCs for perf and module.

On 04/16/2018 07:51 AM, Thomas-Mich Richter wrote:
I just installed 4.16.0 and discovered the module .text address is
wrong. It happens on s390 and x86 platforms. I have not tested others.

Here is the issue, I have used module qeth_l2 on s390 which is the
ethernet device driver:

root@s35lp76 ~]# lsmod
Module                  Size  Used by
qeth_l2                94208  1

[root@s35lp76 ~]# cat /proc/modules | egrep '^qeth_l2'
qeth_l2 94208 1 - Live 0x000003ff80401000   <---- This is the correct address 
in memory
[root@s35lp76 ~]# cat /sys/module/qeth_l2/sections/.text
0x0000000018ea8363      <---- This is the wrong address
[root@s35lp76 ~]#

File /sys/module/qeth_l2/sections/.text displays a very strange
address which is definitely wrong. It should be something like

Same on x86.

I have checked file kernel/module.c function add_sect_attrs()
and it calls module_sect_show() when the sysfs file is read.
And module_sect_show() uses

  sprintf(buf, "0x%pK\n", (void *)sattr->address);

and my sysctl setting should be correct:
[root@s35lp76 linux]# sysctl -a | fgrep kernel.kptr_restrict
kernel.kptr_restrict = 0
[root@s35lp76 linux]#

I wonder if somebody else has seen this issue?
Ideas how to fix this?


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