On 05/02/2018 04:20 AM, Kees Cook wrote:
> On Wed, Apr 18, 2018 at 12:14 AM, Thomas Richter <tmricht@xxxxxxxxxxxxx> wrote:
>> Reading file /proc/modules shows the correct address:
>> [root@s35lp76 ~]# cat /proc/modules | egrep '^qeth_l2'
>> qeth_l2 94208 1 - Live 0x000003ff80401000
>>
>> and reading file /sys/module/qeth_l2/sections/.text
>> [root@s35lp76 ~]# cat /sys/module/qeth_l2/sections/.text
>> 0x0000000018ea8363
>> displays a random address.
>>
>> This breaks the perf tool which uses this address on s390
>> to calculate start of .text section in memory.
>>
>> Fix this by printing the correct (unhashed) address.
>>
>> Thanks to Jessica Yu for helping on this.
>>
>> Fixes: ef0010a30935 ("vsprintf: don't use 'restricted_pointer()' when not restricting")
>> Cc: <stable@xxxxxxxxxxxxxxx> # v4.15+
>> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
>> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
>> ---
>> kernel/module.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/module.c b/kernel/module.c
>> index a6e43a5806a1..40b42000bd80 100644
>> --- a/kernel/module.c
>> +++ b/kernel/module.c
>> @@ -1472,7 +1472,8 @@ static ssize_t module_sect_show(struct module_attribute *mattr,
>> {
>> struct module_sect_attr *sattr =
>> container_of(mattr, struct module_sect_attr, mattr);
>> - return sprintf(buf, "0x%pK\n", (void *)sattr->address);
>> + return sprintf(buf, "0x%px\n", kptr_restrict < 2 ?
>> + (void *)sattr->address : NULL);
>
> Errr... this looks reversed to me.
>
> I would expect: "kptr_restrict < 2 ? NULL : (void *)sattr->address"
>
> -Kees
>
I am confused:
In my patch, if kptr_restrict == 2 it prints NULL, which kptr_restrict
being 0 or 1 it prints the address.
In your comment if kptr_restrict == 2 it prints the address, which
kptr_restrict being 0 or 1 it prints NULL.
Looking into Documentation/sysctl/kernel.txt:
When kptr_restrict is set to (2), kernel pointers printed using
%pK will be replaced with 0's regardless of privileges.
With my patch, setting kptr_restrict to 0 or 1
prints the real kernel address (format %px, unmodified address
according to Documentation/printk-formats.txt).
I have tested this on s390 (which is the only arch using file
/sys/module/<XXX>/sections/.text) in the perf tool.
root@s8360047 ~]# sysctl kernel.kptr_restrict
kernel.kptr_restrict = 0
[root@s8360047 ~]# cat /proc/modules | egrep '^qeth_l2'
qeth_l2 102400 1 - Live 0x000003ff8034d000
[root@s8360047 ~]# cat /sys/module/qeth_l2/sections/.text
0x000003ff8034da68
[root@s8360047 ~]# sysctl -w kernel.kptr_restrict=2
kernel.kptr_restrict = 2
[root@s8360047 ~]# cat /proc/modules | egrep '^qeth_l2'
qeth_l2 102400 1 - Live 0x0000000000000000
[root@s8360047 ~]# cat /sys/module/qeth_l2/sections/.text
0x0000000000000000
[root@s8360047 ~]# uname -a
Linux s8360047 4.17.0-rc3m-perf+ #6 SMP PREEMPT Wed May 2 10:02:38 CEST 2018 s390x s390x s390x GNU/Linux
[root@s8360047 ~]#
Hope this helps.
--
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
