Re: [PATCH v3] module: Fix display of wrong module .text address

[Jessica Yu]

+++ Thomas Richter [18/04/18 09:14 +0200]:
> 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>

Thanks for turning this into a real patch. Looks good to me, if Linus
wants to take it directly:

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Otherwise I can take this up my tree.

As Linus mentioned, we should technically be checking the opening
task's credentials/capabilities, but converting everything to pass the
actual struct seq_file/file to the sysfs show handlers would be fairly
painful :/ At least those /sys/module/*/sections/ files are all set to
0400. I think this fix is sufficient for now.

> ---
> 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);
> }
>
> static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
> --
> 2.14.3