[PATCH] drm: Print unadorned pointers

[Maarten Lankhorst]

Op 18-04-18 om 11:59 schreef Alexey Brodkin:
> On Wed, 2018-04-18 at 11:29 +0200, Maarten Lankhorst wrote:
>> Op 18-04-18 om 11:24 schreef Alexey Brodkin:
>>> After commit ad67b74 ("printk: hash addresses printed with %p")
>>> pointers are being hashed when printed. However, this makes
>>> debug output completely useless. Switch to %px in order to see the
>>> unadorned kernel pointers.
>>>
>>> This was done with the following one-liner:
>>>  find drivers/gpu/drm -type f -name "*.c" -exec sed -r -i '/DRM_DEBUG|KERN_DEBUG|pr_debug/ s/%p\b/%px/g' {} +
>> So first we plug a kernel information leak hole, then we introduce it again? Seems like a terrible idea..
> Well security concerns are good but what about us poor kernel developers?
> Those debug prints are supposed to help us to deal with stuff we develop or fix.
>
> Frankly I was quite surprised when first saw what was "unique hashed ID" instead
> of real pointer value. And what's worse there's no way to get previous behavior back.
> So now we have to manually patch sources here and there to get meaningful data, right?
>
> I wouldn't bother sending this patch if there was Kconfig option reverting %p behavior
> but that was never implemented.
>
> -Alexey

There's %pK for kernel pointers. It does what you want and can be toggled with kptr_restrict, without introducing security holes. :)

Perhaps split up this patch per driver, and handle the other variations as well?

DRM_NOTE DRM_WARN DRM_INFO DRM_ERROR.


~Maarten