On Mon, May 06, 2019 at 03:47:05PM +0200, Simon Horman wrote:
> On Sat, May 04, 2019 at 02:42:53AM +0200, Eugeniu Rosca wrote:
> > Starting with v4.15-rc2 commit ad67b74d2469d9 ("printk: hash addresses
> > printed with %p"), enabling debug prints in sh-sci.c would generate
> > output like below confusing the users who try to sneak into the
> > internals of the driver:
> >
> > sh-sci e6e88000.serial: sci_request_dma: TX: got channel (____ptrval____)
> > sh-sci e6e88000.serial: sci_request_dma: mapped 4096@(____ptrval____) to 0x00000006798bf000
> > sh-sci e6e88000.serial: sci_request_dma: RX: got channel (____ptrval____)
> > sh-sci e6e88000.serial: sci_dma_tx_work_fn: (____ptrval____): 0...2, cookie 2
> >
> > There are two possible fixes for that:
> > - get rid of '%p' prints if they don't reveal any useful information
> > - s/%p/%px/, since it is unlikely we have any concerns leaking the
> > pointer values when running a debug/non-production kernel
>
> I am concerned that this may expose information in circumstances
> where it is undesirable. Is it generally accepted practice to
> use %px in conjunction with dev_dbg() ?
>
> ...
Below commits performed a similar s/%p/%px/ update in debug context:
Authors (CC-ed) Commit Subject
----------------------------------------
Christophe Leroy b18f0ae92b0a1d ("powerpc/prom: fix early DEBUG messages")
Helge Deller 3847dab7742186 ("parisc: Add alternative coding infrastructure")
Michael Neuling 51c3c62b58b357 ("powerpc: Avoid code patching freed init sections")
Kuninori Morimoto dabdbe3ae0cb9a ("ASoC: rsnd: don't use %p for dev_dbg()")
Philip Yang fa7e65147e5dca ("drm/amdkfd: use %px to print user space address instead of %p")
Matthew Wilcox 68c1f08203f2b0 ("lib/list_debug.c: print unmangled addresses")
Borislav Petkov 0e6c16c652cada ("x86/alternative: Print unadorned pointers")
Darrick J. Wong c96900435fa9fd ("xfs: use %px for data pointers when debugging")
Helge Deller 04903c06b4854d ("parisc: Show unhashed HPA of Dino chip")
To quote Matthew, with respect to any debug prints:
If an attacker can force this message to be printed, we've already lost.
In any case, I won't be affected much if the change is not accepted,
since it doesn't resolve any major issue on my end. Thanks!
--
Best Regards,
Eugeniu.
