linux-kernel - Re: [PATCH] arm64: mm: Don't use %pK through printk

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Message-ID: <20250318161109.GA13981@willie-the-truck>
Date: Tue, 18 Mar 2025 16:11:11 +0000
From: Will Deacon <will@...nel.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: mm: Don't use %pK through printk

On Mon, Feb 24, 2025 at 03:12:54PM +0100, Thomas Weißschuh wrote:
> On Fri, Feb 21, 2025 at 02:55:14PM +0000, Will Deacon wrote:
> > On Mon, Feb 17, 2025 at 08:39:06AM +0100, Thomas Weißschuh wrote:
> > > Restricted pointers ("%pK") are not meant to be used through printk().
> > > It can unintentionally expose security sensitive, raw pointer values.
> > > 
> > > Use regular pointer formatting instead.
> > > 
> > > Link: https://lore.kernel.org/lkml/20250113171731-dc10e3c1-da64-4af0-b767-7c7070468023@linutronix.de/
> > > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> > > ---
> > >  arch/arm64/mm/physaddr.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
> > > index cde44c13dda1bc0924d2d50369ad87f544a0a802..7d94e09b01b35094e883875a46b979666549095c 100644
> > > --- a/arch/arm64/mm/physaddr.c
> > > +++ b/arch/arm64/mm/physaddr.c
> > > @@ -10,7 +10,7 @@
> > >  phys_addr_t __virt_to_phys(unsigned long x)
> > >  {
> > >  	WARN(!__is_lm_address(__tag_reset(x)),
> > > -	     "virt_to_phys used for non-linear address: %pK (%pS)\n",
> > > +	     "virt_to_phys used for non-linear address: %p (%pS)\n",
> > >  	      (void *)x,
> > >  	      (void *)x);
> > 
> > This is part of a WARN() and knowing the actual address may well be
> > useful in debugging. I suspect it also ends up being dumped as part of
> > the register dump _anyway_.
> 
> That makes sense, especially the value being part of the register dump.
> OTOH in the default kernel configuration (kptr_restrict==0), %pK is an alias to
> %p and also hashing the pointers. And so far nobody seems to have cared.
> 
> If you prefer I can also change it to %px, to specifically show the value.
> My main goal is to remove %pK, as it's prone to misuse.

Probably best to ignore me, then, and keep the existing behaviour with
your change (as your patch is doing).

Thanks,

Will