kernel-hardening - Re: [RFC 1/6] lib: vsprintf: additional kernel pointer filtering options

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Message-ID: <20170518141203.GB23654@kroah.com>
Date: Thu, 18 May 2017 16:12:03 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Petr Mladek <pmladek@...e.com>
Cc: kernel-hardening@...ts.openwall.com,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	William Roberts <william.c.roberts@...el.com>,
	Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>
Subject: Re: [RFC 1/6] lib: vsprintf: additional kernel pointer filtering
 options

On Tue, May 16, 2017 at 01:58:11PM +0200, Petr Mladek wrote:
> On Fri 2017-05-05 21:06:56, Greg KH wrote:
> > From: Dave Weinstein <olorin@...gle.com>
> > 
> > Add the kptr_restrict setting of 3 which results in both
> > %p and %pK values being replaced by zeros.
> > 
> > Add an additional %pP value inspired by the Grsecurity
> > option which explicitly whitelists pointers for output.
> > 
> > This patch is based on work by William Roberts
> > <william.c.roberts@...el.com>
> > 
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index e3bf4e0f10b5..f4e11dade1ab 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -395,6 +395,16 @@ struct printf_spec {
> >  #define FIELD_WIDTH_MAX ((1 << 23) - 1)
> >  #define PRECISION_MAX ((1 << 15) - 1)
> >  
> > +int kptr_restrict __read_mostly;
> > +
> > +/*
> > + * Always cleanse %p and %pK specifiers
> > + */
> > +static inline int kptr_restrict_always_cleanse_pointers(void)
> 
> The name of the function is very long and still confusing.
> It uses the word "always" but there are many types of pointers
> that are not cleared with this condition, for example %pP, %pa.
> 
> Do we need this helper function at all? It is used
> a weird way, see below.

Thanks for the comments, I'll revise this for the next version, thanks
so much for the review, much appreciated.

thanks,

greg k-h

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