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Date: Thu, 6 Oct 2016 13:23:42 +0000
From: "Roberts, William C" <william.c.roberts@...el.com>
To: Rasmus Villemoes <linux@...musvillemoes.dk>
CC: "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>, "corbet@....net" <corbet@....net>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] printk: introduce kptr_restrict level 3
> -----Original Message-----
> From: Rasmus Villemoes [mailto:linux@...musvillemoes.dk]
> Sent: Wednesday, October 5, 2016 4:53 PM
> To: Roberts, William C <william.c.roberts@...el.com>
> Cc: kernel-hardening@...ts.openwall.com; corbet@....net; linux-
> doc@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] printk: introduce kptr_restrict level 3
>
> On Wed, Oct 05 2016, william.c.roberts@...el.com wrote:
>
> > From: William Roberts <william.c.roberts@...el.com>
> >
> > Some out-of-tree modules do not use %pK and just use %p, as it's the
> > common C paradigm for printing pointers. Because of this,
> > kptr_restrict has no affect on the output and thus, no way to contain
> > the kernel address leak.
> >
> > Introduce kptr_restrict level 3 that causes the kernel to treat %p as
> > if it was %pK and thus always prints zeros.
> >
> > Sample Output:
> > kptr_restrict == 2:
> > p: 00000000604369f4
> > pK: 0000000000000000
> >
> > kptr_restrict == 3:
> > p: 0000000000000000
> > pK: 0000000000000000
> >
> > Signed-off-by: William Roberts <william.c.roberts@...el.com>
> > ---
> > Documentation/sysctl/kernel.txt | 3 ++
> > kernel/sysctl.c | 3 +-
> > lib/vsprintf.c | 107 ++++++++++++++++++++++++----------------
>
> That's a lot of changed lines. Why isn't this just
I moved the nested case into a static local function, I thought it was easier to read than the existing
nested switches. The other reason was so we didn't have kptr_restrict littering that code
and it was contained within the default and K values of the switch.
>
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1719,6 +1719,8 @@ char *pointer(const char *fmt, char *buf, char *end,
> void *ptr,
> case 'G':
> return flags_string(buf, end, ptr, fmt);
> }
> + if (kptr_restrict == 3)
> + ptr = NULL;
> spec.flags |= SMALL;
> if (spec.field_width == -1) {
> spec.field_width = default_width;
>
> ?
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