linux-kernel - Re: [RFC PATCH 08/11] x86: Add support for finer grained KASLR

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Message-ID: <9f337efdf226e51e3f5699243623e5de7505ac94.camel@linux.intel.com>
Date:   Thu, 06 Feb 2020 09:25:01 -0800
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        arjan@...ux.intel.com, rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH 08/11] x86: Add support for finer grained KASLR

On Thu, 2020-02-06 at 15:52 +0100, Peter Zijlstra wrote:
> On Thu, Feb 06, 2020 at 04:06:17AM -0800, Kees Cook wrote:
> > On Thu, Feb 06, 2020 at 11:38:30AM +0100, Peter Zijlstra wrote:
> > > On Wed, Feb 05, 2020 at 02:39:47PM -0800, Kristen Carlson Accardi
> > > wrote:
> > > > +static long __start___ex_table_addr;
> > > > +static long __stop___ex_table_addr;
> > > > +static long _stext;
> > > > +static long _etext;
> > > > +static long _sinittext;
> > > > +static long _einittext;
> > > 
> > > Should you not also adjust __jump_table, __mcount_loc,
> > > __kprobe_blacklist and possibly others that include text
> > > addresses?
> > 
> > These don't appear to be sorted at build time. 
> 
> The ORC tables are though:
> 
>   57fa18994285 ("scripts/sorttable: Implement build-time ORC unwind
> table sorting")
> 
> > AIUI, the problem with
> > ex_table and kallsyms is that they're preprocessed at build time
> > and
> > opaque to the linker's relocation generation.
> 
> I was under the impression these tables no longer had relocation
> data;
> that since they're part of the main kernel, the final link stage
> could
> completely resolve them.
> 
> That said, I now see we actually have .rela__extable
> .rela.orc_unwind_ip
> etc.

That's right - all of these tables that you mention had relocs and thus
I did not have to do anything special for them. The orc_unwind_ip
tables get sorted during unwind_init(). If they are needed earlier than
that, then they could be re-sorted like we do with the exception table.