linux-kernel - Re: [PATCH v4 00/10] Function Granular KASLR

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Date:   Fri, 28 Aug 2020 14:24:13 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, arjan@...ux.intel.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, rick.p.edgecombe@...el.com,
        live-patching@...r.kernel.org, Hongjiu Lu <hongjiu.lu@...el.com>,
        joe.lawrence@...hat.com
Subject: Re: [PATCH v4 00/10] Function Granular KASLR

On Fri, Aug 28, 2020 at 12:21:13PM +0200, Miroslav Benes wrote:
> > Hi there! I was trying to find a super easy way to address this, so I
> > thought the best thing would be if there were a compiler or linker
> > switch to just eliminate any duplicate symbols at compile time for
> > vmlinux. I filed this question on the binutils bugzilla looking to see
> > if there were existing flags that might do this, but H.J. Lu went ahead
> > and created a new one "-z unique", that seems to do what we would need
> > it to do. 
> > 
> > https://sourceware.org/bugzilla/show_bug.cgi?id=26391
> > 
> > When I use this option, it renames any duplicate symbols with an
> > extension - for example duplicatefunc.1 or duplicatefunc.2. You could
> > either match on the full unique name of the specific binary you are
> > trying to patch, or you match the base name and use the extension to
> > determine original position. Do you think this solution would work?
> 
> Yes, I think so (thanks, Joe, for testing!).
> 
> It looks cleaner to me than the options above, but it may just be a matter 
> of taste. Anyway, I'd go with full name matching, because -z unique-symbol 
> would allow us to remove sympos altogether, which is appealing.
> 
> > If
> > so, I can modify livepatch to refuse to patch on duplicated symbols if
> > CONFIG_FG_KASLR and when this option is merged into the tool chain I
> > can add it to KBUILD_LDFLAGS when CONFIG_FG_KASLR and livepatching
> > should work in all cases. 
> 
> Ok.
> 
> Josh, Petr, would this work for you too?

Sounds good to me.  Kristen, thanks for finding a solution!

-- 
Josh