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From: Miroslav Benes <mbenes@suse.cz>
To: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Kees Cook <keescook@chromium.org>,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	arjan@linux.intel.com, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	kernel-hardening@lists.openwall.com, rick.p.edgecombe@intel.com,
	live-patching@vger.kernel.org, Hongjiu Lu <hongjiu.lu@intel.com>,
	joe.lawrence@redhat.com
Subject: Re: [PATCH v4 00/10] Function Granular KASLR
Date: Fri, 28 Aug 2020 12:21:13 +0200 (CEST)
Message-ID: <alpine.LSU.2.21.2008281216031.29208@pobox.suse.cz> (raw)
In-Reply-To: <46c49dec078cb8625a9c3a3cd1310a4de7ec760b.camel@linux.intel.com>

Leaving Josh's proposals here for reference...

> > I'm not sure how LTO does it, but a few more (half-brained) ideas
> > that
> > could work:
> > 
> > 1) Add a field in kallsyms to keep track of a symbol's original
> > offset
> >    before randomization/re-sorting.  Livepatch could use that field
> > to
> >    determine the original sympos.
> > 
> > 2) In fgkaslr code, go through all the sections and mark the ones
> > which
> >    have duplicates (i.e. same name).  Then when shuffling the
> > sections,
> >    skip a shuffle if it involves a duplicate section.  That way all
> > the
> >    duplicates would retain their original sympos.
> > 
> > 3) Livepatch could uniquely identify symbols by some feature other
> > than
> >    sympos.  For example:
> > 
> >    Symbol/function size - obviously this would only work if
> > duplicately
> >    named symbols have different sizes.
> > 
> >    Checksum - as part of a separate feature we're also looking at
> > giving
> >    each function its own checksum, calculated based on its
> > instruction
> >    opcodes.  Though calculating checksums at runtime could be
> >    complicated by IP-relative addressing.
> > 
> > I'm thinking #1 or #2 wouldn't be too bad.  #3 might be harder.
> > 
> 
> 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?

Thanks
Miroslav


  parent reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200717170008.5949-1-kristen@linux.intel.com>
2020-07-22  9:27 ` Miroslav Benes
2020-07-22 14:39   ` Kees Cook
2020-07-22 14:51     ` Joe Lawrence
2020-07-22 14:56       ` Joe Lawrence
2020-07-22 18:24         ` Kristen Carlson Accardi
2020-07-22 16:07     ` Josh Poimboeuf
2020-07-22 19:42       ` Kees Cook
2020-07-22 19:56         ` Kristen Carlson Accardi
2020-07-22 21:33           ` Josh Poimboeuf
2020-08-21 23:02             ` Kristen Carlson Accardi
2020-08-25 16:16               ` Joe Lawrence
2020-08-28 10:21               ` Miroslav Benes [this message]
2020-08-28 19:24                 ` Josh Poimboeuf
2020-08-03 11:39   ` Evgenii Shatokhin
2020-08-03 17:45     ` Kees Cook
2020-08-03 18:17       ` Joe Lawrence
2020-08-03 19:38         ` Frank Ch. Eigler
2020-08-03 20:11           ` Kees Cook
2020-08-03 21:12             ` Frank Ch. Eigler
2020-08-03 21:41               ` Kees Cook
2020-08-04  0:48                 ` Frank Ch. Eigler
2020-08-04 17:04         ` Jessica Yu
2020-08-04 18:23 ` Joe Lawrence
2020-08-07 16:38   ` Kristen Carlson Accardi
2020-08-07 17:20     ` Kees Cook
2020-08-10 16:10       ` Kristen Carlson Accardi
2020-08-12 17:18   ` Kristen Carlson Accardi

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