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Date: Wed, 16 Feb 2022 15:32:41 -0500
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Alexander Lobakin <alexandr.lobakin@...el.com>,
Fāng-ruì Sòng <maskray@...gle.com>,
linux-hardening@...r.kernel.org, x86@...nel.org,
Borislav Petkov <bp@...en8.de>,
Jesse Brandeburg <jesse.brandeburg@...el.com>,
Kristen Carlson Accardi <kristen@...ux.intel.com>,
Kees Cook <keescook@...omium.org>,
Miklos Szeredi <miklos@...redi.hu>,
Ard Biesheuvel <ardb@...nel.org>,
Tony Luck <tony.luck@...el.com>,
Bruce Schlobohm <bruce.schlobohm@...el.com>,
Jessica Yu <jeyu@...nel.org>,
kernel test robot <lkp@...el.com>,
Miroslav Benes <mbenes@...e.cz>,
Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
Jonathan Corbet <corbet@....net>,
Masahiro Yamada <masahiroy@...nel.org>,
Michal Marek <michal.lkml@...kovi.net>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
Christoph Hellwig <hch@....de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Arnd Bergmann <arnd@...db.de>,
Nathan Chancellor <nathan@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Marios Pomonis <pomonis@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
"H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>,
linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
linux-arch@...r.kernel.org, live-patching@...r.kernel.org,
llvm@...ts.linux.dev
Subject: Re: [PATCH v10 02/15] livepatch: avoid position-based search if `-z
unique-symbol` is available
On Mon, Feb 14, 2022 at 10:10:00AM -0800, Josh Poimboeuf wrote:
> On Mon, Feb 14, 2022 at 01:24:33PM +0100, Alexander Lobakin wrote:
> > > One idea I mentioned before, it may be worth exploring changing the "F"
> > > in FGKASLR to "File" instead of "Function". In other words, only
> > > shuffle at an object-file granularity. Then, even with duplicates, the
> > > <file+function> symbol pair doesn't change in the symbol table. And as
> > > a bonus, it should help FGKASLR i-cache performance, significantly.
> >
> > Yeah, I keep that in mind. However, this wouldn't solve the
> > duplicate static function names problem, right?
> > Let's say you have a static function f() in file1 and f() in file2,
> > then the layout each boot can be
> >
> > .text.file1 or .text.file2
> > f() f()
> > .text.file2 .text.file1
> > f() f()
> >
> > and position-based search won't work anyway, right?
>
> Right, so we'd have to abandon position-based search in favor of
> file+func based search.
>
> It's not perfect because there are still a few file+func duplicates.
> But it might be good enough. We would presumably just refuse to patch a
> duplicate. Or we could remove them (and enforce their continued removal
> with tooling-based warnings).
>
You're talking about duplicate file+func combinations as stored in the
symbol table?
>From a recent rhel-9 development kernel:
$ readelf --wide --symbols vmlinux | \
awk '$4=="FILE" { f=$NF } $4=="OBJECT" || $4=="FUNC" { print $4 " " f "::" $NF }' | \
sort | uniq -c | sort -n | awk '$1 != 1'
2 FUNC bus.c::new_id_store
2 FUNC core.c::native_read_msr
2 FUNC core.c::type_show
2 FUNC diag.c::sk_diag_fill.constprop.0
2 FUNC hid-core.c::hid_exit
2 FUNC hid-core.c::hid_init
2 FUNC inode.c::remove_one
2 FUNC iommu.c::__list_del_entry
2 FUNC msr.c::msr_init
2 FUNC msr.c::msr_read
2 FUNC proc.c::c_next
2 FUNC proc.c::c_start
2 FUNC proc.c::c_stop
2 FUNC raw.c::copy_overflow
2 FUNC raw.c::dst_output
2 FUNC route.c::dst_discard
2 FUNC sysfs.c::name_show
2 FUNC udp.c::copy_overflow
2 FUNC udp.c::udp_lib_close
2 FUNC udp.c::udp_lib_hash
2 FUNC udp.c::udplite_getfrag
2 FUNC udplite.c::udp_lib_close
2 FUNC udplite.c::udp_lib_hash
2 FUNC udplite.c::udplite_sk_init
2 OBJECT acpi.c::__func__.0
2 OBJECT amd.c::__already_done.10
2 OBJECT amd.c::__func__.4
2 OBJECT amd.c::__func__.5
2 OBJECT bus.c::driver_attr_new_id
2 OBJECT bus.c::__func__.1
2 OBJECT bus.c::__func__.2
2 OBJECT bus.c::__func__.3
2 OBJECT bus.c::__func__.4
2 OBJECT bus.c::__func__.5
2 OBJECT bus.c::__func__.6
2 OBJECT bus.c::__func__.7
2 OBJECT bus.c::__func__.8
2 OBJECT bus.c::__func__.9
2 OBJECT cgroup.c::__func__.0
2 OBJECT class.c::__func__.0
2 OBJECT class.c::__func__.1
2 OBJECT class.c::__func__.3
2 OBJECT class.c::__func__.5
2 OBJECT class.c::__key.0
2 OBJECT class.c::__key.1
2 OBJECT class.c::__key.4
2 OBJECT core.c::__already_done.18
2 OBJECT core.c::__already_done.19
2 OBJECT core.c::__already_done.3
2 OBJECT core.c::dev_attr_size
2 OBJECT core.c::dev_attr_start
2 OBJECT core.c::dev_attr_type
2 OBJECT core.c::empty_attrs
2 OBJECT core.c::__func__.10
2 OBJECT core.c::__func__.14
2 OBJECT core.c::__func__.7
2 OBJECT core.c::__func__.9
2 OBJECT core.c::__key.0
2 OBJECT core.c::__key.2
2 OBJECT core.c::__key.3
2 OBJECT dev.c::__func__.0
2 OBJECT dir.c::__func__.3
2 OBJECT driver.c::__func__.0
2 OBJECT fib_rules.c::__msg.0
2 OBJECT file.c::__func__.2
2 OBJECT file.c::__key.1
2 OBJECT file.c::__key.2
2 OBJECT hpet.c::__func__.4
2 OBJECT icmp.c::__func__.1
2 OBJECT inode.c::__func__.1
2 OBJECT inode.c::__func__.3
2 OBJECT intel.c::__already_done.10
2 OBJECT intel.c::__already_done.11
2 OBJECT intel.c::__already_done.13
2 OBJECT ioctl.c::__func__.0
2 OBJECT iommu.c::__already_done.15
2 OBJECT iommu.c::__func__.10
2 OBJECT iommu.c::__func__.2
2 OBJECT iommu.c::_rs.13
2 OBJECT iommu.c::_rs.5
2 OBJECT iommu.c::_rs.9
2 OBJECT irq.c::__func__.0
2 OBJECT irq.c::__func__.2
2 OBJECT irqdomain.c::__func__.0
2 OBJECT irqdomain.c::__func__.1
2 OBJECT irqdomain.c::__func__.3
2 OBJECT main.c::__func__.10
2 OBJECT main.c::__func__.11
2 OBJECT main.c::__func__.3
2 OBJECT main.c::__func__.4
2 OBJECT main.c::__func__.5
2 OBJECT manage.c::__func__.1
2 OBJECT mount.c::__func__.0
2 OBJECT msr.c::__func__.0
2 OBJECT ping.c::__func__.1
2 OBJECT property.c::__func__.3
2 OBJECT qos.c::__func__.0
2 OBJECT qos.c::__func__.2
2 OBJECT resource.c::__func__.1
2 OBJECT route.c::__key.0
2 OBJECT route.c::__msg.1
2 OBJECT route.c::__msg.2
2 OBJECT route.c::__msg.3
2 OBJECT route.c::__msg.4
2 OBJECT route.c::__msg.5
2 OBJECT route.c::__msg.6
2 OBJECT swap.c::__func__.0
2 OBJECT syncookies.c::___done.1
2 OBJECT syncookies.c::msstab
2 OBJECT syncookies.c::___once_key.2
2 OBJECT sysfs.c::dev_attr_name
2 OBJECT sysfs.c::__key.1
2 OBJECT sysfs.c::power_attrs
2 OBJECT udp.c::descriptor.12
2 OBJECT udp.c::descriptor.13
2 OBJECT udp.c::__func__.2
2 OBJECT udp.c::__func__.3
2 OBJECT udp.c::__func__.4
2 OBJECT utils.c::__func__.5
3 FUNC core.c::cmask_show
3 FUNC core.c::edge_show
3 FUNC core.c::event_show
3 FUNC core.c::inv_show
3 FUNC core.c::umask_show
3 FUNC inode.c::init_once
3 OBJECT acpi.c::__func__.1
3 OBJECT core.c::format_attr_cmask
3 OBJECT core.c::format_attr_edge
3 OBJECT core.c::format_attr_event
3 OBJECT core.c::format_attr_inv
3 OBJECT core.c::format_attr_umask
3 OBJECT core.c::__func__.6
3 OBJECT core.c::__func__.8
3 OBJECT file.c::__key.3
3 OBJECT generic.c::__func__.0
3 OBJECT iommu.c::__func__.0
3 OBJECT iommu.c::__func__.1
3 OBJECT iommu.c::__func__.8
3 OBJECT main.c::__func__.0
3 OBJECT main.c::__func__.1
3 OBJECT main.c::__func__.6
3 OBJECT quirks.c::__func__.0
3 OBJECT sysfs.c::__func__.0
4 OBJECT core.c::__func__.4
5 OBJECT inode.c::tokens
6 OBJECT core.c::__func__.3
6 OBJECT core.c::__func__.5
7 OBJECT core.c::__func__.1
8 OBJECT core.c::__func__.0
8 OBJECT core.c::__func__.2
We could probably minimize the FUNC duplicates with unique names, but
I'm not as optimistic about the OBJECTs as most are created via macros
like __already_done.X. Unless clever macro magic?
Next question: what are the odds that these entries, at least the ones
we can't easily rename, need disambiguity for livepatching? or
kpatch-build for related purposes?
-- Joe
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