Re: [PATCH v10 02/15] livepatch: avoid position-based search if `-z unique-symbol` is available

[Joe Lawrence]

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