[v2,0/4] Implement indirect external access marker

  Changes in the v2 patch.

1. Rename GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION to
GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS.
2. Rename the option to -z [no]indirect-extern-access and move it to
ld/emulparams/extern_protected_data.sh.
3. Clear the indirect external access bit in executable when there are
non-GOT or non-PLT relocations in relocatable input files without this
bit set.

---
On systems with copy relocation:
* A copy in executable is created for the definition in a shared library
at run-time by ld.so.
* The copy is referenced by executable and shared libraries.
* Executable can access the copy directly.

Issues are:
* Overhead of a copy, time and space, may be visible at run-time.
* Read-only data in the shared library becomes read-write copy in
executable at run-time.
* Local access to data with the STV_PROTECTED visibility in the shared
library must use GOT.

On systems without function descriptor, function pointers vary depending
on where and how the functions are defined.
* If the function is defined in executable, it can be the address of
function body.
* If the function, including the function with STV_PROTECTED visibility,
is defined in the shared library, it can be the address of the PLT entry
in executable or shared library.

Issues are:
* The address of function body may not be used as its function pointer.
* ld.so needs to search loaded shared libraries for the function pointer
of the function with STV_PROTECTED visibility.

Here is a proposal to remove copy relocation and use canonical function
pointer:

1. Accesses, including in PIE and non-PIE, to undefined symbols must
use GOT.
  a. Linker may optimize out GOT access if the data is defined in PIE or
  non-PIE.
2. Read-only data in the shared library remain read-only at run-time
3. Address of global data with the STV_PROTECTED visibility in the shared
library is the address of data body.
  a. Can use IP-relative access.
  b. May need GOT without IP-relative access.
4. For systems without function descriptor,
  a. All global function pointers of undefined functions in PIE and
  non-PIE must use GOT.  Linker may optimize out GOT access if the
  function is defined in PIE or non-PIE.
  b. Function pointer of functions with the STV_PROTECTED visibility in
  executable and shared library is the address of function body.
   i. Can use IP-relative access.
   ii. May need GOT without IP-relative access.
   iii. Branches to undefined functions may use PLT.
5. Single global definition marker:

Add GNU_PROPERTY_1_NEEDED:

#define GNU_PROPERTY_1_NEEDED GNU_PROPERTY_UINT32_OR_LO

to indicate the needed properties by the object file.

Add GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS:

#define GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS (1U << 0)

to indicate that the object file requires canonical function pointers and
cannot be used with copy relocation.  This bit should be cleared in
executable when there are non-GOT or non-PLT relocations in relocatable
input files without this bit set.

  a. Protected symbol access within the shared library can be treated as
  local.
  b. Copy relocation should be disallowed at link-time and run-time.
  c. GOT function pointer reference is required at link-time and run-time.

The indirect external access marker can be used in the following ways:

1. Linker can decide the best way to resolve a relocation against a
protected symbol before seeing all relocations against the symbol.
2. Dynamic linker can decide if it is an error to have a copy relocation
in executable against the protected symbol in a shared library by checking
if the shared library is built with -fno-direct-extern-access.

Dynamic linker changes:

* Scan the indirect external access marker on all components, including
the executable and its dependency shared libraries.
* When performing symbol lookup for references in executable without
indirect external access:

  1. Disallow copy relocations in executable against protected data
     symbols in a shared object with indirect external access.
  2. Disallow non-zero symbol values of undefined function symbols in
     executable, which are used as the function pointer, against protected
     function symbols in a shared object with indirect external access.

The corresponding binutils patches are posted at

https://sourceware.org/pipermail/binutils/2021-June/117153.html

and GCC patches are posted at

https://gcc.gnu.org/pipermail/gcc-patches/2021-June/573633.html

We can replace hidden function symbols with protected symbols and build
glibc with -fno-direct-extern-access.

H.J. Lu (4):
  Initial support for GNU_PROPERTY_1_NEEDED
  Check -z indirect-extern-access and -fno-direct-extern-access
  Add run-time chesk for indirect external access
  Update tests for protected data and function symbols

 configure                      |  59 +++++++++++++++
 configure.ac                   |  37 ++++++++++
 elf/Makefile                   |  54 ++++++++++++++
 elf/dl-lookup.c                |   5 ++
 elf/elf.h                      |  17 +++++
 elf/tst-protected1moda.c       |  10 +--
 elf/tst-protected1modb.c       |   4 +-
 elf/tst-protected2a.c          | 130 +++++++++++++++++++++++++++++++++
 elf/tst-protected2apie.c       |   1 +
 elf/tst-protected2b.c          | 121 ++++++++++++++++++++++++++++++
 elf/tst-protected2bpie.c       |   1 +
 elf/tst-protected2mod.h        |  35 +++++++++
 elf/tst-protected2moda.c       |  52 +++++++++++++
 elf/tst-protected2moda2.c      |  41 +++++++++++
 elf/tst-protected2modb.c       |  45 ++++++++++++
 elf/tst-protected2modb2.c      |  28 +++++++
 sysdeps/generic/dl-prop.h      |   9 ++-
 sysdeps/generic/dl-protected.h |  54 ++++++++++++++
 sysdeps/generic/link_map.h     |   3 +-
 sysdeps/x86/dl-prop.h          |  19 +++--
 sysdeps/x86/link_map.h         |   2 +
 21 files changed, 710 insertions(+), 17 deletions(-)
 create mode 100644 elf/tst-protected2a.c
 create mode 100644 elf/tst-protected2apie.c
 create mode 100644 elf/tst-protected2b.c
 create mode 100644 elf/tst-protected2bpie.c
 create mode 100644 elf/tst-protected2mod.h
 create mode 100644 elf/tst-protected2moda.c
 create mode 100644 elf/tst-protected2moda2.c
 create mode 100644 elf/tst-protected2modb.c
 create mode 100644 elf/tst-protected2modb2.c
 create mode 100644 sysdeps/generic/dl-protected.h