Intel Control-flow Enforcement Technology (CET) instructions:
https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-en
forcement-technology-preview.pdf
includes Indirect Branch Tracking (IBT) and Shadow Stack (SHSTK).
GNU_PROPERTY_X86_FEATURE_1_IBT is added to GNU program property to
indicate that all executable sections are compatible with IBT when
ENDBR instruction starts each valid target where an indirect branch
instruction can land. Linker sets GNU_PROPERTY_X86_FEATURE_1_IBT on
output only if it is set on all relocatable inputs.
On an IBT capable processor, the following steps should be taken:
1. When loading an executable without an interpreter, enable IBT and
lock IBT if GNU_PROPERTY_X86_FEATURE_1_IBT is set on the executable.
2. When loading an executable with an interpreter, enable IBT if
GNU_PROPERTY_X86_FEATURE_1_IBT is set on the interpreter.
a. If GNU_PROPERTY_X86_FEATURE_1_IBT isn't set on the executable,
disable IBT.
b. Lock IBT.
3. If IBT is enabled, when loading a shared object without
GNU_PROPERTY_X86_FEATURE_1_IBT:
a. If legacy interwork is allowed, then mark all pages in executable
PT_LOAD segments in legacy code page bitmap. Failure of legacy code
page bitmap allocation causes an error.
b. If legacy interwork isn't allowed, it causes an error.
GNU_PROPERTY_X86_FEATURE_1_SHSTK is added to GNU program property to
indicate that all executable sections are compatible with SHSTK where
return address popped from shadow stack always matches return address
popped from normal stack. Linker sets GNU_PROPERTY_X86_FEATURE_1_SHSTK
on output only if it is set on all relocatable inputs.
On a SHSTK capable processor, the following steps should be taken:
1. When loading an executable without an interpreter, enable SHSTK if
GNU_PROPERTY_X86_FEATURE_1_SHSTK is set on the executable.
2. When loading an executable with an interpreter, enable SHSTK if
GNU_PROPERTY_X86_FEATURE_1_SHSTK is set on interpreter.
a. If GNU_PROPERTY_X86_FEATURE_1_SHSTK isn't set on the executable
or any shared objects loaded via the DT_NEEDED tag, disable SHSTK.
b. Otherwise lock SHSTK.
3. After SHSTK is enabled, it is an error to load a shared object
without GNU_PROPERTY_X86_FEATURE_1_SHSTK.
To enable CET support in glibc, --enable-cet is required to configure
glibc. When CET is enabled, both compiler and assembler must support
CET. Otherwise, it is a configure-time error.
To support CET run-time control,
1. _dl_x86_feature_1 is added to the writable ld.so namespace to indicate
if IBT or SHSTK are enabled at run-time. It should be initialized by
init_cpu_features.
2. For dynamic executables:
a. A l_cet field is added to struct link_map to indicate if IBT or
SHSTK is enabled in an ELF module. _dl_process_pt_note or
_rtld_process_pt_note is called to process PT_NOTE segment for
GNU program property and set l_cet.
b. _dl_open_check is added to check IBT and SHSTK compatibilty when
dlopening a shared object.
3. Replace i386 _dl_runtime_resolve and _dl_runtime_profile with
_dl_runtime_resolve_shstk and _dl_runtime_profile_shstk, respectively if
SHSTK is enabled.
CET run-time control can be changed via GLIBC_TUNABLES with
$ export GLIBC_TUNABLES=glibc.tune.x86_shstk=[permissive|on|off]
$ export GLIBC_TUNABLES=glibc.tune.x86_ibt=[permissive|on|off]
1. permissive: SHSTK is disabled when dlopening a legacy ELF module.
2. on: IBT or SHSTK are always enabled, regardless if there are IBT or
SHSTK bits in GNU program property.
3. off: IBT or SHSTK are always disabled, regardless if there are IBT or
SHSTK bits in GNU program property.
<cet.h> from CET-enabled GCC is automatically included by assembly codes
to add GNU_PROPERTY_X86_FEATURE_1_IBT and GNU_PROPERTY_X86_FEATURE_1_SHSTK
to GNU program property. _CET_ENDBR is added at the entrance of all
assembly functions whose address may be taken. _CET_NOTRACK is used to
insert NOTRACK prefix with indirect jump table to support IBT. It is
defined as notrack when _CET_NOTRACK is defined in <cet.h>.
[BZ #21598]
* configure.ac: Add --enable-cet.
* configure: Regenerated.
* elf/Makefille (all-built-dso): Add a comment.
* elf/dl-load.c (filebuf): Moved before "dynamic-link.h".
Include <dl-prop.h>.
(_dl_map_object_from_fd): Call _dl_process_pt_note on PT_NOTE
segment.
* elf/dl-open.c: Include <dl-prop.h>.
(dl_open_worker): Call _dl_open_check.
* elf/rtld.c: Include <dl-prop.h>.
(dl_main): Call _rtld_process_pt_note on PT_NOTE segment. Call
_rtld_main_check.
* sysdeps/generic/dl-prop.h: New file.
* sysdeps/i386/dl-cet.c: Likewise.
* sysdeps/unix/sysv/linux/x86/cpu-features.c: Likewise.
* sysdeps/unix/sysv/linux/x86/dl-cet.h: Likewise.
* sysdeps/x86/cet-tunables.h: Likewise.
* sysdeps/x86/check-cet.awk: Likewise.
* sysdeps/x86/configure: Likewise.
* sysdeps/x86/configure.ac: Likewise.
* sysdeps/x86/dl-cet.c: Likewise.
* sysdeps/x86/dl-procruntime.c: Likewise.
* sysdeps/x86/dl-prop.h: Likewise.
* sysdeps/x86/libc-start.h: Likewise.
* sysdeps/x86/link_map.h: Likewise.
* sysdeps/i386/dl-trampoline.S (_dl_runtime_resolve): Add
_CET_ENDBR.
(_dl_runtime_profile): Likewise.
(_dl_runtime_resolve_shstk): New.
(_dl_runtime_profile_shstk): Likewise.
* sysdeps/linux/x86/Makefile (sysdep-dl-routines): Add dl-cet
if CET is enabled.
(CFLAGS-.o): Add -fcf-protection if CET is enabled.
(CFLAGS-.os): Likewise.
(CFLAGS-.op): Likewise.
(CFLAGS-.oS): Likewise.
(asm-CPPFLAGS): Add -fcf-protection -include cet.h if CET
is enabled.
(tests-special): Add $(objpfx)check-cet.out.
(cet-built-dso): New.
(+$(cet-built-dso:=.note)): Likewise.
(common-generated): Add $(cet-built-dso:$(common-objpfx)%=%.note).
($(objpfx)check-cet.out): New.
(generated): Add check-cet.out.
* sysdeps/x86/cpu-features.c: Include <dl-cet.h> and
<cet-tunables.h>.
(TUNABLE_CALLBACK (set_x86_ibt)): New prototype.
(TUNABLE_CALLBACK (set_x86_shstk)): Likewise.
(init_cpu_features): Call get_cet_status to check CET status
and update dl_x86_feature_1 with CET status. Call
TUNABLE_CALLBACK (set_x86_ibt) and TUNABLE_CALLBACK
(set_x86_shstk). Disable and lock CET in libc.a.
* sysdeps/x86/cpu-tunables.c: Include <cet-tunables.h>.
(TUNABLE_CALLBACK (set_x86_ibt)): New function.
(TUNABLE_CALLBACK (set_x86_shstk)): Likewise.
* sysdeps/x86/sysdep.h (_CET_NOTRACK): New.
(_CET_ENDBR): Define if not defined.
(ENTRY): Add _CET_ENDBR.
* sysdeps/x86/dl-tunables.list (glibc.tune): Add x86_ibt and
x86_shstk.
* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_resolve): Add
_CET_ENDBR.
(_dl_runtime_profile): Likewise.
This looks like a post-exploitation hardening measure: If an attacker is
able to redirect execution flow, they could use that to load a DSO which
contains additional code (or perhaps make the stack executable).
However, the checks are not in the correct place to be effective: If
they are performed before the critical operation, an attacker with
sufficient control over execution flow could simply jump directly to
the code which performs the operation, bypassing the check. The check
would have to be executed unconditionally after the operation and
terminate the process in case a caller violation was detected.
Furthermore, in _dl_check_caller, there was a fallback reading global
writable data (GL(dl_rtld_map).l_map_start and
GL(dl_rtld_map).l_text_end), which could conceivably be targeted by an
attacker to disable the check, too.
Other critical functions (such as system) remain completely
unprotected, so the value of these additional checks does not appear
that large. Therefore this commit removes this functionality.
Combine the four places where link maps are sorted into a single function.
This also moves the logic to skip the first map (representing the main
binary) to the callers.
Since __libc_multiple_libcs is defined as hidden symbol in init-first.c,
it should be always marked with attribute_hidden.
[BZ #18822]
* csu/libc-start.c (__libc_multiple_libcs): Removed.
* elf/dl-open.c: Include <libc-internal.h>.
(__libc_multiple_libcs): Removed.
* elf/dl-sysdep.c: Include <libc-internal.h> instead of
<hp-timing.h>.
* include/libc-internal.h (__libc_multiple_libcs): New.
* misc/sbrk.c: Include <libc-internal.h>.
(__libc_multiple_libcs): Removed.
This commit separates allocating and raising exceptions. This
simplifies catching and re-raising them because it is no longer
necessary to make a temporary, on-stack copy of the exception message.
The function _dl_addr_inside_object is simplified by removing
the conditional 'reladdr - l->l_phdr[n].p_vaddr >= 0' which is
always true. The function is refactored into it's own object file
and a unit test added to verify the correct behaviour of the
function.
The commit b632bdd3 moved the setting of the DF_1_NODELETE flag earlier
in the dl_open_worker function. However when calling dlopen with both
RTLD_NODELETE and RTLD_NOLOAD, the pointer returned by _dl_map_object is
NULL. This condition is checked just after setting the flag, while it
should be done before. Fix that.
Changelog:
[BZ #19810]
* elf/dl-open.c (dl_open_worker): Set DF_1_NODELETE flag later.
* elf/tst-noload.c: New test case.
* elf/Makefile (tests): Add tst-noload.
The DF_1_NODELETE flag is set too late when opening a DSO, due to
which, if a DSO is already open, subsequently opening it with
RTLD_NODELETE fails to set the DF_1_NODELETE flag. This patch fixes
this by setting the flag immediately after bumping the opencount.
Verified on x86_64.
[BZ #18676]
* elf/tst-nodelete-opened.c: New test case.
* elf/tst-nodelete-opened-lib.c: New test case module.
* elf/Makefile (tests, modules-names): Use them.
* elf/dl-open.c (dl_open_worker): Set DF_1_NODELETE flag
early.
https://sourceware.org/bugzilla/show_bug.cgi?id=17833
I've a shared library that contains both undefined and unique symbols.
Then I try to call the following sequence of dlopen:
1. dlopen("./libfoo.so", RTLD_NOW)
2. dlopen("./libfoo.so", RTLD_LAZY | RTLD_GLOBAL)
First dlopen call terminates with error because of undefined symbols,
but STB_GNU_UNIQUE ones set DF_1_NODELETE flag and hence block library
in the memory.
The library goes into inconsistent state as several structures remain
uninitialized. For instance, relocations for GOT table were not performed.
By the time of second dlopen call this library looks like as it would be
fully initialized but this is not true: any call through incorrect GOT
table leads to segmentation fault. On some systems this inconsistency
triggers assertions in the dynamic linker.
This patch adds a parameter to _dl_close_worker to implement forced object
deletion in case of dlopen() failure:
1. Clears DF_1_NODELETE bit if forced, to allow library to be removed from
memory.
2. For each unique symbol that is defined in this object clears
appropriate entry in _ns_unique_sym_table.
[BZ #17833]
* elf/Makefile (tests): Add tst-nodelete.
(modules-names): Add tst-nodelete-uniquemod.
(tst-nodelete-uniquemod.so-no-z-defs): New.
(tst-nodelete-rtldmod.so-no-z-defs): Likewise.
(tst-nodelete-zmod.so-no-z-defs): Likewise.
($(objpfx)tst-nodelete): Likewise.
($(objpfx)tst-nodelete.out): Likewise.
(LDFLAGS-tst-nodelete): Likewise.
(LDFLAGS-tst-nodelete-zmod.so): Likewise.
* elf/dl-close.c (_dl_close_worker): Add a parameter to
implement forced object deletion.
(_dl_close): Pass false to _dl_close_worker.
* elf/dl-open.c (_dl_open): Pass true to _dl_close_worker.
* elf/tst-nodelete.cc: New file.
* elf/tst-nodeletelib.cc: Likewise.
* elf/tst-znodeletelib.cc: Likewise.
* include/dlfcn.h (_dl_close_worker): Add a new parameter.
for ChangeLog
[BZ #17090]
[BZ #17620]
[BZ #17621]
[BZ #17628]
* NEWS: Update.
* elf/dl-tls.c (_dl_update_slotinfo): Clean up outdated DTV
entries with Static TLS too. Skip entries past the end of the
allocated DTV, from Alan Modra.
(tls_get_addr_tail): Update to glibc_likely/unlikely. Move
Static TLS DTV entry set up from...
(_dl_allocate_tls_init): ... here (fix modid assertion), ...
* elf/dl-reloc.c (_dl_nothread_init_static_tls): ... here...
* nptl/allocatestack.c (init_one_static_tls): ... and here...
* elf/dlopen.c (dl_open_worker): Drop l_tls_modid upper bound
for Static TLS.
* elf/tlsdeschtab.h (map_generation): Return size_t. Check
that the slot we find is associated with the given map before
using its generation count.
* nptl_db/db_info.c: Include ldsodefs.h.
(rtld_global, dtv_slotinfo_list, dtv_slotinfo): New typedefs.
* nptl_db/structs.def (DB_RTLD_VARIABLE): New macro.
(DB_MAIN_VARIABLE, DB_RTLD_GLOBAL_FIELD): Likewise.
(link_map::l_tls_offset): New struct field.
(dtv_t::counter): Likewise.
(rtld_global): New struct.
(_rtld_global): New rtld variable.
(dl_tls_dtv_slotinfo_list): New rtld global field.
(dtv_slotinfo_list): New struct.
(dtv_slotinfo): Likewise.
* nptl_db/td_symbol_list.c: Drop gnu/lib-names.h include.
(td_lookup): Rename to...
(td_mod_lookup): ... this. Use new mod parameter instead of
LIBPTHREAD_SO.
* nptl_db/td_thr_tlsbase.c: Include link.h.
(dtv_slotinfo_list, dtv_slotinfo): New functions.
(td_thr_tlsbase): Check DTV generation. Compute Static TLS
addresses even if the DTV is out of date or missing them.
* nptl_db/fetch-value.c (_td_locate_field): Do not refuse to
index zero-length arrays.
* nptl_db/thread_dbP.h: Include gnu/lib-names.h.
(td_lookup): Make it a macro implemented in terms of...
(td_mod_lookup): ... this declaration.
* nptl_db/db-symbols.awk (DB_RTLD_VARIABLE): Override.
(DB_MAIN_VARIABLE): Likewise.
The ability to recursively call dlopen is useful for malloc
implementations that wish to load other dynamic modules that
implement reentrant/AS-safe functions to use in their own
implementation.
Given that a user malloc implementation may be called by an
ongoing dlopen to allocate memory the user malloc
implementation interrupts dlopen and if it calls dlopen again
that's a reentrant call.
This patch fixes the issues with the ld.so.cache mapping
and the _r_debug assertion which prevent this from working
as expected.
See:
https://sourceware.org/ml/libc-alpha/2014-12/msg00446.html
This change creates a link map in static executables to serve as the
global search list for dlopen. It fixes a problem with the inability
to access the global symbol object and a crash on an attempt to map a
DSO into the global scope. Some code that has become dead after the
addition of this link map is removed too and test cases are provided.
Resolves: #15465
The program name may be unavailable if the user application tampers
with argc and argv[]. Some parts of the dynamic linker caters for
this while others don't, so this patch consolidates the check and
fallback into a single macro and updates all users.
The seen array was doubled in size recently, but the memset to clear
the array was not adjusted. We adjust the memset to always be correct
regardless of the size of seen.
---
2013-04-06 Carlos O'Donell <carlos@redhat.com>
[BZ #15309]
* elf/dl-open.c (dl_open_worker): memset all of seen array.
[BZ #13882]
* elf/dl-deps.c (_dl_map_object_deps): Fix cycle detection. Use
uint16_t for elements in the "seen" array to avoid char overflows.
* elf/dl-fini.c (_dl_sort_fini): Likewise.
* elf/dl-open.c (dl_open_worker): Likewise.
When dynamically loading a library along with several dependencies, calls to
_dl_add_to_slotinfo and _dl_update_slotinfo can become intermixed. As a
consequence, _dl_update_slotinfo will update the generation counter of the dtv
although not all of the slots belonging to that generation have been added.
Subsequent calls to _dl_add_to_slotinfo will add more slots to the same
generation, for which no storage will be allocated, as the dtv generation
checks will claim no work is necessary. This will lead to uninitialized dtv
entries and will likely cause a SIGSEGV when thread local variables are
accessed.
