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From the bug report [1], multiple programs still require to dlopen
shared libraries with either missing PT_GNU_STACK or with the executable
bit set. Although, in some cases, it seems to be a hard-craft assembly
source without the required .note.GNU-stack marking (so the static linker
is forced to set the stack executable if the ABI requires it), other
cases seem that the library uses trampolines [2].
Unfortunately, READ_IMPLIES_EXEC is not an option since on some ABIs
(x86_64), the kernel clears the bit, making it unsupported. To avoid
reinstating the broken code that changes stack permission on dlopen
(0ca8785a28), this patch extends the glibc.rtld.execstack tunable to
allow an option to force an executable stack at the program startup.
The tunable is a security issue because it defeats the PT_GNU_STACK
hardening. It has the slight advantage of making it explicit by the
caller, and, as for other tunables, this is disabled for setuid binaries.
A tunable also allows us to eventually remove it, but from previous
experiences, it would require some time.
Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu.
[1] https://sourceware.org/bugzilla/show_bug.cgi?id=32653
[2] https://github.com/conda-forge/ctng-compiler-activation-feedstock/issues/143
Reviewed-by: Sam James <sam@gentoo.org>
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Checked on aarch64-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
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The tst-origin test must link against liborigin-mod.so. Correct
build order depends on a makefile rule dependency on
$(objpfx)liborigin-mod.so. Use +nolink-deps to remvoe this
dependency from the linker command line.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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The 7bb8045ec0 path made the '%n' fortify check ignore EMFILE errors
while trying to open /proc/self/maps, and this added a security
issue where EMFILE can be attacker-controlled thus making it
ineffective for some cases.
The EMFILE failure is reinstated but with a different error
message. Also, to improve the false positive of the hardening for
the cases where no new files can be opened, the
_dl_readonly_area now uses _dl_find_object to check if the
memory area is within a writable ELF segment. The procfs method is
still used as fallback.
Checked on x86_64-linux-gnu and i686-linux-gnu.
Reviewed-by: Arjun Shankar <arjun@redhat.com>
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The tst-origin build can fail with:
/usr/bin/ld: [...]libc.so: undefined reference to `__tunable_is_initialized@GLIBC_PRIVATE'
Since the custom link invocation links against system glibc instead
of the built one.
The only requirement is to avoid liborigin.so linked with a full path,
which is the default for --enable-hardcoded-path-in-tests. There
is no need to use a custom rule.
Checked on x86_64-linux-gnu.
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Add tests-special before include Rules and compile liborigin.os with
MODULE_NAME set to testsuite instead of libc.
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When an executable is invoked directly, we calculate $ORIGIN by calling
readlink on /proc/self/exe, which the Linux kernel resolves to the
target of any symlinks. However, if an executable is run through ld.so,
we cannot use /proc/self/exe and instead use the path given as an
argument. This leads to a different calculation of $ORIGIN, which is
most notable in that it causes ldd to behave differently (e.g., by not
finding a library) from directly running the program.
To make the behavior consistent, take advantage of the fact that the
kernel also resolves /proc/self/fd/ symlinks to the target of any
symlinks in the same manner, so once we have opened the main executable
in order to load it, replace the user-provided path with the result of
calling readlink("/proc/self/fd/N").
(On non-Linux platforms this resolution does not happen and so no
behavior change is needed.)
The __fd_to_filename requires _fitoa_word and _itoa_word, which for
32-bits pulls a lot of definitions from _itoa.c (due _ITOA_NEEDED
being defined). To simplify the build move the required function
to a new file, _fitoa_word.c.
Checked on x86_64-linux-gnu and i686-linux-gnu.
Co-authored-by: Geoffrey Thomas <geofft@ldpreload.com>
Reviewed-by: Geoffrey Thomas <geofft@ldpreload.com>
Tested-by: Geoffrey Thomas <geofft@ldpreload.com>
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This call must not complete initialization of all shared objects
in the global scope because the ELF constructor which makes the call
likely has not finished initialization. Calling more constructors
at this point would expose those to a partially constructed
dependency.
This completes the revert of commit 9897ced8e78db5d813166a7ccccfd5a
("elf: Run constructors on cyclic recursive dlopen (bug 31986)").
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This was found through code inspection. No application impact is
known.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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The BZ #32763 tests fail to build for MicroBlaze (which defines
MAX_OFILE_ALIGNMENT to (32768*8) in GCC, so __attribute__ ((aligned
(65536))) is unsupported). Add a configure-time check to enable BZ #32763
tests only if __attribute__ ((aligned (65536))) is supported.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>
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As shown in
https://sourceware.org/bugzilla/show_bug.cgi?id=25237
linker may generate an empty PT_LOAD segments at offset 0:
Elf file type is EXEC (Executable file)
Entry point 0x4000e8
There are 3 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000400000 0x0000000000400000
0x00000000000000f0 0x00000000000000f0 R E 0x1000
LOAD 0x0000000000000000 0x0000000000410000 0x0000000000410000
0x0000000000000000 0x0000000000b5dce8 RW 0x10000
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 0x10
Section to Segment mapping:
Segment Sections...
00 .text
01 .bss
02
Skip the empty PT_LOAD segment at offset 0 to support such binaries.
This fixes BZ #32763.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>
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When GNU Binutils is configured with --enable-error-execstack=yes, a handful
of our tests which rely on -Wl,-z,execstack fail. Pass --Wl,--no-error-execstack
to override the behaviour and get a warning instead.
Bug: https://sourceware.org/PR32717
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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If an auditor loads many TLS-using modules during startup, it is
possible to trigger DTV resizing. Previously, the DTV was marked
as allocated by the main malloc afterwards, even if the minimal
malloc was still in use. With this change, _dl_resize_dtv marks
the resized DTV as allocated with the minimal malloc.
The new test reuses TLS-using modules from other auditing tests.
Reviewed-by: DJ Delorie <dj@redhat.com>
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This reduces code size and dependencies on ld.so internals from
libc.so.
Fixes commit f4c142bb9fe6b02c0af8cfca8a920091e2dba44b
("arm: Use _dl_find_object on __gnu_Unwind_Find_exidx (BZ 31405)").
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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This will be needed to compute __rseq_offset outside of the TLS
relocation machinery.
Reviewed-by: Michael Jeanson <mjeanson@efficios.com>
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On 32-bit Arm, -fasynchronous-unwind-tables creates a reference
to the symbol __aeabi_unwind_cpp_pr0. Compile the tests without
this flag even if it is passed as part of CC, to avoid linker
failures.
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Commit 8f8dd904c4a2207699bb666f30acceb5209c8d3f (“elf:
rtld_multiple_ref is always true”) removed some code that happened
to enable compatibility with programs that do not link against
libc.so. Such programs cannot call dlopen or any dynamic linker
functions (except __tls_get_addr), so this is not really useful.
Still ld.so should not crash with a null-pointer dereference
or undefined symbol reference in these cases.
In the main relocation loop, call _dl_relocate_object unconditionally
because it already checks if the object has been relocated.
If libc.so was loaded, self-relocate ld.so against it and call
__rtld_mutex_init and __rtld_malloc_init_real to activate the full
implementations. Those are available only if libc.so is there,
so skip these initialization steps if libc.so is absent. Without
libc.so, the global scope can be completely empty. This can cause
ld.so self-relocation to fail because if it uses symbol-based
relocations, which is why the second ld.so self-relocation is not
performed if libc.so is missing.
The previous concern regarding GOT updates through self-relocation
no longer applies because function pointers are updated
explicitly through __rtld_mutex_init and __rtld_malloc_init_real,
and not through relocation. However, the second ld.so self-relocation
is still delayed, in case there are other symbols being used.
Fixes commit 8f8dd904c4a2207699bb666f30acceb5209c8d3f (“elf:
rtld_multiple_ref is always true”).
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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Since have-mtls-descriptor is only used for glibc testing, rename it to
have-test-mtls-descriptor. Also enable tst-gnu2-tls2-amx only if
$(have-test-mtls-descriptor) == gnu2.
Tested with GCC 14 and Clang 19/18/17 on x86-64.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>
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The new tunable can be used to control whether executable stacks are
allowed from either the main program or dependencies. The default is
to allow executable stacks.
The executable stacks default permission is checked agains the one
provided by the PT_GNU_STACK from program headers (if present). The
tunable also disables the stack permission change if any dependency
requires an executable stack at loading time.
Checked on x86_64-linux-gnu, i686-linux-gnu, and aarch64-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
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Similar to tst-execstack-prog, check if executable stacks works for
statically linked programs.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
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tst-dlopen-nodelete-reloc requires STB_GNU_UNIQUE support so that NODELETE
is propagated by do_lookup_unique. Enable it only if TEST_CXX supports
STB_GNU_UNIQUE,
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>
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Compiler may default to -fno-semantic-interposition. But some elf test
modules must be compiled with -fsemantic-interposition to function properly.
Add a TEST_CC check for -fsemantic-interposition and use it on elf test
modules. This fixed
FAIL: elf/tst-dlclose-lazy
FAIL: elf/tst-pie1
FAIL: elf/tst-plt-rewrite1
FAIL: elf/unload4
when Clang 19 is used to test glibc.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>
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Since trampoline is required to test execstack, enable execstack tests
only if compiler supports trampoline.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>
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The current DSO dependency sorting tests are for a limited number of
specific cases, including some from particular bug reports.
Add tests that systematically cover all possible DAGs for an
executable and the shared libraries it depends on, directly or
indirectly, up to four objects (an executable and three shared
libraries). (For this kind of DAG - ones with a single source vertex
from which all others are reachable, and an ordering on the edges from
each vertex - there are 57 DAGs on four vertices, 3399 on five
vertices and 1026944 on six vertices; see
https://arxiv.org/pdf/2303.14710 for more details on this enumeration.
I've tested that the 3399 cases with five vertices do all pass if
enabled.)
These tests are replicating the sorting logic from the dynamic linker
(thereby, for example, asserting that it doesn't accidentally change);
I'm not claiming that the logic in the dynamic linker is in some
abstract sense optimal. Note that these tests do illustrate how in
some cases the two sorting algorithms produce different results for a
DAG (I think all the existing tests for such differences are ones
involving cycles, and the motivation for the new algorithm was also to
improve the handling of cycles):
tst-dso-ordering-all4-44: a->[bc];{}->[cba]
output(glibc.rtld.dynamic_sort=1): c>b>a>{}<a<b<c
output(glibc.rtld.dynamic_sort=2): b>c>a>{}<a<c<b
They also illustrate that sometimes the sorting algorithms do not
follow the order in which dependencies are listed in DT_NEEDED even
though there is a valid topological sort that does follow that, which
might be counterintuitive considering that the DT_NEEDED ordering is
followed in the simplest cases:
tst-dso-ordering-all4-56: {}->[abc]
output: c>b>a>{}<a<b<c
shows such a simple case following DT_NEEDED order for destructor
execution (the reverse of it for constructor execution), but
tst-dso-ordering-all4-41: a->[cb];{}->[cba]
output: c>b>a>{}<a<b<c
shows that c and b are in the opposite order to what might be expected
from the simplest case, though there is no dependency requiring such
an opposite order to be used.
(I'm not asserting that either of those things is a problem, simply
observing them as less obvious properties of the sorting algorithms
shown up by these tests.)
Tested for x86_64.
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The postclean-generated setting in elf/Makefile lists
$(objpfx)/dso-sort-tests-2.generated-makefile twice and
$(objpfx)/dso-sort-tests-1.generated-makefile not at all, which looks
like a typo; fix it to list each once.
Tested for x86_64.
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Add an additional test of TLS variables, with different alignment,
accessed from different modules. The idea of the alignment test is
similar to tst-tlsalign and the same code is shared for setting up
test variables, but unlike the tst-tlsalign code, there are multiple
threads and variables are accessed from multiple objects to verify
that they get a consistent notion of the address of an object within a
thread. Threads are repeatedly created and shut down to verify proper
initialization in each new thread. The test is also repeated with TLS
descriptors when supported. (However, only initial-exec TLS is
covered in this test.)
Tested for x86_64.
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Add tests that the dynamic linker works correctly with symbol names
involving hash collisions, for both choices of hash style (and
--hash-style=both as well). I note that there weren't actually any
previous tests using --hash-style (so tests would only cover the
default linker configuration in that regard). Also test symbol
versions involving hash collisions.
Tested for x86_64.
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For a static PIE with non-zero load address, its PT_DYNAMIC segment
entries contain the relocated values for the load address in static PIE.
Since static PIE usually doesn't have PT_PHDR segment, use p_vaddr of
the PT_LOAD segment with offset == 0 as the load address in static PIE
and adjust the entries of PT_DYNAMIC segment in static PIE by properly
setting the l_addr field for static PIE. This fixes BZ #31799.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
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Before commit ee1ada1bdb8074de6e1bdc956ab19aef7b6a7872
("elf: Rework exception handling in the dynamic loader
[BZ #25486]"), the previous order called the main calloc
to allocate a shadow GOT/PLT array for auditing support.
This happened before libc.so.6 ELF constructors were run, so
a user malloc could run without libc.so.6 having been
initialized fully. One observable effect was that
environ was NULL at this point.
It does not seem to be possible at present to trigger such
an allocation, but it seems more robust to delay switching
to main malloc after ld.so self-relocation is complete.
The elf/tst-rtld-no-malloc-audit test case fails with a
2.34-era glibc that does not have this fix.
Reviewed-by: DJ Delorie <dj@redhat.com>
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This reverts commit 9897ced8e78db5d813166a7ccccfd5a42c69ef20.
Adjust the test expectations in elf/tst-dlopen-auditdup-auditmod.c
accordingly.
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Previously, a la_activity audit event was generated before
relocation processing completed. This does did not match what
happened during initial startup in elf/rtld.c (towards the end
of dl_main). It also caused various problems if an auditor
tried to open the same shared object again using dlmopen:
If it was the directly loaded object, it had a search scope
associated with it, so the early exit in dl_open_worker_begin
was taken even though the object was unrelocated. This caused
the r_state == RT_CONSISTENT assert to fail. Avoidance of the
assert also depends on reversing the order of r_state update
and auditor event (already implemented in a previous commit).
At the later point, args->map can be NULL due to failure,
so use the assigned namespace ID instead if that is available.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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This is conceptually similar to the reported bug, but does not
depend on auditing. The fix is simple: just complete execution
of the constructors. This exposed the fact that the link map
for statically linked executables does not have l_init_called
set, even though constructors have run.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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Add new testcase elf/tst-startup-errno.c which tests that errno is set
to 0 at first ELF constructor execution and at the start of the
program's main function.
Tested for x86_64
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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Fixes commit 5097cd344fd243fb8deb6dec96e8073753f962f9
("elf: Avoid re-initializing already allocated TLS in dlopen
(bug 31717)").
Reported-by: Patsy Griffin <patsy@redhat.com>
Reviewed-by: Patsy Griffin <patsy@redhat.com>
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The current racy approach is to enable asynchronous cancellation
before making the syscall and restore the previous cancellation
type once the syscall returns, and check if cancellation has happen
during the cancellation entrypoint.
As described in BZ#12683, this approach shows 2 problems:
1. Cancellation can act after the syscall has returned from the
kernel, but before userspace saves the return value. It might
result in a resource leak if the syscall allocated a resource or a
side effect (partial read/write), and there is no way to program
handle it with cancellation handlers.
2. If a signal is handled while the thread is blocked at a cancellable
syscall, the entire signal handler runs with asynchronous
cancellation enabled. This can lead to issues if the signal
handler call functions which are async-signal-safe but not
async-cancel-safe.
For the cancellation to work correctly, there are 5 points at which the
cancellation signal could arrive:
[ ... )[ ... )[ syscall ]( ...
1 2 3 4 5
1. Before initial testcancel, e.g. [*... testcancel)
2. Between testcancel and syscall start, e.g. [testcancel...syscall start)
3. While syscall is blocked and no side effects have yet taken
place, e.g. [ syscall ]
4. Same as 3 but with side-effects having occurred (e.g. a partial
read or write).
5. After syscall end e.g. (syscall end...*]
And libc wants to act on cancellation in cases 1, 2, and 3 but not
in cases 4 or 5. For the 4 and 5 cases, the cancellation will eventually
happen in the next cancellable entrypoint without any further external
event.
The proposed solution for each case is:
1. Do a conditional branch based on whether the thread has received
a cancellation request;
2. It can be caught by the signal handler determining that the saved
program counter (from the ucontext_t) is in some address range
beginning just before the "testcancel" and ending with the
syscall instruction.
3. SIGCANCEL can be caught by the signal handler and determine that
the saved program counter (from the ucontext_t) is in the address
range beginning just before "testcancel" and ending with the first
uninterruptable (via a signal) syscall instruction that enters the
kernel.
4. In this case, except for certain syscalls that ALWAYS fail with
EINTR even for non-interrupting signals, the kernel will reset
the program counter to point at the syscall instruction during
signal handling, so that the syscall is restarted when the signal
handler returns. So, from the signal handler's standpoint, this
looks the same as case 2, and thus it's taken care of.
5. For syscalls with side-effects, the kernel cannot restart the
syscall; when it's interrupted by a signal, the kernel must cause
the syscall to return with whatever partial result is obtained
(e.g. partial read or write).
6. The saved program counter points just after the syscall
instruction, so the signal handler won't act on cancellation.
This is similar to 4. since the program counter is past the syscall
instruction.
So The proposed fixes are:
1. Remove the enable_asynccancel/disable_asynccancel function usage in
cancellable syscall definition and instead make them call a common
symbol that will check if cancellation is enabled (__syscall_cancel
at nptl/cancellation.c), call the arch-specific cancellable
entry-point (__syscall_cancel_arch), and cancel the thread when
required.
2. Provide an arch-specific generic system call wrapper function
that contains global markers. These markers will be used in
SIGCANCEL signal handler to check if the interruption has been
called in a valid syscall and if the syscalls has side-effects.
A reference implementation sysdeps/unix/sysv/linux/syscall_cancel.c
is provided. However, the markers may not be set on correct
expected places depending on how INTERNAL_SYSCALL_NCS is
implemented by the architecture. It is expected that all
architectures add an arch-specific implementation.
3. Rewrite SIGCANCEL asynchronous handler to check for both canceling
type and if current IP from signal handler falls between the global
markers and act accordingly.
4. Adjust libc code to replace LIBC_CANCEL_ASYNC/LIBC_CANCEL_RESET to
use the appropriate cancelable syscalls.
5. Adjust 'lowlevellock-futex.h' arch-specific implementations to
provide cancelable futex calls.
Some architectures require specific support on syscall handling:
* On i386 the syscall cancel bridge needs to use the old int80
instruction because the optimized vDSO symbol the resulting PC value
for an interrupted syscall points to an address outside the expected
markers in __syscall_cancel_arch. It has been discussed in LKML [1]
on how kernel could help userland to accomplish it, but afaik
discussion has stalled.
Also, sysenter should not be used directly by libc since its calling
convention is set by the kernel depending of the underlying x86 chip
(check kernel commit 30bfa7b3488bfb1bb75c9f50a5fcac1832970c60).
* mips o32 is the only kABI that requires 7 argument syscall, and to
avoid add a requirement on all architectures to support it, mips
support is added with extra internal defines.
Checked on aarch64-linux-gnu, arm-linux-gnueabihf, powerpc-linux-gnu,
powerpc64-linux-gnu, powerpc64le-linux-gnu, i686-linux-gnu, and
x86_64-linux-gnu.
[1] https://lkml.org/lkml/2016/3/8/1105
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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The old code used l_init_called as an indicator for whether TLS
initialization was complete. However, it is possible that
TLS for an object is initialized, written to, and then dlopen
for this object is called again, and l_init_called is not true at
this point. Previously, this resulted in TLS being initialized
twice, discarding any interim writes (technically introducing a
use-after-free bug even).
This commit introduces an explicit per-object flag, l_tls_in_slotinfo.
It indicates whether _dl_add_to_slotinfo has been called for this
object. This flag is used to avoid double-initialization of TLS.
In update_tls_slotinfo, the first_static_tls micro-optimization
is removed because preserving the initalization flag for subsequent
use by the second loop for static TLS is a bit complicated, and
another per-object flag does not seem to be worth it. Furthermore,
the l_init_called flag is dropped from the second loop (for static
TLS initialization) because l_need_tls_init on its own prevents
double-initialization.
The remaining l_init_called usage in resize_scopes and update_scopes
is just an optimization due to the use of scope_has_map, so it is
not changed in this commit.
The isupper check ensures that libc.so.6 is TLS is not reverted.
Such a revert happens if l_need_tls_init is not cleared in
_dl_allocate_tls_init for the main_thread case, now that
l_init_called is not checked anymore in update_tls_slotinfo
in elf/dl-open.c.
Reported-by: Jonathon Anderson <janderson@rice.edu>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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