While implementing rseq selftest for s390 a glibc problem with tls
variables alignment has been discovered. It turned out to be a general
problem affecting several architectures. The bug opened for this problem:
https://sourceware.org/bugzilla/show_bug.cgi?id=23403
There is no fix yet. On s390 __rseq_abi ends up aligned to 0x10 instead
of 0x20 which makes rseq selftest fail every time.
The change proposed adds __rseq_abi misalignment check, produces user
friendly message and skips the test.
Vasily Gorbik (1):
rseq/selftests: add __rseq_abi misalignment check
tools/testing/selftests/rseq/rseq.c | 19 +++++++++++++++++++
.../testing/selftests/rseq/run_param_test.sh | 4 ++--
2 files changed, 21 insertions(+), 2 deletions(-)
--
2.18.0.13.gd42ae10
The kernel rseq syscall expects that struct rseq is 32 bytes aligned and
returns EINVAL otherwise. Even though __rseq_abi is declared as static
and proper aligned attribute is present __rseq_abi is a part of thread
local storage. It turns out that on some platforms TLS itself is not
properly aligned (at least for threads created), which is a glibc nptl
bug and should be eventually fixed and backported. But in a meanwhile
add __rseq_abi misalignment check, which would detect this situation
and skip rseq test with some user friendly message.
glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23403
Signed-off-by: Vasily Gorbik <[email protected]>
---
tools/testing/selftests/rseq/rseq.c | 19 +++++++++++++++++++
.../testing/selftests/rseq/run_param_test.sh | 4 ++--
2 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..50b13318395a 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -64,6 +64,23 @@ static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
}
+/*
+ * rseq syscall might fail on some platforms due to wrong alignment of TLS
+ * variables:
+ * https://sourceware.org/bugzilla/show_bug.cgi?id=23403
+ *
+ * check if glibc bug is present and skip the test in this case
+ */
+static void assert_rseq_abi_aligned()
+{
+ if ((unsigned long)&__rseq_abi & (__alignof__(__rseq_abi) - 1)) {
+ fputs("__rseq_abi is not properly aligned, which is a known \n"
+ "glibc nptl bug (https://sourceware.org/bugzilla/show_bug.cgi?id=23403).\n"
+ "You need a fixed version of glibc to run this test.\n", stderr);
+ exit(4); /* skip this test */
+ }
+}
+
int rseq_register_current_thread(void)
{
int rc, ret = 0;
@@ -72,6 +89,7 @@ int rseq_register_current_thread(void)
signal_off_save(&oldset);
if (refcount++)
goto end;
+ assert_rseq_abi_aligned();
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
if (!rc) {
assert(rseq_current_cpu_raw() >= 0);
@@ -94,6 +112,7 @@ int rseq_unregister_current_thread(void)
signal_off_save(&oldset);
if (--refcount)
goto end;
+ assert_rseq_abi_aligned();
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
if (!rc)
diff --git a/tools/testing/selftests/rseq/run_param_test.sh b/tools/testing/selftests/rseq/run_param_test.sh
index 3acd6d75ff9f..56caf5e3de3e 100755
--- a/tools/testing/selftests/rseq/run_param_test.sh
+++ b/tools/testing/selftests/rseq/run_param_test.sh
@@ -34,9 +34,9 @@ function do_tests()
local i=0
while [ "$i" -lt "${#TEST_LIST[@]}" ]; do
echo "Running test ${TEST_NAME[$i]}"
- ./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+ ./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
echo "Running compare-twice test ${TEST_NAME[$i]}"
- ./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+ ./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
let "i++"
done
}
--
2.18.0.13.gd42ae10
The kernel rseq syscall expects that struct rseq is 32 bytes aligned and
returns EINVAL otherwise. Even though __rseq_abi is declared as static
and proper aligned attribute is present __rseq_abi is a part of thread
local storage. It turns out that on some platforms TLS itself is not
properly aligned (at least for threads created), which is a glibc nptl
bug and should be eventually fixed and backported. But in a meanwhile
add __rseq_abi misalignment check, which would detect this situation
and skip rseq test with some user friendly message.
glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23403
Signed-off-by: Vasily Gorbik <[email protected]>
---
tools/testing/selftests/rseq/rseq.c | 20 +++++++++++++++++++
.../testing/selftests/rseq/run_param_test.sh | 4 ++--
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..3de7f0e7442e 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -64,6 +64,24 @@ static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
}
+/*
+ * rseq syscall might fail on some platforms due to wrong alignment of TLS
+ * variables:
+ * https://sourceware.org/bugzilla/show_bug.cgi?id=23403
+ *
+ * check if glibc bug is present and skip the test in this case
+ */
+static void assert_rseq_abi_aligned(void)
+{
+ if ((unsigned long)&__rseq_abi & (__alignof__(__rseq_abi) - 1)) {
+ fputs("__rseq_abi is not properly aligned, which is a known\n"
+ "glibc nptl bug (https://sourceware.org/bugzilla/show_bug.cgi?id=23403).\n"
+ "You need a fixed version of glibc to run this test.\n",
+ stderr);
+ exit(4); /* skip this test */
+ }
+}
+
int rseq_register_current_thread(void)
{
int rc, ret = 0;
@@ -72,6 +90,7 @@ int rseq_register_current_thread(void)
signal_off_save(&oldset);
if (refcount++)
goto end;
+ assert_rseq_abi_aligned();
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
if (!rc) {
assert(rseq_current_cpu_raw() >= 0);
@@ -94,6 +113,7 @@ int rseq_unregister_current_thread(void)
signal_off_save(&oldset);
if (--refcount)
goto end;
+ assert_rseq_abi_aligned();
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
if (!rc)
diff --git a/tools/testing/selftests/rseq/run_param_test.sh b/tools/testing/selftests/rseq/run_param_test.sh
index 3acd6d75ff9f..56caf5e3de3e 100755
--- a/tools/testing/selftests/rseq/run_param_test.sh
+++ b/tools/testing/selftests/rseq/run_param_test.sh
@@ -34,9 +34,9 @@ function do_tests()
local i=0
while [ "$i" -lt "${#TEST_LIST[@]}" ]; do
echo "Running test ${TEST_NAME[$i]}"
- ./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+ ./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
echo "Running compare-twice test ${TEST_NAME[$i]}"
- ./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+ ./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
let "i++"
done
}
--
2.18.0.13.gd42ae10
On Mon, Aug 06, 2018 at 03:27:23PM +0200, Vasily Gorbik wrote:
> The kernel rseq syscall expects that struct rseq is 32 bytes aligned and
> returns EINVAL otherwise. Even though __rseq_abi is declared as static
> and proper aligned attribute is present __rseq_abi is a part of thread
> local storage. It turns out that on some platforms TLS itself is not
> properly aligned (at least for threads created), which is a glibc nptl
> bug and should be eventually fixed and backported. But in a meanwhile
> add __rseq_abi misalignment check, which would detect this situation
> and skip rseq test with some user friendly message.
>
> glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23403
>
> Signed-off-by: Vasily Gorbik <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
> ---
> tools/testing/selftests/rseq/rseq.c | 20 +++++++++++++++++++
> .../testing/selftests/rseq/run_param_test.sh | 4 ++--
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
> index 4847e97ed049..3de7f0e7442e 100644
> --- a/tools/testing/selftests/rseq/rseq.c
> +++ b/tools/testing/selftests/rseq/rseq.c
> @@ -64,6 +64,24 @@ static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
> return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
> }
>
> +/*
> + * rseq syscall might fail on some platforms due to wrong alignment of TLS
> + * variables:
> + * https://sourceware.org/bugzilla/show_bug.cgi?id=23403
> + *
> + * check if glibc bug is present and skip the test in this case
> + */
> +static void assert_rseq_abi_aligned(void)
> +{
> + if ((unsigned long)&__rseq_abi & (__alignof__(__rseq_abi) - 1)) {
> + fputs("__rseq_abi is not properly aligned, which is a known\n"
> + "glibc nptl bug (https://sourceware.org/bugzilla/show_bug.cgi?id=23403).\n"
> + "You need a fixed version of glibc to run this test.\n",
> + stderr);
> + exit(4); /* skip this test */
> + }
> +}
> +
> int rseq_register_current_thread(void)
> {
> int rc, ret = 0;
> @@ -72,6 +90,7 @@ int rseq_register_current_thread(void)
> signal_off_save(&oldset);
> if (refcount++)
> goto end;
> + assert_rseq_abi_aligned();
> rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
> if (!rc) {
> assert(rseq_current_cpu_raw() >= 0);
> @@ -94,6 +113,7 @@ int rseq_unregister_current_thread(void)
> signal_off_save(&oldset);
> if (--refcount)
> goto end;
> + assert_rseq_abi_aligned();
> rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
> RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
> if (!rc)
> diff --git a/tools/testing/selftests/rseq/run_param_test.sh b/tools/testing/selftests/rseq/run_param_test.sh
> index 3acd6d75ff9f..56caf5e3de3e 100755
> --- a/tools/testing/selftests/rseq/run_param_test.sh
> +++ b/tools/testing/selftests/rseq/run_param_test.sh
> @@ -34,9 +34,9 @@ function do_tests()
> local i=0
> while [ "$i" -lt "${#TEST_LIST[@]}" ]; do
> echo "Running test ${TEST_NAME[$i]}"
> - ./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
> + ./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
> echo "Running compare-twice test ${TEST_NAME[$i]}"
> - ./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
> + ./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
> let "i++"
> done
> }
> --
> 2.18.0.13.gd42ae10
----- On Aug 6, 2018, at 7:47 AM, gor [email protected] wrote:
> While implementing rseq selftest for s390 a glibc problem with tls
> variables alignment has been discovered. It turned out to be a general
> problem affecting several architectures. The bug opened for this problem:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=23403
>
> There is no fix yet. On s390 __rseq_abi ends up aligned to 0x10 instead
> of 0x20 which makes rseq selftest fail every time.
>
> The change proposed adds __rseq_abi misalignment check, produces user
> friendly message and skips the test.
That's a very unfortunate situation. I'm concerned about adding glibc-specific
error messages in rseq selftests though. I'm curious to hear what others think
about this.
I would have thought simply improving rseq registration error handling from
having the test program return nonzero to add a perror() in there would be
a more generic way to handle this.
Regarding the message printed by your check: "you need a fixed version of glibc to
run this test". I disagree with it. Someone can effectively run the test on
a bogus glibc and it serves its purpose: it reports that glibc is buggy.
I would understand adding this kind of test in an user-facing application or
library to detect bogus glibc (in fact I've used similar approaches in lttng-ust
to detect bogus compilers), but why add this to skip a selftest program, which
sole purpose is to test the stack underneath it ?
Thanks,
Mathieu
>
> Vasily Gorbik (1):
> rseq/selftests: add __rseq_abi misalignment check
>
> tools/testing/selftests/rseq/rseq.c | 19 +++++++++++++++++++
> .../testing/selftests/rseq/run_param_test.sh | 4 ++--
> 2 files changed, 21 insertions(+), 2 deletions(-)
>
> --
> 2.18.0.13.gd42ae10
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com