[PATCH 5.15 68/98] selftests/rseq: Uplift rseq selftests for compatibility with glibc-2.35

Greg Kroah-Hartman
2022-07-05T12:25:58Z

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

commit 233e667e1ae3e348686bd9dd0172e62a09d852e1 upstream.

glibc-2.35 (upcoming release date 2022-02-01) exposes the rseq per-thread
data in the TCB, accessible at an offset from the thread pointer, rather
than through an actual Thread-Local Storage (TLS) variable, as the
Linux kernel selftests initially expected.

The __rseq_abi TLS and glibc-2.35's ABI for per-thread data cannot
actively coexist in a process, because the kernel supports only a single
rseq registration per thread.

Here is the scheme introduced to ensure selftests can work both with an
older glibc and with glibc-2.35+:

- librseq exposes its own "rseq_offset, rseq_size, rseq_flags" ABI.

- librseq queries for glibc rseq ABI (__rseq_offset, __rseq_size,
__rseq_flags) using dlsym() in a librseq library constructor. If those
are found, copy their values into rseq_offset, rseq_size, and
rseq_flags.

- Else, if those glibc symbols are not found, handle rseq registration
from librseq and use its own IE-model TLS to implement the rseq ABI
per-thread storage.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220124171253.22072-8-mathieu.desnoyers@efficios.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
tools/testing/selftests/rseq/Makefile | 2
tools/testing/selftests/rseq/rseq.c | 161 ++++++++++++++++------------------
tools/testing/selftests/rseq/rseq.h | 13 ++
3 files changed, 88 insertions(+), 88 deletions(-)

--- a/tools/testing/selftests/rseq/Makefile
+++ b/tools/testing/selftests/rseq/Makefile
@@ -6,7 +6,7 @@ endif

CFLAGS += -O2 -Wall -g -I./ -I../../../../usr/include/ -L$(OUTPUT) -Wl,-rpath=./ \
$(CLANG_FLAGS)
-LDLIBS += -lpthread
+LDLIBS += -lpthread -ldl

# Own dependencies because we only want to build against 1st prerequisite, but
# still track changes to header files and depend on shared object.
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -26,103 +26,113 @@
#include <assert.h>
#include <signal.h>
#include <limits.h>
+#include <dlfcn.h>

#include "../kselftest.h"
#include "rseq.h"

-__thread struct rseq_abi __rseq_abi = {
- .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
-};
+static const int *libc_rseq_offset_p;
+static const unsigned int *libc_rseq_size_p;
+static const unsigned int *libc_rseq_flags_p;
+
+/* Offset from the thread pointer to the rseq area. */
+int rseq_offset;
+
+/* Size of the registered rseq area. 0 if the registration was
+ unsuccessful. */
+unsigned int rseq_size = -1U;

-/*
- * Shared with other libraries. This library may take rseq ownership if it is
- * still 0 when executing the library constructor. Set to 1 by library
- * constructor when handling rseq. Set to 0 in destructor if handling rseq.
- */
-int __rseq_handled;
+/* Flags used during rseq registration. */
+unsigned int rseq_flags;

-/* Whether this library have ownership of rseq registration. */
static int rseq_ownership;

-static __thread volatile uint32_t __rseq_refcount;
+static
+__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"))) = {
+ .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
+};

-static void signal_off_save(sigset_t *oldset)
+static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len,
+ int flags, uint32_t sig)
{
- sigset_t set;
- int ret;
-
- sigfillset(&set);
- ret = pthread_sigmask(SIG_BLOCK, &set, oldset);
- if (ret)
- abort();
+ return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
}

-static void signal_restore(sigset_t oldset)
+int rseq_available(void)
{
- int ret;
+ int rc;

- ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
- if (ret)
+ rc = sys_rseq(NULL, 0, 0, 0);
+ if (rc != -1)
abort();
-}
-
-static int sys_rseq(volatile struct rseq_abi *rseq_abi, uint32_t rseq_len,
- int flags, uint32_t sig)
-{
- return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
+ switch (errno) {
+ case ENOSYS:
+ return 0;
+ case EINVAL:
+ return 1;
+ default:
+ abort();
+ }
}

int rseq_register_current_thread(void)
{
- int rc, ret = 0;
- sigset_t oldset;
+ int rc;

- if (!rseq_ownership)
+ if (!rseq_ownership) {
+ /* Treat libc's ownership as a successful registration. */
return 0;
- signal_off_save(&oldset);
- if (__rseq_refcount == UINT_MAX) {
- ret = -1;
- goto end;
}
- if (__rseq_refcount++)
- goto end;
rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), 0, RSEQ_SIG);
- if (!rc) {
- assert(rseq_current_cpu_raw() >= 0);
- goto end;
- }
- if (errno != EBUSY)
- RSEQ_WRITE_ONCE(__rseq_abi.cpu_id, RSEQ_ABI_CPU_ID_REGISTRATION_FAILED);
- ret = -1;
- __rseq_refcount--;
-end:
- signal_restore(oldset);
- return ret;
+ if (rc)
+ return -1;
+ assert(rseq_current_cpu_raw() >= 0);
+ return 0;
}

int rseq_unregister_current_thread(void)
{
- int rc, ret = 0;
- sigset_t oldset;
+ int rc;

- if (!rseq_ownership)
+ if (!rseq_ownership) {
+ /* Treat libc's ownership as a successful unregistration. */
return 0;
- signal_off_save(&oldset);
- if (!__rseq_refcount) {
- ret = -1;
- goto end;
}
- if (--__rseq_refcount)
- goto end;
- rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi),
- RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
- if (!rc)
- goto end;
- __rseq_refcount = 1;
- ret = -1;
-end:
- signal_restore(oldset);
- return ret;
+ rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+ if (rc)
+ return -1;
+ return 0;
+}
+
+static __attribute__((constructor))
+void rseq_init(void)
+{
+ libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset");
+ libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size");
+ libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags");
+ if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p) {
+ /* rseq registration owned by glibc */
+ rseq_offset = *libc_rseq_offset_p;
+ rseq_size = *libc_rseq_size_p;
+ rseq_flags = *libc_rseq_flags_p;
+ return;
+ }
+ if (!rseq_available())
+ return;
+ rseq_ownership = 1;
+ rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
+ rseq_size = sizeof(struct rseq_abi);
+ rseq_flags = 0;
+}
+
+static __attribute__((destructor))
+void rseq_exit(void)
+{
+ if (!rseq_ownership)
+ return;
+ rseq_offset = 0;
+ rseq_size = -1U;
+ rseq_ownership = 0;
}

int32_t rseq_fallback_current_cpu(void)
@@ -136,20 +146,3 @@ int32_t rseq_fallback_current_cpu(void)
}
return cpu;
}
-
-void __attribute__((constructor)) rseq_init(void)
-{
- /* Check whether rseq is handled by another library. */
- if (__rseq_handled)
- return;
- __rseq_handled = 1;
- rseq_ownership = 1;
-}
-
-void __attribute__((destructor)) rseq_fini(void)
-{
- if (!rseq_ownership)
- return;
- __rseq_handled = 0;
- rseq_ownership = 0;
-}
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -43,12 +43,19 @@
#define RSEQ_INJECT_FAILED
#endif

-extern __thread struct rseq_abi __rseq_abi;
-extern int __rseq_handled;
+#include "rseq-thread-pointer.h"
+
+/* Offset from the thread pointer to the rseq area. */
+extern int rseq_offset;
+/* Size of the registered rseq area. 0 if the registration was
+ unsuccessful. */
+extern unsigned int rseq_size;
+/* Flags used during rseq registration. */
+extern unsigned int rseq_flags;

static inline struct rseq_abi *rseq_get_abi(void)
{
- return &__rseq_abi;
+ return (struct rseq_abi *) ((uintptr_t) rseq_thread_pointer() + rseq_offset);
}

#define rseq_likely(x) __builtin_expect(!!(x), 1)