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selftests/rseq: Uplift rseq selftests for compatibility with glibc-2.35

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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
This commit is contained in:
Mathieu Desnoyers 2022-01-24 12:12:45 -05:00 committed by Peter Zijlstra
parent 886ddfba93
commit 233e667e1a
3 changed files with 93 additions and 93 deletions
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2
tools/testing/selftests/rseq/Makefile
View File

@ -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.

169
tools/testing/selftests/rseq/rseq.c
View File

@ -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 = {
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;
/* Flags used during rseq registration. */
unsigned int rseq_flags;
static int rseq_ownership;
static
__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"))) = {
.cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
};
/*
* 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;
/* Whether this library have ownership of rseq registration. */
static int rseq_ownership;
static __thread volatile uint32_t __rseq_refcount;
static void signal_off_save(sigset_t *oldset)
{
sigset_t set;
int ret;
sigfillset(&set);
ret = pthread_sigmask(SIG_BLOCK, &set, oldset);
if (ret)
abort();
}
static void signal_restore(sigset_t oldset)
{
int ret;
ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
if (ret)
abort();
}
static int sys_rseq(volatile struct rseq_abi *rseq_abi, uint32_t rseq_len,
static int sys_rseq(struct rseq_abi *rseq_abi, uint32_t rseq_len,
int flags, uint32_t sig)
{
return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
}
int rseq_available(void)
{
int rc;
rc = sys_rseq(NULL, 0, 0, 0);
if (rc != -1)
abort();
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) {
if (rc)
return -1;
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;
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;
}

13
tools/testing/selftests/rseq/rseq.h
View File

@ -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)