Use the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE to detect the RSEQ
features supported by the kernel.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
tools/testing/selftests/rseq/rseq-abi.h | 5 ++
tools/testing/selftests/rseq/rseq.c | 68 ++++++++++++++++++++++---
tools/testing/selftests/rseq/rseq.h | 18 +++++--
3 files changed, 79 insertions(+), 12 deletions(-)
@@ -146,6 +146,11 @@ struct rseq_abi {
* this thread.
*/
__u32 flags;
+
+ /*
+ * Flexible array member at end of structure, after last feature field.
+ */
+ char end[];
} __attribute__((aligned(4 * sizeof(__u64))));
#endif /* _RSEQ_ABI_H */
@@ -28,6 +28,8 @@
#include <limits.h>
#include <dlfcn.h>
#include <stddef.h>
+#include <sys/auxv.h>
+#include <linux/auxvec.h>
#include "../kselftest.h"
#include "rseq.h"
@@ -36,20 +38,38 @@ static const ptrdiff_t *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. */
+/* Offset from the thread pointer to the rseq area. */
ptrdiff_t rseq_offset;
-/* Size of the registered rseq area. 0 if the registration was
- unsuccessful. */
+/*
+ * 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;
+/*
+ * rseq feature size supported by the kernel. 0 if the registration was
+ * unsuccessful.
+ */
+unsigned int rseq_feature_size = -1U;
+
static int rseq_ownership;
+static int rseq_reg_success; /* At least one rseq registration has succeded. */
+
+/* Allocate a large area for the TLS. */
+#define RSEQ_THREAD_AREA_ALLOC_SIZE 1024
+
+/* Original struct rseq feature size is 20 bytes. */
+#define ORIG_RSEQ_FEATURE_SIZE 20
+
+/* Orignal struct rseq allocation size is 32 bytes. */
+#define ORIG_RSEQ_ALLOC_SIZE 32
static
-__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"))) = {
+__thread struct rseq_abi __rseq_abi __attribute__((tls_model("initial-exec"), aligned(RSEQ_THREAD_AREA_ALLOC_SIZE))) = {
.cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
};
@@ -84,10 +104,18 @@ int rseq_register_current_thread(void)
/* Treat libc's ownership as a successful registration. */
return 0;
}
- rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), 0, RSEQ_SIG);
- if (rc)
+ rc = sys_rseq(&__rseq_abi, rseq_size, 0, RSEQ_SIG);
+ if (rc) {
+ if (RSEQ_READ_ONCE(rseq_reg_success)) {
+ /* Incoherent success/failure within process. */
+ abort();
+ }
+ rseq_size = 0;
+ rseq_feature_size = 0;
return -1;
+ }
assert(rseq_current_cpu_raw() >= 0);
+ RSEQ_WRITE_ONCE(rseq_reg_success, 1);
return 0;
}
@@ -99,12 +127,28 @@ int rseq_unregister_current_thread(void)
/* Treat libc's ownership as a successful unregistration. */
return 0;
}
- rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+ rc = sys_rseq(&__rseq_abi, rseq_size, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
if (rc)
return -1;
return 0;
}
+static
+unsigned int get_rseq_feature_size(void)
+{
+ unsigned long auxv_rseq_feature_size, auxv_rseq_align;
+
+ auxv_rseq_align = getauxval(AT_RSEQ_ALIGN);
+ assert(!auxv_rseq_align || auxv_rseq_align <= RSEQ_THREAD_AREA_ALLOC_SIZE);
+
+ auxv_rseq_feature_size = getauxval(AT_RSEQ_FEATURE_SIZE);
+ assert(!auxv_rseq_feature_size || auxv_rseq_feature_size <= RSEQ_THREAD_AREA_ALLOC_SIZE);
+ if (auxv_rseq_feature_size)
+ return auxv_rseq_feature_size;
+ else
+ return ORIG_RSEQ_FEATURE_SIZE;
+}
+
static __attribute__((constructor))
void rseq_init(void)
{
@@ -117,14 +161,21 @@ void rseq_init(void)
rseq_offset = *libc_rseq_offset_p;
rseq_size = *libc_rseq_size_p;
rseq_flags = *libc_rseq_flags_p;
+ rseq_feature_size = get_rseq_feature_size();
+ if (rseq_feature_size > rseq_size)
+ rseq_feature_size = rseq_size;
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;
+ rseq_feature_size = get_rseq_feature_size();
+ if (rseq_feature_size == ORIG_RSEQ_FEATURE_SIZE)
+ rseq_size = ORIG_RSEQ_ALLOC_SIZE;
+ else
+ rseq_size = RSEQ_THREAD_AREA_ALLOC_SIZE;
}
static __attribute__((destructor))
@@ -134,6 +185,7 @@ void rseq_exit(void)
return;
rseq_offset = 0;
rseq_size = -1U;
+ rseq_feature_size = -1U;
rseq_ownership = 0;
}
@@ -47,14 +47,24 @@
#include "rseq-thread-pointer.h"
-/* Offset from the thread pointer to the rseq area. */
+/* Offset from the thread pointer to the rseq area. */
extern ptrdiff_t rseq_offset;
-/* Size of the registered rseq area. 0 if the registration was
- unsuccessful. */
+
+/*
+ * Size of the registered rseq area. 0 if the registration was
+ * unsuccessful.
+ */
extern unsigned int rseq_size;
-/* Flags used during rseq registration. */
+
+/* Flags used during rseq registration. */
extern unsigned int rseq_flags;
+/*
+ * rseq feature size supported by the kernel. 0 if the registration was
+ * unsuccessful.
+ */
+extern unsigned int rseq_feature_size;
+
static inline struct rseq_abi *rseq_get_abi(void)
{
return (struct rseq_abi *) ((uintptr_t) rseq_thread_pointer() + rseq_offset);