diff mbox series

nptl: initialize rseq area prior to registration

Message ID 20241015183844.1200634-1-mjeanson@efficios.com
State New
Headers show
Series nptl: initialize rseq area prior to registration | expand

Commit Message

Michael Jeanson Oct. 15, 2024, 6:38 p.m. UTC 
Per the rseq syscall documentation, 3 fields are required to be
initialized by userspace prior to registration, they are 'cpu_id',
'rseq_cs' and 'flags'. Since we have no guarantee that 'struct pthread'
is cleared on all architectures, explicitly set those 3 fields prior to
registration.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
---
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 nptl/descr.h                            |  2 ++
 sysdeps/unix/sysv/linux/rseq-internal.h | 10 ++++++++++
 2 files changed, 12 insertions(+)
diff mbox series

Patch

diff --git a/nptl/descr.h b/nptl/descr.h
index 65d3baaee3..66e4be1fa7 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -414,6 +414,8 @@  struct pthread
     {
       uint32_t cpu_id_start;
       uint32_t cpu_id;
+      uint64_t rseq_cs;
+      uint32_t flags;
     };
     char pad[32];		/* Original rseq area size.  */
   } rseq_area __attribute__ ((aligned (32)));
diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
index 7ea935b4ad..37a8f630b6 100644
--- a/sysdeps/unix/sysv/linux/rseq-internal.h
+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
@@ -51,11 +51,21 @@  rseq_register_current_thread (struct pthread *self, bool do_rseq)
         /* The initial implementation used only 20 bytes out of 32,
            but still expected size 32.  */
         size = RSEQ_AREA_SIZE_INITIAL;
+
+      /* Initialize the rseq fields that are read by the kernel on
+         registration, there is no guarantee that struct pthread is
+         cleared on all architectures.  */
+      THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_UNINITIALIZED);
+      THREAD_SETMEM (self, rseq_area.rseq_cs, 0);
+      THREAD_SETMEM (self, rseq_area.flags, 0);
+
       int ret = INTERNAL_SYSCALL_CALL (rseq, &self->rseq_area,
                                        size, 0, RSEQ_SIG);
       if (!INTERNAL_SYSCALL_ERROR_P (ret))
         return true;
     }
+  /* When rseq is disabled by tunables or the registration fails, inform
+     userspace by setting 'cpu_id' to RSEQ_CPU_ID_REGISTRATION_FAILED.  */
   THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
   return false;
 }