commit 97f60abd25628425971f07e9b0e7f8eec0741235 Author: Michael Jeanson Date: Thu Nov 7 22:23:49 2024 +0100 nptl: initialize rseq area prior to registration 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 Reviewed-by: Florian Weimer diff --git a/nptl/descr.h b/nptl/descr.h index 6484e3703f9a0a97..c08c5149c7239e7c 100644 --- a/nptl/descr.h +++ b/nptl/descr.h @@ -424,6 +424,8 @@ 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 ccb16640133fa9e3..7e70ae7ebdee4917 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; }