Introduce RSEQ_FLAG_REGISTER with the same behavior as the flag value "0". The main advantage of introducing this flag as a non-zero (1 << 1) value is that it can be combined with other flags to register and check for features with a single system call. Considering that this system call needs to be performed for each new thread in glibc, minimize the amount of overhead required.
This is needed for introducing a new RSEQ_FLAG_RELIABLE_CPU_ID flag in a later change. Signed-off-by: Mathieu Desnoyers <[email protected]> Cc: Peter Zijlstra (Intel) <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Florian Weimer <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: Boqun Feng <[email protected]> Cc: "H . Peter Anvin" <[email protected]> Cc: Paul Turner <[email protected]> Cc: Dmitry Vyukov <[email protected]> Cc: Neel Natu <[email protected]> Cc: [email protected] --- include/uapi/linux/rseq.h | 10 ++++- kernel/rseq.c | 77 +++++++++++++++++++++------------------ 2 files changed, 51 insertions(+), 36 deletions(-) diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h index 9a402fdb60e9..3b5fba25461a 100644 --- a/include/uapi/linux/rseq.h +++ b/include/uapi/linux/rseq.h @@ -18,8 +18,16 @@ enum rseq_cpu_id_state { RSEQ_CPU_ID_REGISTRATION_FAILED = -2, }; +/* + * RSEQ_FLAG_UNREGISTER: Unregister rseq ABI for caller thread. + * RSEQ_FLAG_REGISTER: Register rseq ABI for caller thread. + * + * Flag value 0 has the same behavior as RSEQ_FLAG_REGISTER, but cannot be + * combined with other flags. This behavior is kept for backward compatibility. + */ enum rseq_flags { - RSEQ_FLAG_UNREGISTER = (1 << 0), + RSEQ_FLAG_UNREGISTER = (1 << 0), + RSEQ_FLAG_REGISTER = (1 << 1), }; enum rseq_cs_flags_bit { diff --git a/kernel/rseq.c b/kernel/rseq.c index a4f86a9d6937..47ce221cd6f9 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -309,9 +309,16 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, { int ret; - if (flags & RSEQ_FLAG_UNREGISTER) { - if (flags & ~RSEQ_FLAG_UNREGISTER) - return -EINVAL; + /* + * Flag value 0 has the same behavior as RSEQ_FLAG_REGISTER, but cannot + * be combined with other flags. This behavior is kept for backward + * compatibility. + */ + if (!flags) + flags = RSEQ_FLAG_REGISTER; + + switch (flags) { + case RSEQ_FLAG_UNREGISTER: /* Unregister rseq for current thread. */ if (current->rseq != rseq || !current->rseq) return -EINVAL; @@ -324,43 +331,43 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, return ret; current->rseq = NULL; current->rseq_sig = 0; - return 0; - } - - if (unlikely(flags)) - return -EINVAL; + break; + case RSEQ_FLAG_REGISTER: + if (current->rseq) { + /* + * If rseq is already registered, check whether + * the provided address differs from the prior + * one. + */ + if (current->rseq != rseq || rseq_len != sizeof(*rseq)) + return -EINVAL; + if (current->rseq_sig != sig) + return -EPERM; + /* Already registered. */ + return -EBUSY; + } - if (current->rseq) { /* - * If rseq is already registered, check whether - * the provided address differs from the prior - * one. + * If there was no rseq previously registered, + * ensure the provided rseq is properly aligned and valid. */ - if (current->rseq != rseq || rseq_len != sizeof(*rseq)) + if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) || + rseq_len != sizeof(*rseq)) return -EINVAL; - if (current->rseq_sig != sig) - return -EPERM; - /* Already registered. */ - return -EBUSY; - } - - /* - * If there was no rseq previously registered, - * ensure the provided rseq is properly aligned and valid. - */ - if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) || - rseq_len != sizeof(*rseq)) + if (!access_ok(rseq, rseq_len)) + return -EFAULT; + current->rseq = rseq; + current->rseq_sig = sig; + /* + * If rseq was previously inactive, and has just been + * registered, ensure the cpu_id_start and cpu_id fields + * are updated before returning to user-space. + */ + rseq_set_notify_resume(current); + break; + default: return -EINVAL; - if (!access_ok(rseq, rseq_len)) - return -EFAULT; - current->rseq = rseq; - current->rseq_sig = sig; - /* - * If rseq was previously inactive, and has just been - * registered, ensure the cpu_id_start and cpu_id fields - * are updated before returning to user-space. - */ - rseq_set_notify_resume(current); + } return 0; } -- 2.17.1
