Subject: Re: [PATCH 2/5] entry: rseq: Call rseq_handle_notify_resume() in tracehook_notify_resume()

From: Mathieu Desnoyers <[email-masked]>
Date: Thu, 19 Aug 2021 17:41:07 -0400 (EDT)

----- On Aug 17, 2021, at 8:12 PM, Sean Christopherson [email-masked] wrote:

> Invoke rseq_handle_notify_resume() from tracehook_notify_resume() now
> that the two function are always called back-to-back by architectures
> that have rseq.  The rseq helper is stubbed out for architectures that
> don't support rseq, i.e. this is a nop across the board.
> 
> Note, tracehook_notify_resume() is horribly named and arguably does not
> belong in tracehook.h as literally every line of code in it has nothing
> to do with tracing.  But, that's been true since commit a42c6ded827d
> ("move key_repace_session_keyring() into tracehook_notify_resume()")
> first usurped tracehook_notify_resume() back in 2012.  Punt cleaning that
> mess up to future patches.
> 
> No functional change intended.

This will make it harder to introduce new code paths which consume the
NOTIFY_RESUME without calling the rseq callback, which introduces issues.
Agreed.

Acked-by: Mathieu Desnoyers <[email-masked]>

> 
> Signed-off-by: Sean Christopherson <[email-masked]>
> ---
> arch/arm/kernel/signal.c     | 1 -
> arch/arm64/kernel/signal.c   | 1 -
> arch/csky/kernel/signal.c    | 4 +---
> arch/mips/kernel/signal.c    | 4 +---
> arch/powerpc/kernel/signal.c | 4 +---
> arch/s390/kernel/signal.c    | 1 -
> include/linux/tracehook.h    | 2 ++
> kernel/entry/common.c        | 4 +---
> kernel/entry/kvm.c           | 4 +---
> 9 files changed, 7 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index a3a38d0a4c85..9df68d139965 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -670,7 +670,6 @@ do_work_pending(struct pt_regs *regs, unsigned int
> thread_flags, int syscall)
> 				uprobe_notify_resume(regs);
> 			} else {
> 				tracehook_notify_resume(regs);
> -				rseq_handle_notify_resume(NULL, regs);
> 			}
> 		}
> 		local_irq_disable();
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 23036334f4dc..22b55db13da6 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -951,7 +951,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
> 
> 			if (thread_flags & _TIF_NOTIFY_RESUME) {
> 				tracehook_notify_resume(regs);
> -				rseq_handle_notify_resume(NULL, regs);
> 
> 				/*
> 				 * If we reschedule after checking the affinity
> diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
> index 312f046d452d..bc4238b9f709 100644
> --- a/arch/csky/kernel/signal.c
> +++ b/arch/csky/kernel/signal.c
> @@ -260,8 +260,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
> 	if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> 		do_signal(regs);
> 
> -	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
> +	if (thread_info_flags & _TIF_NOTIFY_RESUME)
> 		tracehook_notify_resume(regs);
> -		rseq_handle_notify_resume(NULL, regs);
> -	}
> }
> diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
> index f1e985109da0..c9b2a75563e1 100644
> --- a/arch/mips/kernel/signal.c
> +++ b/arch/mips/kernel/signal.c
> @@ -906,10 +906,8 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, void
> *unused,
> 	if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> 		do_signal(regs);
> 
> -	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
> +	if (thread_info_flags & _TIF_NOTIFY_RESUME)
> 		tracehook_notify_resume(regs);
> -		rseq_handle_notify_resume(NULL, regs);
> -	}
> 
> 	user_enter();
> }
> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> index e600764a926c..b93b87df499d 100644
> --- a/arch/powerpc/kernel/signal.c
> +++ b/arch/powerpc/kernel/signal.c
> @@ -293,10 +293,8 @@ void do_notify_resume(struct pt_regs *regs, unsigned long
> thread_info_flags)
> 		do_signal(current);
> 	}
> 
> -	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
> +	if (thread_info_flags & _TIF_NOTIFY_RESUME)
> 		tracehook_notify_resume(regs);
> -		rseq_handle_notify_resume(NULL, regs);
> -	}
> }
> 
> static unsigned long get_tm_stackpointer(struct task_struct *tsk)
> diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
> index 78ef53b29958..b307db26bf2d 100644
> --- a/arch/s390/kernel/signal.c
> +++ b/arch/s390/kernel/signal.c
> @@ -537,5 +537,4 @@ void arch_do_signal_or_restart(struct pt_regs *regs, bool
> has_signal)
> void do_notify_resume(struct pt_regs *regs)
> {
> 	tracehook_notify_resume(regs);
> -	rseq_handle_notify_resume(NULL, regs);
> }
> diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
> index 3e80c4bc66f7..2564b7434b4d 100644
> --- a/include/linux/tracehook.h
> +++ b/include/linux/tracehook.h
> @@ -197,6 +197,8 @@ static inline void tracehook_notify_resume(struct pt_regs
> *regs)
> 
> 	mem_cgroup_handle_over_high();
> 	blkcg_maybe_throttle_current();
> +
> +	rseq_handle_notify_resume(NULL, regs);
> }
> 
> /*
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index bf16395b9e13..d5a61d565ad5 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -171,10 +171,8 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs
> *regs,
> 		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> 			handle_signal_work(regs, ti_work);
> 
> -		if (ti_work & _TIF_NOTIFY_RESUME) {
> +		if (ti_work & _TIF_NOTIFY_RESUME)
> 			tracehook_notify_resume(regs);
> -			rseq_handle_notify_resume(NULL, regs);
> -		}
> 
> 		/* Architecture specific TIF work */
> 		arch_exit_to_user_mode_work(regs, ti_work);
> diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c
> index 049fd06b4c3d..49972ee99aff 100644
> --- a/kernel/entry/kvm.c
> +++ b/kernel/entry/kvm.c
> @@ -19,10 +19,8 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu,
> unsigned long ti_work)
> 		if (ti_work & _TIF_NEED_RESCHED)
> 			schedule();
> 
> -		if (ti_work & _TIF_NOTIFY_RESUME) {
> +		if (ti_work & _TIF_NOTIFY_RESUME)
> 			tracehook_notify_resume(NULL);
> -			rseq_handle_notify_resume(NULL, NULL);
> -		}
> 
> 		ret = arch_xfer_to_guest_mode_handle_work(vcpu, ti_work);
> 		if (ret)
> --
> 2.33.0.rc1.237.g0d66db33f3-goog

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com