Re: [PATCH 7/8] powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess switches

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: "Christopher M. Riedl" <cmr@codefail.de>, linuxppc-dev@lists.ozlabs.org
Cc: Daniel Axtens <dja@axtens.net>
Subject: Re: [PATCH 7/8] powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess switches
Date: Fri, 16 Oct 2020 16:00:20 +0200	[thread overview]
Message-ID: <1cedcf43-4594-5db1-d248-7c06a572aecc@csgroup.eu> (raw)
In-Reply-To: <20201015150159.28933-8-cmr@codefail.de>

Le 15/10/2020 à 17:01, Christopher M. Riedl a écrit :
> From: Daniel Axtens <dja@axtens.net>
> 
> Add uaccess blocks and use the 'unsafe' versions of functions doing user
> access where possible to reduce the number of times uaccess has to be
> opened/closed.
> 
> There is no 'unsafe' version of copy_siginfo_to_user, so move it
> slightly to allow for a "longer" uaccess block.
> 
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> ---
>   arch/powerpc/kernel/signal_64.c | 54 ++++++++++++++++-----------------
>   1 file changed, 27 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
> index 6d4f7a5c4fbf..3b97e3681a8f 100644
> --- a/arch/powerpc/kernel/signal_64.c
> +++ b/arch/powerpc/kernel/signal_64.c
> @@ -843,46 +843,42 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
>   	/* Save the thread's msr before get_tm_stackpointer() changes it */
>   	unsigned long msr = regs->msr;
>   #endif
> -
>   	frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
> -	if (!access_ok(frame, sizeof(*frame)))
> +	if (!user_write_access_begin(frame, sizeof(*frame)))
>   		goto badframe;
>   
> -	err |= __put_user(&frame->info, &frame->pinfo);
> -	err |= __put_user(&frame->uc, &frame->puc);
> -	err |= copy_siginfo_to_user(&frame->info, &ksig->info);
> -	if (err)
> -		goto badframe;
> +	unsafe_put_user(&frame->info, &frame->pinfo, badframe_block);
> +	unsafe_put_user(&frame->uc, &frame->puc, badframe_block);
>   
>   	/* Create the ucontext.  */
> -	err |= __put_user(0, &frame->uc.uc_flags);
> -	err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
> +	unsafe_put_user(0, &frame->uc.uc_flags, badframe_block);
> +	unsafe_save_altstack(&frame->uc.uc_stack, regs->gpr[1], badframe_block);
> +
>   #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>   	if (MSR_TM_ACTIVE(msr)) {
>   		/* The ucontext_t passed to userland points to the second
>   		 * ucontext_t (for transactional state) with its uc_link ptr.
>   		 */
> -		err |= __put_user(&frame->uc_transact, &frame->uc.uc_link);
> +		unsafe_put_user(&frame->uc_transact, &frame->uc.uc_link, badframe_block);
> +		user_write_access_end();

Whaou. Doing this inside an #ifdef sequence is dirty.
Can you reorganise code to avoid that and to avoid nesting #ifdef/#endif and the if/else as I did in 
signal32 ?

>   		err |= setup_tm_sigcontexts(&frame->uc.uc_mcontext,
>   					    &frame->uc_transact.uc_mcontext,
>   					    tsk, ksig->sig, NULL,
>   					    (unsigned long)ksig->ka.sa.sa_handler,
>   					    msr);
> +		if (!user_write_access_begin(frame, sizeof(struct rt_sigframe)))
> +			goto badframe;
> +
>   	} else
>   #endif
>   	{
> -		err |= __put_user(0, &frame->uc.uc_link);
> -
> -		if (!user_write_access_begin(frame, sizeof(struct rt_sigframe)))
> -			return -EFAULT;
> -		err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
> -						ksig->sig, NULL,
> -						(unsigned long)ksig->ka.sa.sa_handler, 1);
> -		user_write_access_end();
> +		unsafe_put_user(0, &frame->uc.uc_link, badframe_block);
> +		unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
> +					NULL, (unsigned long)ksig->ka.sa.sa_handler,
> +					1, badframe_block);
>   	}
> -	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
> -	if (err)
> -		goto badframe;
> +
> +	unsafe_copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set), badframe_block);
>   
>   	/* Make sure signal handler doesn't get spurious FP exceptions */
>   	tsk->thread.fp_state.fpscr = 0;
> @@ -891,15 +887,17 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
>   	if (vdso64_rt_sigtramp && tsk->mm->context.vdso_base) {
>   		regs->nip = tsk->mm->context.vdso_base + vdso64_rt_sigtramp;
>   	} else {
> -		if (!user_write_access_begin(frame, sizeof(struct rt_sigframe)))
> -			return -EFAULT;
> -		err |= __unsafe_setup_trampoline(__NR_rt_sigreturn, &frame->tramp[0]);
> -		user_write_access_end();
> -		if (err)
> -			goto badframe;
> +		unsafe_setup_trampoline(__NR_rt_sigreturn, &frame->tramp[0],
> +					badframe_block);
>   		regs->nip = (unsigned long) &frame->tramp[0];
>   	}
>   
> +	user_write_access_end();
> +
> +	/* Save the siginfo outside of the unsafe block. */
> +	if (copy_siginfo_to_user(&frame->info, &ksig->info))
> +		goto badframe;
> +
>   	/* Allocate a dummy caller frame for the signal handler. */
>   	newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;
>   	err |= put_user(regs->gpr[1], (unsigned long __user *)newsp);
> @@ -939,6 +937,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
>   
>   	return 0;
>   
> +badframe_block:
> +	user_write_access_end();
>   badframe:
>   	signal_fault(current, regs, "handle_rt_signal64", frame);
>   
> 

Christophe