linux-kernel - Re: [patch V5 27/31] rseq: Implement fast path for exit to user

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Message-ID: <20251023085144.GW3245006@noisy.programming.kicks-ass.net>
Date: Thu, 23 Oct 2025 10:51:44 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Michael Jeanson <mjeanson@...icios.com>,
	Jens Axboe <axboe@...nel.dk>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Wei Liu <wei.liu@...nel.org>
Subject: Re: [patch V5 27/31] rseq: Implement fast path for exit to user

On Wed, Oct 22, 2025 at 02:52:34PM +0200, Thomas Gleixner wrote:
> @@ -245,12 +246,13 @@ rseq_update_user_cs(struct task_struct *
>  {
>  	struct rseq_cs __user *ucs = (struct rseq_cs __user *)(unsigned long)csaddr;
>  	unsigned long ip = instruction_pointer(regs);
> +	unsigned long tasksize = TASK_SIZE;
>  	u64 start_ip, abort_ip, offset;
>  	u32 usig, __user *uc_sig;
>  
>  	rseq_stat_inc(rseq_stats.cs);
>  
> -	if (unlikely(csaddr >= TASK_SIZE)) {
> +	if (unlikely(csaddr >= tasksize)) {
>  		t->rseq.event.fatal = true;
>  		return false;
>  	}
> @@ -287,7 +289,7 @@ rseq_update_user_cs(struct task_struct *
>  		 * in TLS::rseq::rseq_cs. An RSEQ abort would then evade ROP
>  		 * protection.
>  		 */
> -		if (abort_ip >= TASK_SIZE || abort_ip < sizeof(*uc_sig))
> +		if (unlikely(abort_ip >= tasksize || abort_ip < sizeof(*uc_sig)))
>  			goto die;
>  
>  		/* The address is guaranteed to be >= 0 and < TASK_SIZE */

This seems like a random change, unconnected to the rest of the patch.