From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE Date: Wed, 19 Feb 2020 17:04:42 +0100 Message-ID: <20200219160442.GE14946@hirez.programming.kicks-ass.net> References: <20200219144724.800607165@infradead.org> <20200219150744.604459293@infradead.org> <20200219103614.2299ff61@gandalf.local.home> <20200219154031.GE18400@hirez.programming.kicks-ass.net> <20200219155715.GD14946@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from bombadil.infradead.org ([198.137.202.133]:47622 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726645AbgBSQFC (ORCPT ); Wed, 19 Feb 2020 11:05:02 -0500 Content-Disposition: inline In-Reply-To: <20200219155715.GD14946@hirez.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org On Wed, Feb 19, 2020 at 04:57:15PM +0100, Peter Zijlstra wrote: > Something like so, I suppose... > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index 6ef00eb6fbb9..543de932dc7c 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -350,14 +350,20 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign > regs->ip == (unsigned long)native_irq_return_iret) > { > struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1; > + unsigned long *dst = &gpregs->ip; > + unsigned long *src = (void *)regs->dp; > + int i, count = 5; > > /* > * regs->sp points to the failing IRET frame on the > * ESPFIX64 stack. Copy it to the entry stack. This fills > * in gpregs->ss through gpregs->ip. > - * > */ > - memmove(&gpregs->ip, (void *)regs->sp, 5*8); > + for (i = 0; i < count; i++) { > + int idx = (dst <= src) ? i : count - i; That's an off-by-one for going backward; 'count - 1 - i' should work better, or I should just stop typing for today ;-) > + dst[idx] = src[idx]; > + } > + > gpregs->orig_ax = 0; /* Missing (lost) #GP error code */ > > /*