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Date:   Tue, 05 May 2020 15:16:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch V4 part 1 08/36] x86/doublefault: Remove memmove() call

Use of memmove() in #DF is problematic considered tracing and other
instrumentation.

Remove the memmove() call and simply write out what needs doing; this
even clarifies the code, win-win! The code copies from the espfix64
stack to the normal task stack, there is no possible way for that to
overlap.

Survives selftests/x86, specifically sigreturn_64.

Suggested-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Andy Lutomirski <luto@...nel.org>
Link: https://lkml.kernel.org/r/20200220121727.GB507@zn.tnic
---
 arch/x86/kernel/traps.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -278,6 +278,7 @@ dotraplinkage void do_double_fault(struc
 		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 *p = (unsigned long *)regs->sp;
 
 		/*
 		 * regs->sp points to the failing IRET frame on the
@@ -285,7 +286,11 @@ dotraplinkage void do_double_fault(struc
 		 * in gpregs->ss through gpregs->ip.
 		 *
 		 */
-		memmove(&gpregs->ip, (void *)regs->sp, 5*8);
+		gpregs->ip	= p[0];
+		gpregs->cs	= p[1];
+		gpregs->flags	= p[2];
+		gpregs->sp	= p[3];
+		gpregs->ss	= p[4];
 		gpregs->orig_ax = 0;  /* Missing (lost) #GP error code */
 
 		/*

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