linux-kernel - [patch V4 part 3 01/29] x86/traps: Mark fixup_bad

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Date:   Tue, 05 May 2020 15:43:55 +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>
Subject: [patch V4 part 3 01/29] x86/traps: Mark fixup_bad_iret() noinstr

This is called from deep entry ASM in a situation where instrumentation
will cause more harm than providing useful information.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/traps.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -621,7 +621,7 @@ struct bad_iret_stack {
 	struct pt_regs regs;
 };
 
-asmlinkage __visible notrace
+asmlinkage __visible noinstr
 struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 {
 	/*
@@ -632,19 +632,21 @@ struct bad_iret_stack *fixup_bad_iret(st
 	 * just below the IRET frame) and we want to pretend that the
 	 * exception came from the IRET target.
 	 */
-	struct bad_iret_stack *new_stack =
-		(struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+	struct bad_iret_stack tmp, *new_stack =
+		(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 
-	/* Copy the IRET target to the new stack. */
-	memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
+	/* Copy the IRET target to the temporary storage. */
+	memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
 
 	/* Copy the remainder of the stack from the current stack. */
-	memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
+	memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+
+	/* Update the entry stack */
+	memcpy(new_stack, &tmp, sizeof(tmp));
 
 	BUG_ON(!user_mode(&new_stack->regs));
 	return new_stack;
 }
-NOKPROBE_SYMBOL(fixup_bad_iret);
 #endif
 
 static bool is_sysenter_singlestep(struct pt_regs *regs)