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Commit b926e6f6 authored by Andy Lutomirski's avatar Andy Lutomirski
Browse files

x86, traps: Fix ist_enter from userspace 

context_tracking_user_exit() has no effect if in_interrupt() returns true,
so ist_enter() didn't work.  Fix it by calling exception_enter(), and thus
context_tracking_user_exit(), before incrementing the preempt count.

This also adds an assertion that will catch the problem reliably if
CONFIG_PROVE_RCU=y to help prevent the bug from being reintroduced.

Link: http://lkml.kernel.org/r/261ebee6aee55a4724746d0d7024697013c40a08.1422709102.git.luto@amacapital.net


Fixes: 95927475 x86, traps: Track entry into and exit from IST context
Reported-and-tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
parent 772a9aca

arch/x86/kernel/traps.c

+18 −7
Original line number Diff line number Diff line
@@ -110,15 +110,11 @@ static inline void preempt_conditional_cli(struct pt_regs *regs) 


enum ctx_state ist_enter(struct pt_regs *regs)

{

	/*

	 * We are atomic because we're on the IST stack (or we're on x86_32,

	 * in which case we still shouldn't schedule.

	 */

	preempt_count_add(HARDIRQ_OFFSET);

	enum ctx_state prev_state;



	if (user_mode_vm(regs)) {

		/* Other than that, we're just an exception. */

		return exception_enter();

		prev_state = exception_enter();

	} else {

		/*

		 * We might have interrupted pretty much anything.  In
@@ -127,12 +123,27 @@ enum ctx_state ist_enter(struct pt_regs *regs) 
		 * but we need to notify RCU.

		 */

		rcu_nmi_enter();

		return IN_KERNEL;  /* the value is irrelevant. */

		prev_state = IN_KERNEL;  /* the value is irrelevant. */

	}



	/*

	 * We are atomic because we're on the IST stack (or we're on x86_32,

	 * in which case we still shouldn't schedule).

	 *

	 * This must be after exception_enter(), because exception_enter()

	 * won't do anything if in_interrupt() returns true.

	 */

	preempt_count_add(HARDIRQ_OFFSET);



	/* This code is a bit fragile.  Test it. */

	rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work");



	return prev_state;

}



void ist_exit(struct pt_regs *regs, enum ctx_state prev_state)

{

	/* Must be before exception_exit. */

	preempt_count_sub(HARDIRQ_OFFSET);



	if (user_mode_vm(regs))