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x86/debug: Move historical SYSENTER junk into exc_debug_kernel()

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The historical SYSENTER junk is explicitly for from-kernel, so move it
to the #DB-from-kernel handler.

It is ordered after the notifier, which is important for KGDB which uses TF
single-step and needs to consume the event before that point.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200902133201.031099736@infradead.org
This commit is contained in:
Peter Zijlstra 2020-09-02 15:25:56 +02:00 committed by Thomas Gleixner
parent 4182e94369
commit 4eb5acc391
1 changed files with 25 additions and 24 deletions
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49
arch/x86/kernel/traps.c
View file

@ -783,7 +783,7 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
*
* May run on IST stack.
*/
static void handle_debug(struct pt_regs *regs, unsigned long dr6)
static bool handle_debug(struct pt_regs *regs, unsigned long *dr6)
{
struct task_struct *tsk = current;
bool icebp;
@ -793,15 +793,13 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6)
* then it's very likely the result of an icebp/int01 trap.
* User wants a sigtrap for that.
*/
icebp = !dr6;
icebp = !*dr6;
/* Store the virtualized DR6 value */
tsk->thread.debugreg6 = dr6;
tsk->thread.debugreg6 = *dr6;
if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,
SIGTRAP) == NOTIFY_STOP) {
return;
}
if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP)
return true;
/* It's safe to allow irq's after DR6 has been saved */
cond_local_irq_enable(regs);
@ -815,25 +813,15 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6)
/*
* Reload dr6, the notifier might have changed it.
*/
dr6 = tsk->thread.debugreg6;
*dr6 = tsk->thread.debugreg6;
if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
/*
* Historical junk that used to handle SYSENTER single-stepping.
* This should be unreachable now. If we survive for a while
* without anyone hitting this warning, we'll turn this into
* an oops.
*/
tsk->thread.debugreg6 &= ~DR_STEP;
set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
regs->flags &= ~X86_EFLAGS_TF;
}
if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
send_sigtrap(regs, 0, get_si_code(dr6));
if (*dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
send_sigtrap(regs, 0, get_si_code(*dr6));
out:
cond_local_irq_disable(regs);
return false;
}
static __always_inline void exc_debug_kernel(struct pt_regs *regs,
@ -876,7 +864,20 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
if (!dr6)
goto out;
handle_debug(regs, dr6);
if (handle_debug(regs, &dr6))
goto out;
if (WARN_ON_ONCE(dr6 & DR_STEP)) {
/*
* Historical junk that used to handle SYSENTER single-stepping.
* This should be unreachable now. If we survive for a while
* without anyone hitting this warning, we'll turn this into
* an oops.
*/
dr6 &= ~DR_STEP;
set_thread_flag(TIF_SINGLESTEP);
regs->flags &= ~X86_EFLAGS_TF;
}
out:
instrumentation_end();
@ -906,7 +907,7 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
irqentry_enter_from_user_mode(regs);
instrumentation_begin();
handle_debug(regs, dr6);
handle_debug(regs, &dr6);
instrumentation_end();
irqentry_exit_to_user_mode(regs);