x86/traps: Restructure #DB handling

Now that there are separate entry points, move the kernel/user_mode specifc
checks into the entry functions so the common handling code does not need
the extra mode checks. Make the code more readable while at it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505135315.283276272@linutronix.de

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4f248c5..b62e962 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -775,39 +775,12 @@ static __always_inline void debug_exit(unsigned long dr7)
  *
  * May run on IST stack.
  */
-static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6)
+static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,
+                                bool user_icebp)
 {
        struct task_struct *tsk = current;
-       int user_icebp = 0;
        int si_code;
 
-       /*
-        * The SDM says "The processor clears the BTF flag when it
-        * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
-        * TIF_BLOCKSTEP in sync with the hardware BTF flag.
-        */
-       clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
-
-       if (unlikely(!user_mode(regs) && (dr6 & DR_STEP) &&
-                    is_sysenter_singlestep(regs))) {
-               dr6 &= ~DR_STEP;
-               if (!dr6)
-                       return;
-               /*
-                * else we might have gotten a single-step trap and hit a
-                * watchpoint at the same time, in which case we should fall
-                * through and handle the watchpoint.
-                */
-       }
-
-       /*
-        * If dr6 has no reason to give us about the origin of this trap,
-        * then it's very likely the result of an icebp/int01 trap.
-        * User wants a sigtrap for that.
-        */
-       if (!dr6 && user_mode(regs))
-               user_icebp = 1;
-
        /* Store the virtualized DR6 value */
        tsk->thread.debugreg6 = dr6;
 
@@ -832,9 +805,7 @@ static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6)
        if (v8086_mode(regs)) {
                handle_vm86_trap((struct kernel_vm86_regs *) regs, 0,
                                 X86_TRAP_DB);
-               cond_local_irq_disable(regs);
-               debug_stack_usage_dec();
-               return;
+               goto out;
        }
 
        if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
@@ -848,9 +819,12 @@ static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6)
                set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
                regs->flags &= ~X86_EFLAGS_TF;
        }
+
        si_code = get_si_code(tsk->thread.debugreg6);
        if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
                send_sigtrap(regs, 0, si_code);
+
+out:
        cond_local_irq_disable(regs);
        debug_stack_usage_dec();
 }
@@ -859,7 +833,27 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
                                             unsigned long dr6)
 {
        nmi_enter();
-       handle_debug(regs, dr6);
+       /*
+        * The SDM says "The processor clears the BTF flag when it
+        * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
+        * TIF_BLOCKSTEP in sync with the hardware BTF flag.
+        */
+       clear_thread_flag(TIF_BLOCKSTEP);
+
+       /*
+        * Catch SYSENTER with TF set and clear DR_STEP. If this hit a
+        * watchpoint at the same time then that will still be handled.
+        */
+       if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))
+               dr6 &= ~DR_STEP;
+
+       /*
+        * If DR6 is zero, no point in trying to handle it. The kernel is
+        * not using INT1.
+        */
+       if (dr6)
+               handle_debug(regs, dr6, false);
+
        nmi_exit();
 }
 
@@ -867,7 +861,14 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
                                           unsigned long dr6)
 {
        idtentry_enter(regs);
-       handle_debug(regs, dr6);
+       clear_thread_flag(TIF_BLOCKSTEP);
+
+       /*
+        * If dr6 has no reason to give us about the origin of this trap,
+        * then it's very likely the result of an icebp/int01 trap.
+        * User wants a sigtrap for that.
+        */
+       handle_debug(regs, dr6, !dr6);
        idtentry_exit(regs);
 }