x86/entry: Re-order #DB handler to avoid *SAN instrumentation

vmlinux.o: warning: objtool: exc_debug()+0xbb: call to clear_ti_thread_flag.constprop.0() leaves .noinstr.text section
vmlinux.o: warning: objtool: noist_exc_debug()+0x55: call to clear_ti_thread_flag.constprop.0() leaves .noinstr.text section

Rework things so that handle_debug() looses the noinstr and move the
clear_thread_flag() into that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200603114052.127756554@infradead.org

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 5566fe50ef98fe3c5b8eb2aa4dad3ae4e366ba5b..7febae381b911adbd810678009505b0dc7d59ef3 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -775,26 +775,44 @@ static __always_inline void debug_exit(unsigned long dr7)
  *
  * May run on IST stack.
  */
-static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,
-                                bool user_icebp)
+static void handle_debug(struct pt_regs *regs, unsigned long dr6, bool user)
 {
        struct task_struct *tsk = current;
+       bool user_icebp;
        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_thread_flag(TIF_BLOCKSTEP);
+
+       /*
+        * If DR6 is zero, no point in trying to handle it. The kernel is
+        * not using INT1.
+        */
+       if (!user && !dr6)
+               return;
+
+       /*
+        * 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.
+        */
+       user_icebp = user && !dr6;
+
        /* Store the virtualized DR6 value */
        tsk->thread.debugreg6 = dr6;
 
-       instrumentation_begin();
 #ifdef CONFIG_KPROBES
        if (kprobe_debug_handler(regs)) {
-               instrumentation_end();
                return;
        }
 #endif
 
        if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, 0,
                       SIGTRAP) == NOTIFY_STOP) {
-               instrumentation_end();
                return;
        }
 
@@ -825,7 +843,6 @@ static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,
 
 out:
        cond_local_irq_disable(regs);
-       instrumentation_end();
 }
 
 static __always_inline void exc_debug_kernel(struct pt_regs *regs,
@@ -834,14 +851,6 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
        nmi_enter();
        instrumentation_begin();
        trace_hardirqs_off_finish();
-       instrumentation_end();
-
-       /*
-        * 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
@@ -850,14 +859,8 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
        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);
+       handle_debug(regs, dr6, false);
 
-       instrumentation_begin();
        if (regs->flags & X86_EFLAGS_IF)
                trace_hardirqs_on_prepare();
        instrumentation_end();
@@ -868,14 +871,10 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
                                           unsigned long dr6)
 {
        idtentry_enter_user(regs);
-       clear_thread_flag(TIF_BLOCKSTEP);
+       instrumentation_begin();
 
-       /*
-        * 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);
+       handle_debug(regs, dr6, true);
+       instrumentation_end();
        idtentry_exit_user(regs);
 }