x86, traps: converge do_debug handlers

Make the x86_64-version and the i386-version of do_debug
more similar.

 - introduce preempt_conditional_sti/cli to i386. The preempt-count
	is now elevated during the trap handler, like on x86_64. It
	does not run on a separate stack, however.
 - replace an open-coded "send_sigtrap"
 - copy some comments

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 30 insertions, 17 deletions

diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index 7eb1203c909d..953172af6e51 100644
--- a/arch/x86/kernel/traps_32.c
+++ b/arch/x86/kernel/traps_32.c
@@ -88,6 +88,20 @@ static inline void conditional_sti(struct pt_regs *regs)
                 local_irq_enable();
 }
 
+static inline void preempt_conditional_sti(struct pt_regs *regs)
+{
+        inc_preempt_count();
+        if (regs->flags & X86_EFLAGS_IF)
+                local_irq_enable();
+}
+
+static inline void preempt_conditional_cli(struct pt_regs *regs)
+{
+        if (regs->flags & X86_EFLAGS_IF)
+                local_irq_disable();
+        dec_preempt_count();
+}
+
 static inline void
 die_if_kernel(const char *str, struct pt_regs *regs, long err)
 {
@@ -498,7 +512,7 @@ dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
 dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 {
         struct task_struct *tsk = current;
-        unsigned int condition;
+        unsigned long condition;
         int si_code;
 
         get_debugreg(condition, 6);
@@ -512,9 +526,9 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
         if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
                                                 SIGTRAP) == NOTIFY_STOP)
                 return;
+
         /* It's safe to allow irq's after DR6 has been saved */
-        if (regs->flags & X86_EFLAGS_IF)
-                local_irq_enable();
+        preempt_conditional_sti(regs);
 
         /* Mask out spurious debug traps due to lazy DR7 setting */
         if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
@@ -533,16 +547,11 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
          * kernel space (but re-enable TF when returning to user mode).
          */
         if (condition & DR_STEP) {
-                /*
-                 * We already checked v86 mode above, so we can
-                 * check for kernel mode by just checking the CPL
-                 * of CS.
-                 */
                 if (!user_mode(regs))
                         goto clear_TF_reenable;
         }
 
-        si_code = get_si_code((unsigned long)condition);
+        si_code = get_si_code(condition);
         /* Ok, finally something we can handle */
         send_sigtrap(tsk, regs, error_code, si_code);
 
@@ -552,15 +561,18 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
          */
 clear_dr7:
         set_debugreg(0, 7);
+        preempt_conditional_cli(regs);
         return;
 
 debug_vm86:
         handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
+        preempt_conditional_cli(regs);
         return;
 
 clear_TF_reenable:
         set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
         regs->flags &= ~X86_EFLAGS_TF;
+        preempt_conditional_cli(regs);
         return;
 }
 
diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index be73323ca952..a851eca6d04c 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -380,7 +380,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 {
         struct task_struct *tsk = current;
         unsigned long condition;
-        siginfo_t info;
+        int si_code;
 
         get_debugreg(condition, 6);
 
@@ -394,6 +394,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                                                 SIGTRAP) == NOTIFY_STOP)
                 return;
 
+        /* It's safe to allow irq's after DR6 has been saved */
         preempt_conditional_sti(regs);
 
         /* Mask out spurious debug traps due to lazy DR7 setting */
@@ -402,6 +403,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                         goto clear_dr7;
         }
 
+        /* Save debug status register where ptrace can see it */
         tsk->thread.debugreg6 = condition;
 
         /*
@@ -413,15 +415,14 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                         goto clear_TF_reenable;
         }
 
+        si_code = get_si_code(condition);
         /* Ok, finally something we can handle */
-        tsk->thread.trap_no = 1;
-        tsk->thread.error_code = error_code;
-        info.si_signo = SIGTRAP;
-        info.si_errno = 0;
-        info.si_code = get_si_code(condition);
-        info.si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
-        force_sig_info(SIGTRAP, &info, tsk);
+        send_sigtrap(tsk, regs, error_code, si_code);
 
+        /*
+         * Disable additional traps. They'll be re-enabled when
+         * the signal is delivered.
+         */
 clear_dr7:
         set_debugreg(0, 7);
         preempt_conditional_cli(regs);