arm64: debug: re-enable irqs before sending breakpoint SIGTRAP

force_sig_info can sleep under an -rt kernel, so attempting to send a
breakpoint SIGTRAP with interrupts disabled yields the following BUG:

  BUG: sleeping function called from invalid context at
  /kernel-source/kernel/locking/rtmutex.c:917
  in_atomic(): 0, irqs_disabled(): 128, pid: 551, name: test.sh
  CPU: 5 PID: 551 Comm: test.sh Not tainted 4.1.13-rt13 #7
  Hardware name: Freescale Layerscape 2085a RDB Board (DT)
  Call trace:
	 dump_backtrace+0x0/0x128
	 show_stack+0x24/0x30
	 dump_stack+0x80/0xa0
	 ___might_sleep+0x128/0x1a0
	 rt_spin_lock+0x2c/0x40
	 force_sig_info+0xcc/0x210
	 brk_handler.part.2+0x6c/0x80
	 brk_handler+0xd8/0xe8
	 do_debug_exception+0x58/0xb8

This patch fixes the problem by ensuring that interrupts are enabled
prior to sending the SIGTRAP if they were already enabled in the user
context.

Reported-by: Yang Shi <yang.shi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 8aee3ae..c536c9e 100644 (file)
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -226,11 +226,28 @@ static int call_step_hook(struct pt_regs *regs, unsigned int esr)
        return retval;
 }
 
+static void send_user_sigtrap(int si_code)
+{
+       struct pt_regs *regs = current_pt_regs();
+       siginfo_t info = {
+               .si_signo       = SIGTRAP,
+               .si_errno       = 0,
+               .si_code        = si_code,
+               .si_addr        = (void __user *)instruction_pointer(regs),
+       };
+
+       if (WARN_ON(!user_mode(regs)))
+               return;
+
+       if (interrupts_enabled(regs))
+               local_irq_enable();
+
+       force_sig_info(SIGTRAP, &info, current);
+}
+
 static int single_step_handler(unsigned long addr, unsigned int esr,
                               struct pt_regs *regs)
 {
-       siginfo_t info;
-
        /*
         * If we are stepping a pending breakpoint, call the hw_breakpoint
         * handler first.
@@ -239,11 +256,7 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
                return 0;
 
        if (user_mode(regs)) {
-               info.si_signo = SIGTRAP;
-               info.si_errno = 0;
-               info.si_code  = TRAP_HWBKPT;
-               info.si_addr  = (void __user *)instruction_pointer(regs);
-               force_sig_info(SIGTRAP, &info, current);
+               send_user_sigtrap(TRAP_HWBKPT);
 
                /*
                 * ptrace will disable single step unless explicitly
@@ -307,17 +320,8 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 static int brk_handler(unsigned long addr, unsigned int esr,
                       struct pt_regs *regs)
 {
-       siginfo_t info;
-
        if (user_mode(regs)) {
-               info = (siginfo_t) {
-                       .si_signo = SIGTRAP,
-                       .si_errno = 0,
-                       .si_code  = TRAP_BRKPT,
-                       .si_addr  = (void __user *)instruction_pointer(regs),
-               };
-
-               force_sig_info(SIGTRAP, &info, current);
+               send_user_sigtrap(TRAP_BRKPT);
        } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
                pr_warning("Unexpected kernel BRK exception at EL1\n");
                return -EFAULT;
@@ -328,7 +332,6 @@ static int brk_handler(unsigned long addr, unsigned int esr,
 
 int aarch32_break_handler(struct pt_regs *regs)
 {
-       siginfo_t info;
        u32 arm_instr;
        u16 thumb_instr;
        bool bp = false;
@@ -359,14 +362,7 @@ int aarch32_break_handler(struct pt_regs *regs)
        if (!bp)
                return -EFAULT;
 
-       info = (siginfo_t) {
-               .si_signo = SIGTRAP,
-               .si_errno = 0,
-               .si_code  = TRAP_BRKPT,
-               .si_addr  = pc,
-       };
-
-       force_sig_info(SIGTRAP, &info, current);
+       send_user_sigtrap(TRAP_BRKPT);
        return 0;
 }