arm64: don't call break hooks for BRK exceptions from EL0

Our break hooks are used to handle brk exceptions from kgdb (and potentially
kprobes if that code ever resurfaces), so don't bother calling them if
the BRK exception comes from userspace.

This prevents userspace from trapping to a kdb shell on systems where
kgdb is enabled and active.

Cc: <stable@vger.kernel.org>
Reported-by: Omar Sandoval <osandov@osandov.com>
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 a7fb874b595edc0c095430792de9c8883590855f..fe5b94078d82f7dc439e72aae8a369c20ef7e4e6 100644 (file)
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -315,20 +315,20 @@ static int brk_handler(unsigned long addr, unsigned int esr,
 {
        siginfo_t info;
 
-       if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
-               return 0;
+       if (user_mode(regs)) {
+               info = (siginfo_t) {
+                       .si_signo = SIGTRAP,
+                       .si_errno = 0,
+                       .si_code  = TRAP_BRKPT,
+                       .si_addr  = (void __user *)instruction_pointer(regs),
+               };
 
-       if (!user_mode(regs))
+               force_sig_info(SIGTRAP, &info, current);
+       } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
+               pr_warning("Unexpected kernel BRK exception at EL1\n");
                return -EFAULT;
+       }
 
-       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);
        return 0;
 }