[PATCH 09/11] ARM: traps: Move the BUG handling from die() to do_undefinstr()

[Sebastian Andrzej Siewior <sebastian@breakpoint.cc>]

The BUG() macro uses an opcode which is treated as an invalid opcode by
the ARM core. There is no dedicated handling for this. Instead, should
the core step onto an invalid opcode then the do_undefinstr() will
eventually end in die(). At this point, the kernel will crash and stop
invoking opcodes.

Move the BUG handling earlier to do_undefinstr() in the kernel block.
This allows a different handling if a BUG-entry is found.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
---
 arch/arm/kernel/traps.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index afbd2ebe5c39d..1353bf24da53f 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -355,14 +355,10 @@ static void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
  */
 void die(const char *str, struct pt_regs *regs, int err)
 {
-	enum bug_trap_type bug_type = BUG_TRAP_TYPE_NONE;
-	unsigned long flags = oops_begin();
+	unsigned long flags;
 	int sig = SIGSEGV;
 
-	if (!user_mode(regs))
-		bug_type = report_bug(regs->ARM_pc, regs);
-	if (bug_type != BUG_TRAP_TYPE_NONE)
-		str = "Oops - BUG";
+	flags = oops_begin();
 
 	if (__die(str, err, regs))
 		sig = 0;
@@ -442,6 +438,26 @@ int call_undef_hook(struct pt_regs *regs, unsigned int instr)
 	return fn ? fn(regs, instr) : 1;
 }
 
+static int handle_bug_opcode(unsigned int instr, struct pt_regs *regs)
+{
+	enum bug_trap_type bug_type;
+	unsigned long flags;
+	int sig = SIGSEGV;
+
+	if (instr != BUG_INSTR_VALUE)
+		return 0;
+
+	bug_type = report_bug(regs->ARM_pc, regs);
+	if (bug_type == BUG_TRAP_TYPE_NONE)
+		return 0;
+
+	flags = oops_begin();
+	if (__die("Oops - BUG", 0, regs))
+		sig = 0;
+	oops_end(flags, regs, sig);
+	return 1;
+}
+
 asmlinkage void do_undefinstr(struct pt_regs *regs)
 {
 	unsigned int instr;
@@ -461,6 +477,10 @@ asmlinkage void do_undefinstr(struct pt_regs *regs)
 		} else
 #endif
 			instr = __mem_to_opcode_arm(*(u32 *) pc);
+
+		if (handle_bug_opcode(instr, regs))
+			return;
+
 	} else if (thumb_mode(regs)) {
 		if (get_user(instr, (u16 __user *)pc))
 			goto die_sig;

-- 
2.55.0