ARM: 8124/1: don't enter kgdb when userspace executes a kgdb break in…

…struction

The kgdb breakpoint hooks (kgdb_brk_fn and kgdb_compiled_brk_fn)
should only be entered when a kgdb break instruction is executed
from the kernel. Otherwise, if kgdb is enabled, a userspace program
can cause the kernel to drop into the debugger by executing either
KGDB_BREAKINST or KGDB_COMPILED_BREAK.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/kgdb.c

@@ -160,12 +160,16 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr)
 static struct undef_hook kgdb_brkpt_hook = {
 	.instr_mask		= 0xffffffff,
 	.instr_val		= KGDB_BREAKINST,
+	.cpsr_mask		= MODE_MASK,
+	.cpsr_val		= SVC_MODE,
 	.fn			= kgdb_brk_fn
 };
 
 static struct undef_hook kgdb_compiled_brkpt_hook = {
 	.instr_mask		= 0xffffffff,
 	.instr_val		= KGDB_COMPILED_BREAK,
+	.cpsr_mask		= MODE_MASK,
+	.cpsr_val		= SVC_MODE,
 	.fn			= kgdb_compiled_brk_fn
 };