From 6c0aca288e726405b01dacb12cac556454d34b2a Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 11 Nov 2010 21:18:43 +0100 Subject: [PATCH] x86: Ignore trap bits on single step exceptions When a single step exception fires, the trap bits, used to signal hardware breakpoints, are in a random state. These trap bits might be set if another exception will follow, like a breakpoint in the next instruction, or a watchpoint in the previous one. Or there can be any junk there. So if we handle these trap bits during the single step exception, we are going to handle an exception twice, or we are going to handle junk. Just ignore them in this case. This fixes https://bugzilla.kernel.org/show_bug.cgi?id=21332 Reported-by: Michael Stefaniuc Signed-off-by: Frederic Weisbecker Cc: Rafael J. Wysocki Cc: Maciej Rutecki Cc: Alexandre Julliard Cc: Jason Wessel Cc: All since 2.6.33.x --- arch/x86/kernel/hw_breakpoint.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index ff15c9d..42c5942 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -433,6 +433,10 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args) dr6_p = (unsigned long *)ERR_PTR(args->err); dr6 = *dr6_p; + /* If it's a single step, TRAP bits are random */ + if (dr6 & DR_STEP) + return NOTIFY_DONE; + /* Do an early return if no trap bits are set in DR6 */ if ((dr6 & DR_TRAP_BITS) == 0) return NOTIFY_DONE; -- 2.7.4