If a watchpoint is hit when in kernel mode it is possible for the system
to end up in an infinite loop processing the watchpoint. This can happen
if a user sets a watchpoint in the kernel addess space (which is
possible in certain EVA configurations) or if a user sets a watchpoint
in a user area accessed directly by the kernel (eg. a user buffer
accessed via a syscall).
To prevent the infinite loop ensure that the watchpoint was hit in
userspace, and clear the watchpoint registers otherwise.
As this change could mean that a watchpoint is not hit when it should be
(when returning to the interrupted traced task on exception exit), the
resume_userspace path needs to be extended to conditionally restore the
watchpoint configuration. If a task switch occurs when returning to
userspace, the watchpoints will be restored in a typical way in the
switch_to() handler.
Signed-off-by: Marcin Nowakowski <marcin.nowakowski@xxxxxxxxxx>
---
arch/mips/kernel/entry.S | 9 ++++++++-
arch/mips/kernel/traps.c | 2 +-
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
index 7791840..1982fc6 100644
--- a/arch/mips/kernel/entry.S
+++ b/arch/mips/kernel/entry.S
@@ -55,7 +55,14 @@ resume_userspace:
LONG_L a2, TI_FLAGS($28) # current->work
andi t0, a2, _TIF_WORK_MASK # (ignoring syscall_trace)
bnez t0, work_pending
- j restore_all
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+ li t0, _TIF_LOAD_WATCH
+ and t0, a2, t0
+ beqz t0, 1f
+ PTR_L a0, TI_TASK($28)
+ jal mips_install_watch_registers
+#endif
+1: j restore_all
#ifdef CONFIG_PREEMPT
resume_kernel:
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 6c7f9d7..5371cb0 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -1525,7 +1525,7 @@ asmlinkage void do_watch(struct pt_regs *regs)
* their values and send SIGTRAP. Otherwise another thread
* left the registers set, clear them and continue.
*/
- if (test_tsk_thread_flag(current, TIF_LOAD_WATCH)) {
+ if (user_mode(regs) && test_tsk_thread_flag(current, TIF_LOAD_WATCH)) {
mips_read_watch_registers();
local_irq_enable();
force_sig_info(SIGTRAP, &info, current);
--
2.7.4
