Ravi Bangoria wrote:
If watchpoint exception is generated by larx/stcx instructions, the
reservation created by larx gets lost while handling exception, and
thus stcx instruction always fails. Generally these instructions are
used in a while(1) loop, for example spinlocks. And because stcx
never succeeds, it loops forever and ultimately hangs the system.
Note that ptrace anyway works in one-shot mode and thus for ptrace
we don't change the behaviour. It's up to ptrace user to take care
of this.
Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com>
---
arch/powerpc/kernel/hw_breakpoint.c | 49 +++++++++++++++++++----------
1 file changed, 33 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/kernel/hw_breakpoint.c
b/arch/powerpc/kernel/hw_breakpoint.c
index 28ad3171bb82..9fa496a598ce 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -195,14 +195,32 @@ void thread_change_pc(struct task_struct *tsk, struct
pt_regs *regs)
tsk->thread.last_hit_ubp = NULL;
}
+static bool is_larx_stcx_instr(struct pt_regs *regs, unsigned int instr)
+{
+ int ret, type;
+ struct instruction_op op;
+
+ ret = analyse_instr(&op, regs, instr);
+ type = GETTYPE(op.type);
+ return (!ret && (type == LARX || type == STCX));
+}
+
/*
* Handle debug exception notifications.
*/
static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
unsigned long addr)
{
- int stepped;
- unsigned int instr;
+ unsigned int instr = 0;
+
+ if (__get_user_inatomic(instr, (unsigned int *)regs->nip))
+ goto fail;
+
+ if (is_larx_stcx_instr(regs, instr)) {
+ printk_ratelimited("Watchpoint: Can't emulate/single-step larx/"
+ "stcx instructions. Disabling
watchpoint.\n");
The below WARN() uses the term 'breakpoint'. Better to use consistent
terminology. I would rewrite the above as:
printk_ratelimited("Breakpoint hit on instruction that can't be emulated.
"
"Breakpoint at 0x%lx will be disabled.\n",
addr);
Otherwise:
Acked-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
- Naveen
+ goto disable;
+ }
/* Do not emulate user-space instructions, instead single-step them */
if (user_mode(regs)) {
@@ -211,23 +229,22 @@ static bool stepping_handler(struct pt_regs *regs, struct
perf_event *bp,
return false;
}
- stepped = 0;
- instr = 0;
- if (!__get_user_inatomic(instr, (unsigned int *)regs->nip))
- stepped = emulate_step(regs, instr);
+ if (!emulate_step(regs, instr))
+ goto fail;
+ return true;
+
+fail:
/*
- * emulate_step() could not execute it. We've failed in reliably
- * handling the hw-breakpoint. Unregister it and throw a warning
- * message to let the user know about it.
+ * We've failed in reliably handling the hw-breakpoint. Unregister
+ * it and throw a warning message to let the user know about it.
*/
- if (!stepped) {
- WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
- "0x%lx will be disabled.", addr);
- perf_event_disable_inatomic(bp);
- return false;
- }
- return true;
+ WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
+ "0x%lx will be disabled.", addr);
+
+disable:
+ perf_event_disable_inatomic(bp);
+ return false;
}
int hw_breakpoint_handler(struct die_args *args)
--
2.21.0
