ptrace_write_dr7() skips ptrace_modify_breakpoint(disabled => true)
unless second_pass, this buys nothing but complicates the code and
means that we always do the main loop twice even if "disabled" was
never true.
The comment says:
Don't unregister the breakpoints right-away,
unless all register_user_hw_breakpoint()
requests have succeeded.
I think this logic was always wrong, hw_breakpoint_del() does not
free the slot so perf_event_disable() can't hurt.
But in any case this looks unneeded nowadays, and contrary to what
the comment says we do not do register_user_hw_breakpoint(), this
was removed by 24f1e32c "hw-breakpoints: Rewrite the hw-breakpoints
layer on top of perf events".
Remove the "second_pass" check from the main loop and simplify the
code. Since we have to check "bp != NULL" anyway, the patch also
removes the same check in ptrace_modify_breakpoint() and moves the
comment into ptrace_write_dr7().
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
arch/x86/kernel/ptrace.c | 46 +++++++++++++++++-----------------------------
1 files changed, 17 insertions(+), 29 deletions(-)
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 0649f16..6814f27 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -609,14 +609,6 @@ ptrace_modify_breakpoint(struct perf_event *bp, int len,
int type,
int gen_len, gen_type;
struct perf_event_attr attr;
- /*
- * We should have at least an inactive breakpoint at this
- * slot. It means the user is writing dr7 without having
- * written the address register first
- */
- if (!bp)
- return -EINVAL;
-
err = arch_bp_generic_fields(len, type, &gen_len, &gen_type);
if (err)
return err;
@@ -634,10 +626,10 @@ ptrace_modify_breakpoint(struct perf_event *bp, int len,
int type,
*/
static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data)
{
- struct thread_struct *thread = &(tsk->thread);
+ struct thread_struct *thread = &tsk->thread;
unsigned long old_dr7;
- int i, orig_ret = 0, rc = 0;
- int second_pass = 0;
+ int i, ret = 0, rc = 0;
+ bool second_pass = false;
data &= ~DR_CONTROL_RESERVED;
old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
@@ -651,35 +643,31 @@ restore:
bool disabled = !decode_dr7(data, i, &len, &type);
struct perf_event *bp = thread->ptrace_bps[i];
- if (disabled) {
+ if (!bp) {
+ if (disabled)
+ continue;
/*
- * Don't unregister the breakpoints right-away, unless
- * all register_user_hw_breakpoint() requests have
- * succeeded. This prevents any window of opportunity
- * for debug register grabbing by other users.
+ * We should have at least an inactive breakpoint at
+ * this slot. It means the user is writing dr7 without
+ * having written the address register first.
*/
- if (!bp || !second_pass)
- continue;
+ rc = -EINVAL;
+ break;
}
rc = ptrace_modify_breakpoint(bp, len, type, tsk, disabled);
if (rc)
break;
}
- /*
- * Make a second pass to free the remaining unused breakpoints
- * or to restore the original breakpoints if an error occurred.
- */
- if (!second_pass) {
- second_pass = 1;
- if (rc < 0) {
- orig_ret = rc;
- data = old_dr7;
- }
+ /* Make a second pass to restore the original breakpoints if failed */
+ if (!second_pass && rc) {
+ second_pass = true;
+ ret = rc;
+ data = old_dr7;
goto restore;
}
- return orig_ret < 0 ? orig_ret : rc;
+ return ret;
}
/*
--
1.5.5.1
--
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