The patch titled
Subject: ptrace/x86: dont delay "disable" till second pass in ptrace_write_dr7()
has been added to the -mm tree. Its filename is
ptrace-x86-dont-delay-disable-till-second-pass-in-ptrace_write_dr7.patch
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From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: ptrace/x86: dont delay "disable" till second pass in ptrace_write_dr7()
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.
Firstly, we do not do register_user_hw_breakpoint(), it was removed by
24f1e32c ("hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf
events").
We are going to restore register_user_hw_breakpoint() (see the next patch)
but this doesn't matter, after 44234adc "hw-breakpoints: Modify
breakpoints without unregistering them" perf_event_disable() can not hurt,
hw_breakpoint_del() does not free the slot.
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().
With this patch the second pass is only needed to restore the saved
old_dr7. This should never fail, so the patch adds WARN_ON() to catch the
potential problems as Frederic suggested.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jan Kratochvil <jan.kratochvil@xxxxxxxxxx>
Cc: Michael Neuling <mikey@xxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Prasad <prasad@xxxxxxxxxxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/ptrace.c | 53 +++++++++++++------------------------
1 file changed, 20 insertions(+), 33 deletions(-)
diff -puN arch/x86/kernel/ptrace.c~ptrace-x86-dont-delay-disable-till-second-pass-in-ptrace_write_dr7 arch/x86/kernel/ptrace.c
--- a/arch/x86/kernel/ptrace.c~ptrace-x86-dont-delay-disable-till-second-pass-in-ptrace_write_dr7
+++ a/arch/x86/kernel/ptrace.c
@@ -609,14 +609,6 @@ ptrace_modify_breakpoint(struct perf_eve
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;
@@ -634,52 +626,47 @@ ptrace_modify_breakpoint(struct perf_eve
*/
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;
+ bool second_pass = false;
+ int i, rc, ret = 0;
data &= ~DR_CONTROL_RESERVED;
old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
+
restore:
- /*
- * Loop through all the hardware breakpoints, making the
- * appropriate changes to each.
- */
+ rc = 0;
for (i = 0; i < HBP_NUM; i++) {
unsigned len, type;
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;
- }
+
+ /* Restore if the first pass failed, second_pass shouldn't fail. */
+ if (rc && !WARN_ON(second_pass)) {
+ ret = rc;
+ data = old_dr7;
+ second_pass = true;
goto restore;
}
- return orig_ret < 0 ? orig_ret : rc;
+ return ret;
}
/*
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
posix_cpu_timer-consolidate-expiry-time-type.patch
posix_cpu_timers-consolidate-timer-list-cleanups.patch
posix_cpu_timers-consolidate-expired-timers-check.patch
posix-timers-correctly-get-dying-task-time-sample-in-posix_cpu_timer_schedule.patch
posix_timers-fix-racy-timer-delta-caching-on-task-exit.patch
lockdep-introduce-lock_acquire_exclusive-shared-helper-macros.patch
lglock-update-lockdep-annotations-to-report-recursive-local-locks.patch
autofs4-allow-autofs-to-work-outside-the-initial-pid-namespace.patch
autofs4-translate-pids-to-the-right-namespace-for-the-daemon.patch
ptrace-x86-revert-hw_breakpoints-fix-racy-access-to-ptrace-breakpoints.patch
ptrace-powerpc-revert-hw_breakpoints-fix-racy-access-to-ptrace-breakpoints.patch
ptrace-arm-revert-hw_breakpoints-fix-racy-access-to-ptrace-breakpoints.patch
ptrace-sh-revert-hw_breakpoints-fix-racy-access-to-ptrace-breakpoints.patch
ptrace-revert-prepare-to-fix-racy-accesses-on-task-breakpoints.patch
ptrace-x86-simplify-the-disable-logic-in-ptrace_write_dr7.patch
ptrace-x86-dont-delay-disable-till-second-pass-in-ptrace_write_dr7.patch
ptrace-x86-introduce-ptrace_register_breakpoint.patch
ptrace-x86-ptrace_write_dr7-should-create-bp-if-disabled.patch
ptrace-x86-cleanup-ptrace_set_debugreg.patch
ptrace-ptrace_detach-should-do-flush_ptrace_hw_breakpointchild.patch
ptrace-x86-flush_ptrace_hw_breakpoint-shoule-clear-the-virtual-debug-registers.patch
x86-kill-tif_debug.patch
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