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ptrace/x86: dont delay "disable" till second pass in ptrace_write_dr7()

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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
commit 24f1e32c60 ("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 commit 44234adcdc
("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@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2013-07-08 16:00:58 -07:00 committed by Linus Torvalds
parent e6a7d60771
commit 29a5551341
1 changed files with 21 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
arch/x86/kernel/ptrace.c
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@ -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;
@ -634,52 +626,47 @@ 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;
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) {
/*
* 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.
*/
if (!bp || !second_pass)
if (!bp) {
if (disabled)
continue;
/*
* 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.
*/
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;
}
/*