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ptrace: Remove arch_ptrace_attach

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The last remaining implementation of arch_ptrace_attach is ia64's
ptrace_attach_sync_user_rbs which was added at the end of 2007 in
commit aa91a2e900 ("[IA64] Synchronize RBS on PTRACE_ATTACH").

Reading the comments and examining the code ptrace_attach_sync_user_rbs
has the sole purpose of saving registers to the stack when ptrace_attach
changes TASK_STOPPED to TASK_TRACED.  In all other cases arch_ptrace_stop
takes care of the register saving.

In commit d79fdd6d96 ("ptrace: Clean transitions between TASK_STOPPED and TRACED")
modified ptrace_attach to wake up the thread and enter ptrace_stop normally even
when the thread starts out stopped.

This makes ptrace_attach_sync_user_rbs completely unnecessary.  So just
remove it.

I read through the code to verify that ptrace_attach_sync_user_rbs is
unnecessary.  What I found is that the code is quite dead.

Reading ptrace_attach_sync_user_rbs it is easy to see that the it does
nothing unless __state == TASK_STOPPED.

Calling arch_ptrace_attach (aka ptrace_attach_sync_user_rbs) after
ptrace_traceme it is easy to see that because we are talking about the
current process the value of __state is TASK_RUNNING.  Which means
ptrace_attach_sync_user_rbs does nothing.

The only other call of arch_ptrace_attach (aka
ptrace_attach_sync_user_rbs) is after ptrace_attach.

If the task is running (and PTRACE_SEIZE is not specified), a SIGSTOP
is sent which results in do_signal_stop setting JOBCTL_TRAP_STOP on
the target task (as it is ptraced) and the target task stopping
in ptrace_stop with __state == TASK_TRACED.

If the task was already stopped then ptrace_attach sets
JOBCTL_TRAPPING and JOBCTL_TRAP_STOP, wakes it out of __TASK_STOPPED,
and waits until the JOBCTL_TRAPPING_BIT is clear.  At which point
the task stops in ptrace_stop.

In both cases there are a couple of funning excpetions such as if the
traced task receiveds a SIGCONT, or is set a fatal signal.

However in all of those cases the tracee never stops in __state
TASK_STOPPED.  Which is a long way of saying that ptrace_attach_sync_user_rbs
is guaranteed never to do anything.

Cc: linux-ia64@vger.kernel.org
Tested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20220505182645.497868-4-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2022-04-29 11:09:11 -05:00
parent 4a3d2717d1
commit 16cc1bc67d
3 changed files with 0 additions and 79 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/ia64/include/asm/ptrace.h
View File

@ -139,10 +139,6 @@ static inline long regs_return_value(struct pt_regs *regs)
#define arch_ptrace_stop_needed() \
(!test_thread_flag(TIF_RESTORE_RSE))
extern void ptrace_attach_sync_user_rbs (struct task_struct *);
#define arch_ptrace_attach(child) \
ptrace_attach_sync_user_rbs(child)
#define arch_has_single_step() (1)
#define arch_has_block_step() (1)

57
arch/ia64/kernel/ptrace.c
View File

@ -617,63 +617,6 @@ void ia64_sync_krbs(void)
unw_init_running(do_sync_rbs, ia64_sync_kernel_rbs);
}
/*
* After PTRACE_ATTACH, a thread's register backing store area in user
* space is assumed to contain correct data whenever the thread is
* stopped. arch_ptrace_stop takes care of this on tracing stops.
* But if the child was already stopped for job control when we attach
* to it, then it might not ever get into ptrace_stop by the time we
* want to examine the user memory containing the RBS.
*/
void
ptrace_attach_sync_user_rbs (struct task_struct *child)
{
int stopped = 0;
struct unw_frame_info info;
/*
* If the child is in TASK_STOPPED, we need to change that to
* TASK_TRACED momentarily while we operate on it. This ensures
* that the child won't be woken up and return to user mode while
* we are doing the sync. (It can only be woken up for SIGKILL.)
*/
read_lock(&tasklist_lock);
if (child->sighand) {
spin_lock_irq(&child->sighand->siglock);
if (READ_ONCE(child->__state) == TASK_STOPPED &&
!test_and_set_tsk_thread_flag(child, TIF_RESTORE_RSE)) {
set_notify_resume(child);
WRITE_ONCE(child->__state, TASK_TRACED);
stopped = 1;
}
spin_unlock_irq(&child->sighand->siglock);
}
read_unlock(&tasklist_lock);
if (!stopped)
return;
unw_init_from_blocked_task(&info, child);
do_sync_rbs(&info, ia64_sync_user_rbs);
/*
* Now move the child back into TASK_STOPPED if it should be in a
* job control stop, so that SIGCONT can be used to wake it up.
*/
read_lock(&tasklist_lock);
if (child->sighand) {
spin_lock_irq(&child->sighand->siglock);
if (READ_ONCE(child->__state) == TASK_TRACED &&
(child->signal->flags & SIGNAL_STOP_STOPPED)) {
WRITE_ONCE(child->__state, TASK_STOPPED);
}
spin_unlock_irq(&child->sighand->siglock);
}
read_unlock(&tasklist_lock);
}
/*
* Write f32-f127 back to task->thread.fph if it has been modified.
*/

18
kernel/ptrace.c
View File

@ -1285,10 +1285,6 @@ int ptrace_request(struct task_struct *child, long request,
return ret;
}
#ifndef arch_ptrace_attach
#define arch_ptrace_attach(child) do { } while (0)
#endif
SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
unsigned long, data)
{
@ -1297,8 +1293,6 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
if (request == PTRACE_TRACEME) {
ret = ptrace_traceme();
if (!ret)
arch_ptrace_attach(current);
goto out;
}
@ -1310,12 +1304,6 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
ret = ptrace_attach(child, request, addr, data);
/*
* Some architectures need to do book-keeping after
* a ptrace attach.
*/
if (!ret)
arch_ptrace_attach(child);
goto out_put_task_struct;
}
@ -1455,12 +1443,6 @@ COMPAT_SYSCALL_DEFINE4(ptrace, compat_long_t, request, compat_long_t, pid,
if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
ret = ptrace_attach(child, request, addr, data);
/*
* Some architectures need to do book-keeping after
* a ptrace attach.
*/
if (!ret)
arch_ptrace_attach(child);
goto out_put_task_struct;
}