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authorEric W. Biederman <ebiederm@xmission.com>2022-04-29 11:09:11 -0500
committerEric W. Biederman <ebiederm@xmission.com>2022-05-11 14:33:54 -0500
commit16cc1bc67de88be19fa595f4645506ea2ac106d2 (patch)
tree51cc5348aae9663f9b8895d570e0f2d30b559784 /kernel
parent4a3d2717d140401df7501a95e454180831a0c5af (diff)
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ptrace: Remove arch_ptrace_attach
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 aa91a2e90044 ("[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 d79fdd6d96f4 ("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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/ptrace.c18
1 files changed, 0 insertions, 18 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index ccc4b465775b..da30dcd477a0 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -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;
}