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Eric W. Biederman
16cc1bc67d
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 commitaa91a2e900("[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 commitd79fdd6d96("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.