x86/shstk: Remove useless clone error handling

When clone fails after the shadow stack is allocated, any allocated shadow
stack is cleaned up in exit_thread() in copy_process(). So the logic in
copy_thread() is unneeded, and also will not handle failures that happen
outside of copy_thread().

In addition, since there is a second attempt to unmap the same shadow
stack, there is a race where an newly mapped region could get unmapped.

So remove the logic in copy_thread() and rely on exit_thread() to handle
clone failure.

Fixes: b2926a36b97a ("x86/shstk: Handle thread shadow stack")
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: H.J. Lu <hjl.tools@gmail.com>
Link: https://lore.kernel.org/all/20230908203655.543765-3-rick.p.edgecombe%40intel.com

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9f09091..b6f4e83 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -257,13 +257,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
        if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
                io_bitmap_share(p);
 
-       /*
-        * If copy_thread() if failing, don't leak the shadow stack possibly
-        * allocated in shstk_alloc_thread_stack() above.
-        */
-       if (ret)
-               shstk_free(p);
-
        return ret;
 }