[tip: x86/urgent] x86/shstk: Remove useless clone error handling

[tip-bot2 for Rick Edgecombe]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     748c90c693363d05c6b2f3915edc7999a2f71837
Gitweb:        https://git.kernel.org/tip/748c90c693363d05c6b2f3915edc7999a2f71837
Author:        Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
AuthorDate:    Fri, 08 Sep 2023 13:36:54 -07:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Tue, 19 Sep 2023 09:18:34 -07:00

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@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Tested-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Link: https://lore.kernel.org/all/20230908203655.543765-3-rick.p.edgecombe%40intel.com
---
 arch/x86/kernel/process.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9f09091..b6f4e83 100644
--- 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;
 }