linux-kernel - [PATCH 2/3] x86/shstk: Remove useless clone error handling

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Message-Id: <20230908203655.543765-3-rick.p.edgecombe@intel.com>
Date:   Fri,  8 Sep 2023 13:36:54 -0700
From:   Rick Edgecombe <rick.p.edgecombe@...el.com>
To:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, hjl.tools@...il.com,
        linux-kernel@...r.kernel.org
Cc:     rick.p.edgecombe@...el.com
Subject: [PATCH 2/3] 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")
Tested-by: H.J. Lu <hjl.tools@...il.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.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 9f0909142a0a..b6f4e8399fca 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;
 }
 
-- 
2.34.1