Re: [PATCH v27 24/31] x86/cet/shstk: Handle thread shadow stack

From: Yu, Yu-cheng
Date: Tue May 25 2021 - 11:05:45 EST

On 5/22/2021 4:39 PM, Andy Lutomirski wrote:
On Fri, May 21, 2021 at 3:14 PM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 5ea2b494e9f9..8e5f772181b9 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -71,6 +71,53 @@ int shstk_setup(void)
return 0;

+int shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long clone_flags,
+ unsigned long stack_size)


+ state = get_xsave_addr(&tsk->thread.fpu.state.xsave, XFEATURE_CET_USER);
+ if (!state)
+ return -EINVAL;

The get_xsave_addr() API is horrible, and we already have one
egregiously buggy instance in the kernel. Let's not add another
dubious use case.

If state == NULL, this means that CET_USER is in its init state.
CET_USER in the init state should behave identically regardless of
whether XINUSE[CET_USER] is set. Can you please adjust this code

I will work on that.