linux-kernel - Re: [PATCH v2 28/39] x86/ibt,xen: Sprinkle the ENDBR

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Date:   Thu, 24 Feb 2022 16:54:40 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH v2 28/39] x86/ibt,xen: Sprinkle the ENDBR

On Thu, Feb 24, 2022 at 03:52:06PM +0100, Peter Zijlstra wrote:
> +++ b/arch/x86/xen/xen-head.S
> @@ -25,8 +25,11 @@
>  SYM_CODE_START(hypercall_page)
>  	.rept (PAGE_SIZE / 32)
>  		UNWIND_HINT_FUNC
> -		.skip 31, 0x90
> -		RET
> +		ANNOTATE_NOENDBR
> +		/*
> +		 * Xen will write the hypercall page, and sort out ENDBR.
> +		 */
> +		.skip 32, 0xcc

I seem to remember this UNWIND_HINT_FUNC was only there to silence
warnings because of the ret.  With the ret gone, maybe the hint can be
dropped as well.

-- 
Josh