linux-kernel - Re: [PATCH v2 07/39] x86/entry: Sprinkle ENDBR dust

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Date:   Thu, 24 Feb 2022 14:37:28 -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 07/39] x86/entry: Sprinkle ENDBR dust

On Thu, Feb 24, 2022 at 03:51:45PM +0100, Peter Zijlstra wrote:
> Kernel entry points should be having ENDBR on for IBT configs.
> 
> The SYSCALL entry points are found through taking their respective
> address in order to program them in the MSRs, while the exception
> entry points are found through UNWIND_HINT_IRET_REGS.
> 
> The rule is that any UNWIND_HINT_IRET_REGS at sym+0 should have an
> ENDBR, see the later objtool ibt validation patch.

Could the "rule" be changed to only check global syms?  It seems
unlikely a local symbol would need ENDBR.

Then you wouldn't need this annotation:

>  SYM_CODE_START_LOCAL(early_idt_handler_common)
> +	UNWIND_HINT_IRET_REGS offset=16
> +	ANNOTATE_NOENDBR
>  	/*
>  	 * The stack is the hardware frame, an error code or zero, and the
>  	 * vector number.

-- 
Josh