linux-kernel - Re: [PATCH v3 07/59] x86: Sanitize linker script

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Message-ID: <Y0BN7PDOqB1vsBih@zn.tnic>
Date:   Fri, 7 Oct 2022 18:03:56 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v3 07/59] x86: Sanitize linker script

On Thu, Sep 15, 2022 at 01:10:46PM +0200, Peter Zijlstra wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The section ordering in the text section is more than suboptimal:
> 
>     ALIGN_ENTRY_TEXT_BEGIN
>     ENTRY_TEXT
>     ALIGN_ENTRY_TEXT_END
>     SOFTIRQENTRY_TEXT
>     STATIC_CALL_TEXT
>     INDIRECT_THUNK_TEXT
> 
> ENTRY_TEXT is in a seperate PMD so it can be mapped into the cpu entry area

s/seperate/separate/g

That's tglx's favourite spelling of "separate" :-)

> when KPTI is enabled. That means the sections after it are also in a
> seperate PMD. That's wasteful especially as the indirect thunk text is a
  ^^^^^^^^

ditto.


> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -132,18 +132,19 @@ SECTIONS
>  		CPUIDLE_TEXT
>  		LOCK_TEXT
>  		KPROBES_TEXT
> -		ALIGN_ENTRY_TEXT_BEGIN
> -		ENTRY_TEXT
> -		ALIGN_ENTRY_TEXT_END
>  		SOFTIRQENTRY_TEXT
> -		STATIC_CALL_TEXT
> -		*(.gnu.warning)
> -
>  #ifdef CONFIG_RETPOLINE
>  		__indirect_thunk_start = .;
>  		*(.text.__x86.*)
>  		__indirect_thunk_end = .;
>  #endif

<--- might wanna put a comment here so that people don't slap some new
sections underneath it.

> +		STATIC_CALL_TEXT
> +
> +		ALIGN_ENTRY_TEXT_BEGIN
> +		ENTRY_TEXT
> +		ALIGN_ENTRY_TEXT_END
> +		*(.gnu.warning)
> +
>  	} :text =0xcccc
>  
>  	/* End of text section, which should occupy whole number of pages */
> 
> 

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette