linux-kernel - Re: [PATCH] x86/idt: Make sure idt

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Message-ID: <20200720161112.GB620@8bytes.org>
Date:   Mon, 20 Jul 2020 18:11:12 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>, hpa@...or.com,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/idt: Make sure idt_table takes a whole page

On Sun, Jul 19, 2020 at 12:39:44PM +0200, Thomas Gleixner wrote:
> The right fix is trivial. See below.
> 
> Thanks,
> 
>         tglx
> ----
>  arch/x86/kernel/vmlinux.lds.S     |    1 +
>  include/asm-generic/vmlinux.lds.h |    1 +
>  2 files changed, 2 insertions(+)
> 
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -358,6 +358,7 @@ SECTIONS
>  	.bss : AT(ADDR(.bss) - LOAD_OFFSET) {
>  		__bss_start = .;
>  		*(.bss..page_aligned)
> +		. = ALIGN(PAGE_SIZE);
>  		*(BSS_MAIN)
>  		BSS_DECRYPTED
>  		. = ALIGN(PAGE_SIZE);
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -738,6 +738,7 @@
>  	.bss : AT(ADDR(.bss) - LOAD_OFFSET) {				\
>  		BSS_FIRST_SECTIONS					\
>  		*(.bss..page_aligned)					\
> +		. = ALIGN(PAGE_SIZE);					\
>  		*(.dynbss)						\
>  		*(BSS_MAIN)						\
>  		*(COMMON)						\

I thougt about that too (and doing the same for .data..page_aligned),
but decided that 'page_aligned' does not imply 'page_sized', so that
putting other variables on the same page is fine in general and saves
some memory. The problem why it breaks here is only because x86 maps a
variabe which is not page-sized RO, so my thinking was that it should be
fixed right there, at the variable.

But if the above is fine too I prepare a patch which also aligns the end
of .data..page_aligned.

Thanks,

	Joerg