linux-kernel - Re: [PATCH v2 01/15] x86, kaslr: Use init_size instead of run

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Message-ID: <CAE9FiQXRyO1aej7_JOfUfG7h-qrFHfukEP+9JxYm5+e9s4-Zpg@mail.gmail.com>
Date:	Fri, 6 Mar 2015 16:52:29 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Matt Fleming <matt.fleming@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Borislav Petkov <bp@...e.de>, Baoquan He <bhe@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Junjie Mao <eternal.n08@...il.com>
Subject: Re: [PATCH v2 01/15] x86, kaslr: Use init_size instead of run_size

On Fri, Mar 6, 2015 at 11:56 AM, Kees Cook <keescook@...omium.org> wrote:
> On Fri, Mar 6, 2015 at 11:28 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> Okay, I've proven this to myself now. :) I think it would be valuable
> to call out that brk and bss are included in the _end calculation. For
> others:
...
> So, _end - _text does equal _text + bss offset + bss size + brk size
>
> Thanks! It'll be nice to lose the run_size hack. Adding some
> documentation to the code here would help others in the future trying
> to find this value, I think. :)

in arch/x86/kernel/vmlinux.lds.S, we have

        /* BSS */
        . = ALIGN(PAGE_SIZE);
        .bss : AT(ADDR(.bss) - LOAD_OFFSET) {
                __bss_start = .;
                *(.bss..page_aligned)
                *(.bss)
                . = ALIGN(PAGE_SIZE);
                __bss_stop = .;
        }

        . = ALIGN(PAGE_SIZE);
        .brk : AT(ADDR(.brk) - LOAD_OFFSET) {
                __brk_base = .;
                . += 64 * 1024;         /* 64k alignment slop space */
                *(.brk_reservation)     /* areas brk users have reserved */
                __brk_limit = .;
        }

        _end = .;

so _end already cover bss and brk.
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