Date: Fri, 15 Apr 2016 12:26:08 -0700 From: Kees Cook <keescook@...omium.org> To: Ingo Molnar <mingo@...nel.org> Cc: Yinghai Lu <yinghai@...nel.org>, Junjie Mao <eternal.n08@...il.com>, Josh Triplett <josh@...htriplett.org>, Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Matt Redfearn <matt.redfearn@...tec.com>, "x86@...nel.org" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Vivek Goyal <vgoyal@...hat.com>, Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org, Dave Young <dyoung@...hat.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v5 07/21] x86, boot: Fix run_size calculation On Fri, Apr 15, 2016 at 1:31 AM, Ingo Molnar <mingo@...nel.org> wrote: > > * Kees Cook <keescook@...omium.org> wrote: > >> From: Yinghai Lu <yinghai@...nel.org> >> >> Currently, the kernel run_size (size of code plus brk and bss) is >> calculated via the shell script arch/x86/tools/calc_run_size.sh. >> It gets the file offset and mem size of for the .bss and .brk sections in >> vmlinux, and adds them as follows: > > 'of for'? > >> So, from this we can see that the existing run_size calculation is >> 0x400000 too high. > > Btw., why is it too high? Were some sections discarded? I'm not sure why it's that specific value, but the old method used the section's ELF _file_ position, not the virtual address, and that seemed to cause the problem. > >> [...] And, as it turns out, the correct run_size is >> actually equal to VO_end - VO_text, which is certainly easier to calculate. >> _end: 0xffffffff8205f000 >> _text:0xffffffff81000000 >> >> 0xffffffff8205f000 - 0xffffffff81000000 = 0x105f000 >> >> As a result, run_size is a simple constant, so we don't need to pass it >> around; we already have voffset.h such things. > > (Typo.) > >> [...] We can share voffset.h >> between misc.c and header.S instead of getting run_size in other ways. >> This patch moves voffset.h creation code to boot/compressed/Makefile, >> and switches misc.c to use the VO_end - VO_text calculation. > > Btw., 'run_size' is a pretty meaningless name, it doesn't really tell us the most > important thing: that this is the complete size of the uncompressed kernel, the > total physically continuous size we need to allocate to it so it can execute? > > So can we rename it to something more expressive, such as kernel_total_size or so? You got it. Thanks again for digging through all this! -Kees -- Kees Cook Chrome OS & Brillo Security
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