linux-kernel - Re: [PATCH] x86, kaslr: Prevent .bss from overlaping initrd

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Message-ID: <CAGXu5jL94ADSu=PAsbfhpiTc4iK1YCWiQ679BoHHRkhHBtekAQ@mail.gmail.com>
Date:	Fri, 31 Oct 2014 09:14:39 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Eternal <eternal.n08@...il.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, kaslr: Prevent .bss from overlaping initrd

On Fri, Oct 31, 2014 at 12:20 AM, Eternal <eternal.n08@...il.com> wrote:
> Kees Cook <keescook@...omium.org> writes:
> I use the following function to print an arbitrary number in hexadecimal
> in aslr.c and misc.c:
>
> void print_hex(unsigned long value) {
>         char c[2];
>         int i;
>
>         c[1] = '\0';
>         for (i = 60; i >= 0; i -= 4) {
>                 unsigned long digit = (addr >> i) & 0xf;
>                 if (digit <= 9) {
>                         c[0] = '0' + digit;
>                 } else {
>                         c[0] = 'a' + (digit - 10);
>                 }
>                 debug_putstr(c);
>         }
> }

Hah! Yes, this is nearly line-for-line identical to a similar function
I wrote when debugging kASLR during its development. :) I had asked
because I was hoping I wasn't missing some existing way to print hex
values. :)

I will send that, since we clearly keep needing this functionality.

>> Should mkpiggy.c do the work itself instead of taking an argument?
>
> Both ways are ok to me. I'm not sure which way is better, though.

Yeah, after spending time looking at it, your way seemed the cleanest.

-Kees

-- 
Kees Cook
Chrome OS Security
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