linux-kernel - Re: [PATCH 2/4] KASLR: Parse all memmap entries in cmdline

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Message-ID: <CAGXu5jJkZG86ad8ovbqTboeHDBzEHXay=ZWE69rXamTqMC7Keg@mail.gmail.com>
Date:   Tue, 18 Apr 2017 16:32:32 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Dave Young <dyoung@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 2/4] KASLR: Parse all memmap entries in cmdline

On Tue, Apr 18, 2017 at 3:52 PM, Baoquan He <bhe@...hat.com> wrote:
> On 04/18/17 at 01:22pm, Kees Cook wrote:
>> > +#define COMMAND_LINE_SIZE 256
>> > +static int handle_mem_memmap(void)
>> > +{
>> > +       char *args = (char *)get_cmd_line_ptr();
>> > +       char tmp_cmdline[COMMAND_LINE_SIZE];
>>
>> Can't this use a dynamic allocation instead of the 256 limit?
>
> This is in boot/compressed code, no mm allocator built yet? Am I right?

misc.c uses malloc for phdrs, and the boot_heap is create to build an
area for those calls, see include/linux/decompress/mm.h. I *think* it
should be safe to use malloc here. It should be a pretty small
allocation normally.

-Kees

-- 
Kees Cook
Pixel Security