linux-kernel - Re: [PATCH 1/2] x86/boot: fix KASL when memmap range manipulation is used

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Message-ID: <ciirm8zhr2ira8.fsf@u54ee758033e858cfa736.ant.amazon.com>
Date:   Mon, 11 Feb 2019 10:54:39 +0100
From:   Julian Stecklina <jsteckli@...zon.de>
To:     Baoquan He <bhe@...hat.com>
Cc:     Julian Stecklina <js@...en8.de>, <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
        <jschoenh@...zon.de>
Subject: Re: [PATCH 1/2] x86/boot: fix KASL when memmap range manipulation is used

Baoquan He <bhe@...hat.com> writes:

> On 01/30/19 at 05:40pm, Julian Stecklina wrote:
>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>> index 9ed9709..5657e34 100644
>> --- a/arch/x86/boot/compressed/kaslr.c
>> +++ b/arch/x86/boot/compressed/kaslr.c
>> @@ -155,6 +155,12 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
>>  	case '#':
>>  	case '$':
>>  	case '!':
>> +		/*
>> +		 * % would need some more complex parsing, because regions might
>> +		 * actually become usable for KASLR, but the simple way of
>> +		 * ignoring anything that is mentioned in % works for now.
>> +		 */
>
> This seems to make thing more complicated even though have to. One
> concern is whether we need to check the oldtype|newtype , e.g
> oldtype=reserverd, newtype=RAM, is it possible to set like that?

With the above patch the boot code will avoid using any region targeted
by % for KASLR. This does mean regions that are changed to be usable via
% are not taken into account.

Julian