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From: Ingo Molnar <mingo@kernel.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Dave Young <dyoung@redhat.com>, Baoquan He <bhe@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	Thomas Garnier <thgarnie@google.com>,
	Kees Cook <keescook@chromium.org>, Borislav Petkov <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Bhupesh Sharma <bhsharma@redhat.com>
Subject: Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization
Date: Fri, 24 Mar 2017 11:36:24 +0100	[thread overview]
Message-ID: <20170324103624.GA6231@gmail.com> (raw)
In-Reply-To: <CAKv+Gu_V_VAWuDtKyOY9RS+cdhi+c5z2a7n2kcXVybvvdmPYBw@mail.gmail.com>


* Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> No. It is the firmware's EFI code, and the virtual translation applied by the OS 
> is made known to the firmware by means of a call into the runtime service 
> SetVirtualAddressMap(). This service can only be called once after each boot, 
> and so kexec kernels are forced to use the same VA mapping for runtime services 
> as the first kernel. This is the whole point of having a VA region reserved for 
> this, so that kexec kernels are guaranteed to be able to use the same VA 
> mapping.

Yes, but it's the kernel's EFI code that determines the area! So my suggestion:

> > Preserving virtual addresses for kexec is a red herring: the randomized offset 
> > could be passed to the kexec-ed kernel just fine.

Would solve the kexec problem, right?

I.e. the first kernel that boots randomizes the address range - and passes that 
offset off to any subsequent kernels.

Turning KASLR off actively degrades that randomization of the kernel virtual 
addresses.

Am I missing anything?

Thanks,

	Ingo

WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Dave Young <dyoung-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Baoquan He <bhe-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>,
	"x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org"
	<x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	"linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	Borislav Petkov <bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Masahiro Yamada
	<yamada.masahiro-uWyLwvC0a2jby3iVrkZq2A@public.gmane.org>,
	Bhupesh Sharma <bhsharma-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization
Date: Fri, 24 Mar 2017 11:36:24 +0100	[thread overview]
Message-ID: <20170324103624.GA6231@gmail.com> (raw)
In-Reply-To: <CAKv+Gu_V_VAWuDtKyOY9RS+cdhi+c5z2a7n2kcXVybvvdmPYBw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>


* Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:

> No. It is the firmware's EFI code, and the virtual translation applied by the OS 
> is made known to the firmware by means of a call into the runtime service 
> SetVirtualAddressMap(). This service can only be called once after each boot, 
> and so kexec kernels are forced to use the same VA mapping for runtime services 
> as the first kernel. This is the whole point of having a VA region reserved for 
> this, so that kexec kernels are guaranteed to be able to use the same VA 
> mapping.

Yes, but it's the kernel's EFI code that determines the area! So my suggestion:

> > Preserving virtual addresses for kexec is a red herring: the randomized offset 
> > could be passed to the kexec-ed kernel just fine.

Would solve the kexec problem, right?

I.e. the first kernel that boots randomizes the address range - and passes that 
offset off to any subsequent kernels.

Turning KASLR off actively degrades that randomization of the kernel virtual 
addresses.

Am I missing anything?

Thanks,

	Ingo

  parent reply	other threads:[~2017-03-24 10:36 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-24  4:59 [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization Baoquan He
2017-03-24  4:59 ` Baoquan He
2017-03-24  8:08 ` Ingo Molnar
2017-03-24  8:08   ` Ingo Molnar
2017-03-24  8:34   ` Baoquan He
2017-03-24  8:34     ` Baoquan He
2017-03-24  8:46     ` Dave Young
2017-03-24  8:46       ` Dave Young
2017-03-24  9:24       ` Ingo Molnar
2017-03-24  9:36         ` Borislav Petkov
2017-03-24  9:37         ` Ard Biesheuvel
2017-03-24  9:37           ` Ard Biesheuvel
2017-03-24  9:40           ` Borislav Petkov
2017-03-24  9:42             ` Ard Biesheuvel
2017-03-24  9:46               ` Borislav Petkov
2017-03-24  9:46                 ` Borislav Petkov
2017-03-24  9:52                 ` Ard Biesheuvel
2017-03-24  9:52                   ` Ard Biesheuvel
2017-03-24 10:36           ` Ingo Molnar [this message]
2017-03-24 10:36             ` Ingo Molnar
2017-03-24 10:42             ` Ard Biesheuvel
2017-03-24 10:54               ` Ingo Molnar
2017-03-24 11:52         ` Baoquan He
2017-03-24  8:53   ` Dave Young
2017-03-24  8:10 ` [tip:x86/urgent] x86/mm/KASLR: Exclude EFI region from KASLR VA space randomization tip-bot for Baoquan He

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