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From: "H. Peter Anvin" <hpa@zytor.com>
To: Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@linux.intel.com>,
	"linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/kaslr] x86, kaslr: Provide randomness functions
Date: Mon, 11 Nov 2013 11:37:11 -0800	[thread overview]
Message-ID: <528131E7.2060509@zytor.com> (raw)
In-Reply-To: <CAGXu5jL96B4+McO=K9dptu81m+bdKWOZ8YS9x7+SZxkjfUsg9Q@mail.gmail.com>

On 11/11/2013 11:32 AM, Kees Cook wrote:
>>>
>>> Why aren't the 3 sources of entropy XOR-ed together?
> 
> Ah, excellent suggestion. There's no reason they couldn't be. I can
> rework that function to do that.
> 
>>> Also, we talked about also adding system dependent entropy sources, such
>>> as memory layout or the DMI table - none of that seems to have happened.
> 
> It seemed like those things didn't contribute as much entropy as the 3
> already in use, but I could investigate how to distill those things
> down into entropy. Perhaps just XORing the start and length of every
> e820 area? DMI I'll need to dig into...
> 

DMI and ACPI are relatively straightforward: they are really just blocks
of memory with magic pointers.  Since you don't actually need to parse
them, it is mostly just a matter of finding those blocks of memory and
hashing them.

You could also hash the BDA - the first 0x500 bytes of memory - although
that starts to get into the "what about weird nontraditional platforms"
space.

A *MAJOR* issue with DMI and ACPI is that the way they are located is
firmware dependent: there is a search algorithm defined for BIOS
platforms, whereas on EFI I believe it requires doing runtime calls to
find things.

Of course, perhaps we could just hash struct boot_params as a starting
point?

	-hpa


  reply	other threads:[~2013-11-11 19:37 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-11  0:18 [PATCH v8 0/6] Kernel base address randomization Kees Cook
2013-10-11  0:18 ` [kernel-hardening] " Kees Cook
2013-10-11  0:18 ` [PATCH v8 1/6] x86, boot: move CPU flags out of cpucheck Kees Cook
2013-10-11  0:18   ` [kernel-hardening] " Kees Cook
2013-10-13 12:01   ` [tip:x86/kaslr] x86, boot: Move " tip-bot for Kees Cook
2013-10-13 12:02   ` [tip:x86/kaslr] x86, boot: Rename get_flags() and check_flags() to *_cpuflags() tip-bot for H. Peter Anvin
2013-10-11  0:18 ` [PATCH v8 2/6] x86, kaslr: return location from decompress_kernel Kees Cook
2013-10-11  0:18   ` [kernel-hardening] " Kees Cook
2013-10-13 12:01   ` [tip:x86/kaslr] x86, kaslr: Return " tip-bot for Kees Cook
2013-10-11  0:18 ` [PATCH v8 3/6] x86, kaslr: provide randomness functions Kees Cook
2013-10-11  0:18   ` [kernel-hardening] " Kees Cook
2013-10-13 12:01   ` [tip:x86/kaslr] x86, kaslr: Provide " tip-bot for Kees Cook
2013-11-11 18:20     ` Ingo Molnar
2013-11-11 18:31       ` Ingo Molnar
2013-11-11 19:32         ` Kees Cook
2013-11-11 19:37           ` H. Peter Anvin [this message]
2013-11-11 20:07             ` Ingo Molnar
2013-11-11 20:11               ` Kees Cook
2013-11-11 20:16                 ` H. Peter Anvin
2013-11-11 19:27       ` H. Peter Anvin
2013-11-11 19:37         ` Kees Cook
2013-11-11 19:42           ` H. Peter Anvin
2013-11-11 19:58             ` Ingo Molnar
2013-11-11 20:04               ` H. Peter Anvin
2013-11-11 20:09                 ` Ingo Molnar
2013-11-13 18:16       ` Pavel Machek
2013-11-13 18:40         ` H. Peter Anvin
2013-11-13 23:23           ` Pavel Machek
2013-11-13 23:25             ` H. Peter Anvin
2013-10-11  0:18 ` [PATCH v8 4/6] x86, kaslr: select random position from e820 maps Kees Cook
2013-10-11  0:18   ` [kernel-hardening] " Kees Cook
2013-10-13 12:01   ` [tip:x86/kaslr] x86, kaslr: Select " tip-bot for Kees Cook
2013-10-11  0:18 ` [PATCH v8 5/6] x86, kaslr: report kernel offset on panic Kees Cook
2013-10-11  0:18   ` [kernel-hardening] " Kees Cook
2013-10-13 12:01   ` [tip:x86/kaslr] x86, kaslr: Report " tip-bot for Kees Cook
2013-10-11  0:18 ` [PATCH v8 6/6] x86, kaslr: raise max positions to 1GiB on x86_64 Kees Cook
2013-10-11  0:18   ` [kernel-hardening] " Kees Cook
2013-10-13 12:02   ` [tip:x86/kaslr] x86, kaslr: Raise the maximum virtual address to -1 GiB " tip-bot for Kees Cook

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