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From: Dave Hansen <>
To: Michael Sammler <>, Jann Horn <>
Cc:, Kees Cook <>,
	Rik van Riel <>,
	Linux API <>,
	Dave Hansen <>,, Andy Lutomirski <>,
Subject: Re: [RFC PATCH] seccomp: Add protection keys into seccomp_data
Date: Mon, 29 Oct 2018 10:07:09 -0700
Message-ID: <> (raw)
In-Reply-To: <>

On 10/29/18 10:02 AM, Michael Sammler wrote:
>>> Also, I'm not sure the kernel provides the PKRU guarantees you want at
>>> the moment.  Our implementation *probably* works, but it's mostly by
>>> accident.
> I don't know, which guarantees about the PKRU are provided at the
> moment, but the only guarantee needed for this patch is, that the kernel
> does not change the bits of the PKRU register, which belong to pkeys
> allocated by the user program, between the syscall entry and the call to
> secure_computing(). Is there are use case where the kernel would like to
> modify these bits of the PKRU?

We've been talking about doing more lax save/restore of the XSAVE
content (PKRU is part of this content).  We would, for instance, only
restore it when returning to userspace, but PKRU might not be up-to-date
with the value in current->fpu.

It's not a deal-breaker with your approach, it's just something to be
careful of and make sure PKRU is up-to-date before you go use it.

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-29 11:23 Michael Sammler
2018-10-29 16:25 ` Kees Cook
2018-10-29 16:37   ` Dave Hansen
2018-10-29 16:48     ` Jann Horn
2018-10-29 17:02       ` Michael Sammler
2018-10-29 17:07         ` Dave Hansen [this message]
2018-10-29 17:29       ` Dave Hansen
2018-10-29 21:55         ` Michael Sammler
2018-10-29 22:33           ` Dave Hansen
2018-10-30 10:55             ` Michael Sammler
2018-10-29 16:42   ` Jann Horn
2018-10-29 16:48   ` Ram Pai
2018-10-29 17:05     ` Michael Sammler

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