From: hpa@zytor•com (H. Peter Anvin)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 0/3] Batched user access support
Date: Fri, 18 Dec 2015 10:33:25 -0800 [thread overview]
Message-ID: <56745175.9010006@zytor.com> (raw)
In-Reply-To: <20151218111346.GF30483@arm.com>
On 12/18/15 03:13, Will Deacon wrote:
>
> From an implementation and performance point of view, this can certainly
> be used by arm64. My only concern is that we increase the region where
> PAN is disabled (that is, user accesses are permitted). Currently, that's
> carefully restricted to the single userspace access, but now it could
> easily include accesses to the kernel stack, perhaps even generated as
> a result of compiler spills.
>
> I'm pretty unimaginative when it comes to security exploits, but that
> does sound worse than the current implementation from a security
> perspective.
>
It is, but it is a tradeoff. It is way better than opening it up for
the entire kernel. In the end the only real way to avoid this is
compiler support, which I *have* discussed for x86 with the gcc people.
gcc could avoid the back-to-back on and off and even batch accesses by
moving them into registers.
-hpa
next prev parent reply other threads:[~2015-12-18 18:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-17 18:33 [PATCH 0/3] Batched user access support Linus Torvalds
2015-12-18 9:44 ` Ingo Molnar
2015-12-18 17:06 ` Linus Torvalds
2015-12-18 11:13 ` Will Deacon
2015-12-18 18:33 ` H. Peter Anvin [this message]
2015-12-18 18:43 ` Linus Torvalds
2015-12-18 19:56 ` Russell King - ARM Linux
2015-12-18 20:18 ` Linus Torvalds
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