From: David Laight <David.Laight@ACULAB.COM>
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Subject: RE: [tip:x86/pti] x86/retpoline: Fill RSB on context switch for affected CPUs
Date: Mon, 15 Jan 2018 14:35:34 +0000 [thread overview]
Message-ID: <a4e50e6701554400afd44767c1812ccd@AcuMS.aculab.com> (raw)
In-Reply-To: <tip-a0ab15c0fb68e202bebd9b17fa49fd7ec48975b3@git.kernel.org>
From: David Woodhouse
> Sent: 14 January 2018 17:04
> x86/retpoline: Fill RSB on context switch for affected CPUs
>
> On context switch from a shallow call stack to a deeper one, as the CPU
> does 'ret' up the deeper side it may encounter RSB entries (predictions for
> where the 'ret' goes to) which were populated in userspace.
>
> This is problematic if neither SMEP nor KPTI (the latter of which marks
> userspace pages as NX for the kernel) are active, as malicious code in
> userspace may then be executed speculatively.
...
Do we have a guarantee that all cpu actually detect the related RSB underflow?
It wouldn't surprise me if at least some cpu just let it wrap.
This would means that userspace would see return predictions based
on the values the kernel 'stuffed' into the RSB to fill it.
Potentially this leaks a kernel address to userspace.
David
next prev parent reply other threads:[~2018-01-15 14:35 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 17:49 [PATCH] x86/retpoline: Fill RSB on context switch for affected CPUs David Woodhouse
2018-01-12 18:02 ` Andi Kleen
2018-01-12 18:23 ` David Woodhouse
2018-01-12 18:05 ` Andrew Cooper
2018-01-12 18:56 ` David Woodhouse
2018-01-12 23:41 ` Josh Poimboeuf
2018-01-14 11:39 ` Thomas Gleixner
2018-01-14 17:04 ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-15 14:35 ` David Laight [this message]
2018-01-15 14:39 ` David Woodhouse
2018-01-15 14:42 ` Arjan van de Ven
2018-01-15 20:03 ` Kees Cook
2018-01-14 23:37 ` tip-bot for David Woodhouse
2018-01-15 0:05 ` Andi Kleen
2018-01-15 0:09 ` Andi Kleen
2018-01-15 10:13 ` David Woodhouse
2018-03-09 13:12 ` Maciej S. Szmigiero
2018-03-09 15:14 ` Andi Kleen
2018-03-09 15:33 ` Maciej S. Szmigiero
2018-03-09 15:38 ` Woodhouse, David
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