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Re: [Xen-devel] SpectreV1+L1TF Patch Series
- To: Norbert Manthey <nmanthey@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 24 Jan 2019 21:05:22 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Martin Pohlack <mpohlack@xxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, David Woodhouse <dwmw@xxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Martin Mazein <amazein@xxxxxxxxx>, Julian Stecklina <jsteckli@xxxxxxxxx>, Bjoern Doebel <doebel@xxxxxxxxx>
- Delivery-date: Thu, 24 Jan 2019 21:05:49 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 23/01/2019 11:51, Norbert Manthey wrote:
> Dear all,
>
> This patch series attempts to mitigate the issue that have been raised in the
> XSA-289 (https://xenbits.xen.org/xsa/advisory-289.html). To block speculative
> execution on Intel hardware, an lfence instruction is required to make sure
> that selected checks are not bypassed. Speculative out-of-bound accesses can
> be prevented by using the array_index_nospec macro.
>
> The lfence instruction should be added on x86 platforms only. To not affect
> platforms that are not affected by the L1TF vulnerability, the lfence
> instruction is patched in via alternative patching on Intel CPUs only.
> Furthermore, the compile time configuration allows to choose how to protect
> the
> evaluation of conditions with the lfence instruction.
Hello,
First of all, I've dusted off an old patch of mine and made it
speculatively safe.
https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=9e92acf1b752dfdfb294234b32d1fa9f55bfdc0f
Using the new domain_vcpu() helper should tidy up quite a few patches in
the series.
Next, to the ordering of patches.
Please introduce the Kconfig variable(s) first. I'll follow up on that
thread about options.
Next, introduce a new synthetic feature bit to cause patching to occur,
and logic to trigger it in appropriate circumstances. Look through the
history of include/asm-x86/cpufeatures.h to see some examples from the
previous speculative mitigation work. In particular, you'll need a
command line parameter to control the use of this functionality when it
is compiled in.
Next, introduce eval_nospec(). To avoid interfering with other
architectures, you probably want something like this:
xen/nospec.h contains:
/*
* Evaluate a condition in a speculation-safe way.
* Stub implementation for builds which don't care.
*/
#ifndef eval_nospec
#define eval_nospec(x) (x)
#endif
and something containing x86's implementation. TBH, I personally think
asm/nospec.h is overdue for introducing now.
~Andrew
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