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Re: [Xen-devel] [PATCH L1TF v9 7/7] common/grant_table: block speculative out-of-bound accesses
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Norbert Manthey <nmanthey@xxxxxxxxx>
- Date: Tue, 12 Mar 2019 11:36:25 +0100
- Autocrypt: addr=nmanthey@xxxxxxxxx; prefer-encrypt=mutual; keydata= mQINBFoJQc0BEADM8Z7hB7AnW6ErbSMsYkKh4HLAPfoM+wt7Fd7axHurcOgFJEBOY2gz0isR /EDiGxYyTgxt5PZHJIfra0OqXRbWuLltbjhJACbu35eaAo8UM4/awgtYx3O1UCbIlvHGsYDg kXjF8bBrVjPu0+g55XizX6ot/YPAgmWTdH8qXoLYVZVWJilKlTqpYEVvarSn/BVgCbIsQIps K93sOTN9eJKDSqHvbkgKl9XG3WsZ703431egIpIZpfN0zZtzumdZONb7LiodcFHJ717vvd89 3Hv2bYv8QLSfYsZcSnyU0NVzbPhb1WtaduwXwNmnX1qHJuExzr8EnRT1pyhVSqouxt+xkKbV QD9r+cWLChumg3g9bDLzyrOTlEfAUNxIqbzSt03CRR43dWgfgGiLDcrqC2b1QR886WDpz4ok xX3fdLaqN492s/3c59qCGNG30ebAj8AbV+v551rsfEba+IWTvvoQnbstc6vKJCc2uG8rom5o eHG/bP1Ug2ht6m/0uWRyFq9C27fpU9+FDhb0ZsT4UwOCbthe35/wBZUg72zDpT/h5lm64G6C 0TRqYRgYcltlP705BJafsymmAXOZ1nTCuXnYAB9G9LzZcKKq5q0rP0kp7KRDbniirCUfp7jK VpPCOUEc3tS1RdCCSeWNuVgzLnJdR8W2h9StuEbb7hW4aFhwRQARAQABtCROb3JiZXJ0IE1h bnRoZXkgPG5tYW50aGV5QGFtYXpvbi5kZT6JAj0EEwEIACcFAloJQc0CGyMFCQlmAYAFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AACgkQZ+8yS8zN62ajmQ/6AlChoY5UlnUaH/jgcabyAfUC XayHgCcpL1SoMKvc2rCA8PF0fza3Ep2Sw0idLqC/LyAYbI6gMYavSZsLcsvY6KYAZKeaEriG 7R6cSdrbmRcKpPjwvv4iY6G0DBTeaqfNjGe1ECY8u522LprDQVquysJIf3YaEyxoK/cLSb0c kjzpqI1P9Vh+8BQb5H9gWpakbhFIwbRGHdAF1roT7tezmEshFS0IURJ2ZFEI+ZgWgtl1MBwN sBt65im7x5gDo25h8A5xC9gLXTc4j3tk+3huaZjUJ9mCbtI12djVtspjNvDyUPQ5Mxw2Jwar C3/ZC+Nkb+VlymmErpnEUZNltcq8gsdYND4TlNbZ2JhD0ibiYFQPkyuCVUiVtimXfh6po9Yt OkE0DIgEngxMYfTTx01Zf6iwrbi49eHd/eQQw3zG5nn+yZsEG8UcP1SCrUma8p93KiKOedoL n43kTg4RscdZMjj4v6JkISBcGTR4uotMYP4M0zwjklnFXPmrZ6/E5huzUpH9B7ZIe/SUu8Ur xww/4dN6rfqbNzMxmya8VGlEQZgUMWcck+cPrRLB09ZOk4zq9i/yaHDEZA1HNOfQ9UCevXV5 7seXSX7PCY6WDAdsT3+FuaoQ7UoWN3rdpb+064QKZ0FsHeGzUd7MZtlgU4EKrh25mTSNZYRs nTz2zT/J33e5Ag0EWglBzQEQAKioD1gSELj3Y47NE11oPkzWWdxKZdVr8B8VMu6nVAAGFRSf Dms4ZmwGY27skMmOH2srnZyTfm9FaTKr8RI+71Fh9nfB9PMmwzA7OIY9nD73/HqPywzTTleG MlALmnuY6xFRSDmqmvxDHgWyzB4TgPWt8+hW3+TJKCx2RgLAdSuULZla4lia+NlS8WNRUDGK sFJCCB3BW5I/cocfpBEUqLbbmnPuD9UKpEnFcYWD9YaDNcBTjSc7iDsvtpdrBXg5VETOz/TQ /CmVs9h/5zug8O4bXxHEEJpCAxs4cGKxowBqx/XJfkwdWeo/LdaeR+LRbXvq4A32HSkyj9sV vygwt2OFEk493JGik8qtAA/oPvuqVPJGacxmZ7zKR12c0mnKCHiexFJzFbC7MSiUhhe8nNiM p6Sl6EZmsTUXhV2bd2M12Bqcss3TTJ1AcW04T4HYHVCSxwl0dVfcf3TIaH0BSPiwFxz0FjMk 10umoRvUhYYoYpPFCz8dujXBlfB8q2tnHltEfoi/EIptt1BMNzTYkHKArj8Fwjf6K+nQ3a8p 1cWfkYpA5bRqbhbplzpa0u1Ex0hZk6pka0qcVgqmH31O2OcSsqeKfUfHkzj3Q6dmuwm1je/f HWH9N1gDPEp1RB5bIxPnOG1Z4SNl9oVQJhc4qoJiqbvkciivYcH7u2CBkboFABEBAAGJAiUE GAEIAA8FAloJQc0CGwwFCQlmAYAACgkQZ+8yS8zN62YU9Q//WTnN28aBX1EhDidVho80Ql2b tV1cDRh/vWTcM4qoM8vzW4+F/Ive6wDVAJ7zwAv8F8WPzy+acxtHLkyYk14M6VZ1eSy0kV0+ RZQdQ+nPtlb1MoDKw2N5zhvs8A+WD8xjDIA9i21hQ/BNILUBINuYKyR19448/41szmYIEhuJ R2fHoLzNdXNKWQnN3/NPTuvpjcrkXKJm2k32qfiys9KBcZX8/GpuMCc9hMuymzOr+YlXo4z4 1xarEJoPOQOXnrmxN4Y30/qmf70KHLZ0GQccIm/o/XSOvNGluaYv0ZVJXHoCnYvTbi0eYvz5 OfOcndqLOfboq9kVHC6Yye1DLNGjIVoShJGSsphxOx2ryGjHwhzqDrLiRkV82gh6dUHKxBWd DXfirT8a4Gz/tY9PMxan67aSxQ5ONpXe7g7FrfrAMe91XRTf50G3rHb8+AqZfxZJFrBn+06i p1cthq7rJSlYCqna2FedTUT+tK1hU9O0aK4ZYYcRzuTRxjd4gKAWDzJ1F/MQ12ftrfCAvs7U sVbXv2TndGIleMnheYv1pIrXEm0+sdz5v91l2/TmvkyyWT8s2ksuZis9luh+OubeLxHq090C hfavI9WxhitfYVsfo2kr3EotGG1MnW+cOkCIX68w+3ZS4nixZyJ/TBa7RcTDNr+gjbiGMtd9 pEddsOqYwOs=
- Cc: Juergen Gross <jgross@xxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Martin Pohlack <mpohlack@xxxxxxxxx>, wipawel@xxxxxxxxx, Julien Grall <julien.grall@xxxxxxx>, David Woodhouse <dwmw@xxxxxxxxxxxx>, "Martin Mazein\(amazein\)" <amazein@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Julian Stecklina <jsteckli@xxxxxxxxx>, Bjoern Doebel <doebel@xxxxxxxxx>
- Delivery-date: Tue, 12 Mar 2019 10:36:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 3/5/19 17:38, Jan Beulich wrote:
>>>> On 27.02.19 at 17:13, <nmanthey@xxxxxxxxx> wrote:
>> Speculative execution is not blocked in case one of the following
>> properties is true:
>> - path cannot be triggered by the guest
>> - path does not return to the guest
>> - path does not result in an out-of-bound access
>> - path cannot be executed repeatedly
>> Only the combination of the above properties allows to actually leak
>> continuous chunks of memory. Therefore, we only add the penalty of
>> protective mechanisms in case a potential speculative out-of-bound
>> access matches all the above properties.
> While this is all fine, how do I match which of the reasons applies to
> which of (in particular) the gt_version checks left alone? As said, the
> reasoning here should specifically be detailed so it can be used as a
> guiding reference when adding further conditionals to the code down
> the road. And of course review is (more) difficult this way as well, as
> (judging from prior conversations) we don't seem to necessarily
> agree in our views in all places, and hence to discuss a possibly
> questionable decision others also need to understand which of the
> criteria you considered to match in the specific case.
I listed the reasons to use above (and in the commit message). I will
extend the commit message and give a reason for each version comparison,
similarly to a prior email I sent.
In my opinion, the commit message for fixing the problems we found in
that file should not be a tutorial on how to identify and fix potential
speculative out-of-bound accesses. While I agree that teaching more
people how to judge whether a certain piece of code might lead to
information leak via speculative execution, I would not use a commit
message to get that covered.
Best,
Norbert
>
> Jan
>
>
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrer: Christian Schlaeger, Ralf Herbrich
Ust-ID: DE 289 237 879
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