Re: Reverse engineering of Intel branch predictors

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Sujet : Re: Reverse engineering of Intel branch predictors
De : mitchalsup (at) *nospam* aol.com (MitchAlsup1)
Groupes : comp.arch
Date : 01. Nov 2024, 22:21:53
Autres entêtes
Organisation : Rocksolid Light
Message-ID : <6f26c7df4e339b3c2e85ec4b2291f106@www.novabbs.org>
References : 1 2
User-Agent : Rocksolid Light
On Fri, 1 Nov 2024 19:04:38 +0000, Waldek Hebisch wrote:

Thomas Koenig <tkoenig@netcologne.de> wrote:
Seems like Intel branch predictors have been pretty completely
reverse-engineered.  The following paper promises to for very
interesting reading:
>
https://www.usenix.org/conference/usenixsecurity24/presentation/li-luyi
>
I wonder what you think of this...
>
There are more papers on this topic.  There were several papers
on variations of Spectre.  I think that there is simple condition
which guarantees that nothing Spectre-related affects given
processor: the sequence of microarchitecutral operations (incuding
speculative operations) should depend only on architecturaly
executed instructions.
The easiest way to state this succinctly is::
No microarchitectural state can be updated until the instruction
causing said update retires. Caches, TLBs, and all predictor
state(s) has to be included in the above.

                        So, processor may do widely speculative
things, but only base speculation on architecturaly executed
instructions.
The processor can maintain look-ahead predictor state and use it
at decode/issue but it has to verify said state in order to retire.

               Some people try to just close single hole at
a time, IMO it is hopeless, there are too many possible
variations.
So far its been almost t10 years of closing one hole after another
and they are still closing holes. So, I agree with the hopeless-
ness of that line of attack.

             And weaker conditions, like "cancelling" effects
of speculative instructions are likely to fail.
These also lead to replay-storms.

Date Sujet#  Auteur
23 Oct 24 * Reverse engineering of Intel branch predictors34Thomas Koenig
23 Oct 24 +* Re: Reverse engineering of Intel branch predictors24MitchAlsup1
28 Oct 24 i`* Re: Reverse engineering of Intel branch predictors23Stefan Monnier
5 Nov 24 i `* Re: Reverse engineering of Intel branch predictors22MitchAlsup1
11 Nov 24 i  +* Re: Reverse engineering of Intel branch predictors2Thomas Koenig
11 Nov 24 i  i`- Re: Reverse engineering of Intel branch predictors1MitchAlsup1
11 Nov 24 i  `* Re: Reverse engineering of Intel branch predictors19Stefan Monnier
11 Nov 24 i   `* Re: Reverse engineering of Intel branch predictors18MitchAlsup1
12 Nov 24 i    `* Re: Reverse engineering of Intel branch predictors17Stefan Monnier
12 Nov 24 i     `* Re: Reverse engineering of Intel branch predictors16MitchAlsup1
12 Nov 24 i      +* Re: Reverse engineering of Intel branch predictors13Stefan Monnier
12 Nov 24 i      i`* Re: Reverse engineering of Intel branch predictors12MitchAlsup1
13 Nov 24 i      i +* Re: Reverse engineering of Intel branch predictors7Stefan Monnier
13 Nov 24 i      i i`* Re: Reverse engineering of Intel branch predictors6Terje Mathisen
13 Nov 24 i      i i `* Re: Reverse engineering of Intel branch predictors5Stefan Monnier
13 Nov 24 i      i i  `* Re: Reverse engineering of Intel branch predictors4Thomas Koenig
13 Nov 24 i      i i   +* Re: Reverse engineering of Intel branch predictors2Stefan Monnier
14 Nov 24 i      i i   i`- Re: Reverse engineering of Intel branch predictors1Thomas Koenig
14 Nov 24 i      i i   `- Interpreters and indirect-branch prediction (was: Reverse ...)1Anton Ertl
13 Nov 24 i      i `* Interpreters and indirect-branch prediction4Anton Ertl
13 Nov 24 i      i  `* Re: Interpreters and indirect-branch prediction3MitchAlsup1
13 Nov 24 i      i   `* Re: Interpreters and indirect-branch prediction2BGB
14 Nov 24 i      i    `- Re: Interpreters and indirect-branch prediction1BGB
13 Nov 24 i      `* Re: Reverse engineering of Intel branch predictors2Brett
13 Nov 24 i       `- Re: Reverse engineering of Intel branch predictors1MitchAlsup1
1 Nov 24 `* Re: Reverse engineering of Intel branch predictors9Waldek Hebisch
1 Nov 24  +- Re: Reverse engineering of Intel branch predictors1MitchAlsup1
5 Nov 24  `* Re: Reverse engineering of Intel branch predictors7Stefan Monnier
5 Nov 24   +- Re: Reverse engineering of Intel branch predictors1MitchAlsup1
8 Nov 24   `* Re: Reverse engineering of Intel branch predictors5Waldek Hebisch
8 Nov 24    +* Re: Reverse engineering of Intel branch predictors3MitchAlsup1
10 Nov 24    i`* Re: Reverse engineering of Intel branch predictors2Waldek Hebisch
10 Nov 24    i `- Re: Reverse engineering of Intel branch predictors1MitchAlsup1
11 Nov 24    `- Re: Reverse engineering of Intel branch predictors1Stefan Monnier

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