[llvm] r347628 - Revert "[clang][slh] add attribute for speculative load hardening"

[Zola Bridges via llvm-commits]

Author: zbrid
Date: Mon Nov 26 18:22:00 2018
New Revision: 347628

URL: http://llvm.org/viewvc/llvm-project?rev=347628&view=rev
Log:
Revert "[clang][slh] add attribute for speculative load hardening"

until I figure out why the build is failing or timing out

***************************

Summary:
The prior diff had to be reverted because there were two tests
that failed. I updated the two tests in this diff

clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/SemaCXX/attr-speculative-load-hardening.cpp

LLVM IR already has an attribute for speculative_load_hardening. Before
this commit, when a user passed the -mspeculative-load-hardening flag to
Clang, every function would have this attribute added to it. This Clang
attribute will allow users to opt into SLH on a function by function
basis.

This can be applied to functions and Objective C methods.

Reviewers: chandlerc, echristo, kristof.beyls, aaron.ballman

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54915

This reverts commit a5b3c232d1e3613f23efbc3960f8e23ea70f2a79.
(r347617)

Modified:
    llvm/trunk/docs/LangRef.rst

Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=347628&r1=347627&r2=347628&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Mon Nov 26 18:22:00 2018
@@ -1643,15 +1643,19 @@ example:
 ``speculative_load_hardening``
     This attribute indicates that
     `Speculative Load Hardening <https://llvm.org/docs/SpeculativeLoadHardening.html>`_
-    should be enabled for the function body.
-
-    Speculative Load Hardening is a best-effort mitigation against
-    information leak attacks that make use of control flow
-    miss-speculation - specifically miss-speculation of whether a branch
-    is taken or not. Typically vulnerabilities enabling such attacks are
-    classified as "Spectre variant #1". Notably, this does not attempt to
-    mitigate against miss-speculation of branch target, classified as
-    "Spectre variant #2" vulnerabilities.
+    should be enabled for the function body. This is a best-effort attempt to
+    mitigate all known speculative execution information leak vulnerabilities
+    that are based on the fundamental principles of modern processors'
+    speculative execution. These vulnerabilities are classified as "Spectre
+    variant #1" vulnerabilities typically. Notably, this does not attempt to
+    mitigate any vulnerabilities where the speculative execution and/or
+    prediction devices of specific processors can be *completely* undermined
+    (such as "Branch Target Injection", a.k.a, "Spectre variant #2"). Instead,
+    this is a target-independent request to harden against the completely
+    generic risk posed by speculative execution to incorrectly load secret data,
+    making it available to some micro-architectural side-channel for information
+    leak. For a processor without any speculative execution or predictors, this
+    is expected to be a no-op.
 
     When inlining, the attribute is sticky. Inlining a function that carries
     this attribute will cause the caller to gain the attribute. This is intended