[llvm] r347617 - [clang][slh] add attribute for speculative load hardening

[Zola Bridges via llvm-commits]

Author: zbrid
Date: Mon Nov 26 16:03:44 2018
New Revision: 347617

URL: http://llvm.org/viewvc/llvm-project?rev=347617&view=rev
Log:
[clang][slh] add attribute for speculative load hardening

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

----- Summary from Previous Diff (Still Accurate) -----

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

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=347617&r1=347616&r2=347617&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Mon Nov 26 16:03:44 2018
@@ -1643,19 +1643,15 @@ example:
 ``speculative_load_hardening``
     This attribute indicates that
     `Speculative Load Hardening <https://llvm.org/docs/SpeculativeLoadHardening.html>`_
-    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.
+    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.
 
     When inlining, the attribute is sticky. Inlining a function that carries
     this attribute will cause the caller to gain the attribute. This is intended