| commit | 92b7c89e6e8ba82924b57153bea68241cc45f658 | [log] [tgz] |
|---|---|---|
| author | David Benjamin <davidben@google.com> | Mon Jun 17 20:26:24 2019 +0000 |
| committer | Adam Langley <agl@google.com> | Wed Jun 19 17:19:13 2019 +0000 |
| tree | dfb07ffb2849bec2e5866c3afd26313ed74a9b14 | |
| parent | 12d9ed670da3edd64ce8175cfe0e091982989c18 [diff] |
Add a value barrier to constant-time selects. Clang recognizes the (mask & a) | (~mask & b) pattern as a select. While it often optimizes this into a cmov, it sometimes inserts branches instead, particularly when it detects a string of cmovs with the same condition. In the long term, we need language-level support for expressing our constraints. In the short term, introduce value barriers to prevent the compiler from reasoning about our bit tricks. Thanks to Chandler Carruth for suggesting this pattern. It should be reasonably robust, short of value-based PGO or the compiler learning to reason about empty inline assembly blocks. Apply barriers to our various constant-time selects. We should invest more in the valgrind-based tooling to figure out if there are other instances. Change-Id: Icc24ce36a61f7fec021a762c27197b9c5bd28c5d Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/36484 Reviewed-by: Chandler Carruth <chandlerc@google.com> Reviewed-by: Adam Langley <agl@google.com>
BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.
Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.
Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.
BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.
Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.
There are other files in this directory which might be helpful: