tree 0aa3c324148f930bca7e41ec1d55d06b5bd84cea
parent bcda68447b31b86bc3829fca80454ca1a2a572e0
author Joel Sing <joel@sing.id.au> 1589904837 +1000
committer Joel Sing <joel@sing.id.au> 1590512566 +0000

runtime, syscall: correct openbsd/arm and openbsd/arm64 syscalls for OpenBSD 6.7

Add two no op instructions following svc on openbsd/arm64 and swi on openbsd/arm.

All except some of the most recent arm64 processors have a speculative execution
flaw that occurs across a syscall boundary, which cannot be mitigated in the
kernel. In order to protect against this leak a speculation barrier needs to be
placed after an svc or swi instruction.

In order to avoid the performance impact of these instructions, the OpenBSD 6.7
kernel returns execution two instructions past the svc or swi call. For now two
hardware no ops are added, which allows syscalls to work with both 6.6 and 6.7.
These should be replaced with real speculation barriers once OpenBSD 6.8 is
released.

Updates #36435

Change-Id: I06153cb0998199242cca8761450e53599c3e7de4
Reviewed-on: https://go-review.googlesource.com/c/go/+/234381
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>