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Mitigate Spectre by reducing the resolution of performance.now() to 20
microseconds. Based on:
https://hg.mozilla.org/releases/mozilla-release/rev/afa87f9be3a8
For more details, see:
https://blog.mozilla.org/security/2018/01/03/mitigations-landing-new-class-timing-attack/
This patch was modified to apply cleanly to GNU IceCat.
# HG changeset patch
# User Tom Ritter <tom@mozilla.com>
# Date 1514660820 21600
# Node ID afa87f9be3a8852da3a30f286b15ae599c7874f6
# Parent 6caa457ebedc915b43dc1d054b8fe22e82ca7447
Bug 1427870 - Change resolution of .now() to 20us. r=bkelly, a=lizzard
The comment about workers was introduced in Bug 1186489 but became obsolete some time after that
(definitely by Bug 1278838)
diff --git a/dom/performance/Performance.cpp b/dom/performance/Performance.cpp
--- a/dom/performance/Performance.cpp
+++ b/dom/performance/Performance.cpp
@@ -234,20 +234,19 @@ Performance::ClearResourceTimings()
{
MOZ_ASSERT(NS_IsMainThread());
mResourceEntries.Clear();
}
DOMHighResTimeStamp
Performance::RoundTime(double aTime) const
{
- // Round down to the nearest 5us, because if the timer is too accurate people
- // can do nasty timing attacks with it. See similar code in the worker
- // Performance implementation.
- const double maxResolutionMs = 0.005;
+ // Round down to the nearest 20us, because if the timer is too accurate people
+ // can do nasty timing attacks with it.
+ const double maxResolutionMs = 0.020;
return floor(aTime / maxResolutionMs) * maxResolutionMs;
}
void
Performance::Mark(const nsAString& aName, ErrorResult& aRv)
{
// Don't add the entry if the buffer is full. XXX should be removed by bug 1159003.
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