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89d51d5f29
Because this exploit has been widely known for years and has not been fixed by Mojang, we decided that it was worth allowing people to toggle it on/off due to how easy it is to make it configurable. It should be noted that this decision does not promise all future exploits will be configurable.
58 lines
3.3 KiB
Diff
58 lines
3.3 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: stonar96 <minecraft.stonar96@gmail.com>
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Date: Sun, 17 Jan 2021 01:11:36 +0100
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Subject: [PATCH] Optimize HashMapPalette
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HashMapPalette uses an instance of CrudeIncrementalIntIdentityHashBiMap
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internally. A Palette has a preset maximum size = 1 << bits.
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CrudeIncrementalIntIdentityHashBiMap has an initial size but is
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automatically resized. The CrudeIncrementalIntIdentityHashBiMap is created
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with the maximum size in the constructor of HashMapPalette, with the aim
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that it doesn't need to be resized anymore. However, there are two things
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that I think Mojang hasn't considered here:
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1) The CrudeIncrementalIntIdentityHashBiMap is resized, when its initial
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size is reached and not the next time, when a further object is added.
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2) HashMapPalette adds objects (unnecessarily) before checking if the
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initial size of CrudeIncrementalIntIdentityHashBiMap is reached.
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This means to actually avoid resize operations in
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CrudeIncrementalIntIdentityHashBiMap, one has to add 2 to the initial size
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or add 1 and check the size before adding objects. This commit implements
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the second approach. Note that this isn't only an optimization but also
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makes async reads of Palettes fail-safe. An async read while the
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CrudeIncrementalIntIdentityHashBiMap is resized is fatal and can even lead
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to corrupted data. This is also something that Anti-Xray is currently
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relying on.
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diff --git a/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java b/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java
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index 26e093243c70313b777483d9555fb1557443c9b8..92c360f02ef6be77c6c8eee3226947468194ec23 100644
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--- a/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java
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+++ b/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java
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@@ -20,7 +20,7 @@ public class HashMapPalette<T> implements Palette<T> {
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}
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public HashMapPalette(IdMap<T> idList, int indexBits, PaletteResize<T> listener) {
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- this(idList, indexBits, listener, CrudeIncrementalIntIdentityHashBiMap.create(1 << indexBits));
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+ this(idList, indexBits, listener, CrudeIncrementalIntIdentityHashBiMap.create((1 << indexBits) + 1)); // Paper - Perf: Avoid unnecessary resize operation in CrudeIncrementalIntIdentityHashBiMap
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}
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private HashMapPalette(IdMap<T> idList, int indexBits, PaletteResize<T> listener, CrudeIncrementalIntIdentityHashBiMap<T> map) {
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@@ -38,10 +38,16 @@ public class HashMapPalette<T> implements Palette<T> {
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public int idFor(T object) {
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int i = this.values.getId(object);
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if (i == -1) {
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- i = this.values.add(object);
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- if (i >= 1 << this.bits) {
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+ // Paper start - Perf: Avoid unnecessary resize operation in CrudeIncrementalIntIdentityHashBiMap and optimize
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+ // We use size() instead of the result from add(K)
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+ // This avoids adding another object unnecessarily
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+ // Without this change, + 2 would be required in the constructor
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+ if (this.values.size() >= 1 << this.bits) {
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i = this.resizeHandler.onResize(this.bits + 1, object);
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+ } else {
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+ i = this.values.add(object);
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}
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+ // Paper end - Perf: Avoid unnecessary resize operation in CrudeIncrementalIntIdentityHashBiMap and optimize
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}
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return i;
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