[compiler-rt] [scudo] Add primary option to zero block on dealloc. (PR #142394)

[via llvm-commits]

https://github.com/piwicode created https://github.com/llvm/llvm-project/pull/142394

When all the blocks of a page are unused, the page will be full of zero and decommitted on operating systems that scan the memory.

Change-Id: I278055d82057090b0a04d812b49cf93fdf467478

>From 7b140733b4f317db535bcbaac70a5ed7da00102f Mon Sep 17 00:00:00 2001
From: Pierre Labatut <plabatut at google.com>
Date: Mon, 2 Jun 2025 15:19:02 +0200
Subject: [PATCH] [scudo] Add primary option to zero block on dealloc.

When all the blocks of a page are unused, the page will be full of zero
and decommitted on operating systems that scan the memory.

Change-Id: I278055d82057090b0a04d812b49cf93fdf467478
---
 .../lib/scudo/standalone/allocator_config.def |  5 ++++
 compiler-rt/lib/scudo/standalone/primary64.h  |  1 +
 .../scudo/standalone/size_class_allocator.h   |  9 +++++++
 .../scudo/standalone/tests/primary_test.cpp   | 24 ++++++++++++++++++-
 4 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/compiler-rt/lib/scudo/standalone/allocator_config.def b/compiler-rt/lib/scudo/standalone/allocator_config.def
index 84fcec0877d40..2d58cb0a4d392 100644
--- a/compiler-rt/lib/scudo/standalone/allocator_config.def
+++ b/compiler-rt/lib/scudo/standalone/allocator_config.def
@@ -111,6 +111,11 @@ PRIMARY_OPTIONAL_TYPE(ConditionVariableT, ConditionVariableDummy)
 // to, in increments of a power-of-2 scale. See `CompactPtrScale` also.
 PRIMARY_OPTIONAL_TYPE(CompactPtrT, uptr)
 
+// Clears the memory slot when a allocation is returned to the allocator.
+// Operating systems that detects pages filled with zeroes will decommit
+// memory.
+PRIMARY_OPTIONAL(const bool, ZeroOnDealloc, false)
+
 // SECONDARY_REQUIRED_TEMPLATE_TYPE(NAME)
 //
 // Defines the type of Secondary Cache to use.
diff --git a/compiler-rt/lib/scudo/standalone/primary64.h b/compiler-rt/lib/scudo/standalone/primary64.h
index 25ee999199114..145ee26dd855f 100644
--- a/compiler-rt/lib/scudo/standalone/primary64.h
+++ b/compiler-rt/lib/scudo/standalone/primary64.h
@@ -53,6 +53,7 @@ template <typename Config> class SizeClassAllocator64 {
   static const uptr CompactPtrScale = Config::getCompactPtrScale();
   static const uptr RegionSizeLog = Config::getRegionSizeLog();
   static const uptr GroupSizeLog = Config::getGroupSizeLog();
+  static const bool ZeroOnDealloc = Config::getZeroOnDealloc();
   static_assert(RegionSizeLog >= GroupSizeLog,
                 "Group size shouldn't be greater than the region size");
   static const uptr GroupScale = GroupSizeLog - CompactPtrScale;
diff --git a/compiler-rt/lib/scudo/standalone/size_class_allocator.h b/compiler-rt/lib/scudo/standalone/size_class_allocator.h
index 7c7d6307f8f0a..219b08774bcb6 100644
--- a/compiler-rt/lib/scudo/standalone/size_class_allocator.h
+++ b/compiler-rt/lib/scudo/standalone/size_class_allocator.h
@@ -59,6 +59,11 @@ template <class SizeClassAllocator> struct SizeClassAllocatorLocalCache {
 
   bool deallocate(uptr ClassId, void *P) {
     CHECK_LT(ClassId, NumClasses);
+
+    if(SizeClassAllocator::ZeroOnDealloc) {
+      memset(P, 0, SizeClassAllocator::getSizeByClassId(ClassId));
+    }
+
     PerClass *C = &PerClassArray[ClassId];
 
     // If the cache is full, drain half of blocks back to the main allocator.
@@ -211,6 +216,10 @@ template <class SizeClassAllocator> struct SizeClassAllocatorNoCache {
   bool deallocate(uptr ClassId, void *P) {
     CHECK_LT(ClassId, NumClasses);
 
+    if(SizeClassAllocator::ZeroOnDealloc) {
+      memset(P, 0, SizeClassAllocator::getSizeByClassId(ClassId));
+    }
+
     if (ClassId == BatchClassId)
       return deallocateBatchClassBlock(P);
 
diff --git a/compiler-rt/lib/scudo/standalone/tests/primary_test.cpp b/compiler-rt/lib/scudo/standalone/tests/primary_test.cpp
index 7dc38c2ede8ca..47bfc3a9fc242 100644
--- a/compiler-rt/lib/scudo/standalone/tests/primary_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/primary_test.cpp
@@ -150,6 +150,27 @@ template <typename SizeClassMapT> struct TestConfig5 {
   };
 };
 
+// Enable `ZeroOnDealloc`
+template <typename SizeClassMapT> struct TestConfig6 {
+  static const bool MaySupportMemoryTagging = false;
+  template <typename> using TSDRegistryT = void;
+  template <typename> using PrimaryT = void;
+  template <typename> using SecondaryT = void;
+
+  struct Primary {
+    using SizeClassMap = SizeClassMapT;
+    static const scudo::uptr RegionSizeLog = 18U;
+    static const scudo::uptr GroupSizeLog = 18U;
+    static const scudo::s32 MinReleaseToOsIntervalMs = INT32_MIN;
+    static const scudo::s32 MaxReleaseToOsIntervalMs = INT32_MAX;
+    typedef scudo::uptr CompactPtrT;
+    static const scudo::uptr CompactPtrScale = 0;
+    static const bool EnableRandomOffset = true;
+    static const scudo::uptr MapSizeIncrement = 1UL << 18;
+    static const bool ZeroOnDealloc = true;
+  };
+};
+
 template <template <typename> class BaseConfig, typename SizeClassMapT>
 struct Config : public BaseConfig<SizeClassMapT> {};
 
@@ -191,7 +212,8 @@ struct ScudoPrimaryTest : public Test {};
   SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TestConfig2)                            \
   SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TestConfig3)                            \
   SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TestConfig4)                            \
-  SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TestConfig5)
+  SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TestConfig5)                            \
+  SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TestConfig6)
 #endif
 
 #define SCUDO_TYPED_TEST_TYPE(FIXTURE, NAME, TYPE)                             \