[scudo] Always zero on linux even if the memory cannot be released. #167788
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If a caller has locked memory, then the madvise call will fail. In that case, zero the memory so that we don't return non-zeroed memory for calloc calls since we thought the memory had been released.
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compiler-rt:scudo
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@llvm/pr-subscribers-compiler-rt-sanitizer Author: Christopher Ferris (cferris1000) ChangesIf a caller has locked memory, then the madvise call will fail. In that case, zero the memory so that we don't return non-zeroed memory for calloc calls since we thought the memory had been released. Full diff: https://github.com/llvm/llvm-project/pull/167788.diff 2 Files Affected:
diff --git a/compiler-rt/lib/scudo/standalone/mem_map_linux.cpp b/compiler-rt/lib/scudo/standalone/mem_map_linux.cpp
index 783c4f0d9ab0f..df3e54cab6695 100644
--- a/compiler-rt/lib/scudo/standalone/mem_map_linux.cpp
+++ b/compiler-rt/lib/scudo/standalone/mem_map_linux.cpp
@@ -122,7 +122,12 @@ void MemMapLinux::setMemoryPermissionImpl(uptr Addr, uptr Size, uptr Flags) {
void MemMapLinux::releaseAndZeroPagesToOSImpl(uptr From, uptr Size) {
void *Addr = reinterpret_cast<void *>(From);
- while (madvise(Addr, Size, MADV_DONTNEED) == -1 && errno == EAGAIN) {
+ int rc;
+ while ((rc = madvise(Addr, Size, MADV_DONTNEED)) == -1 && errno == EAGAIN) {
+ }
+ if (rc == -1) {
+ // If we can't madvies the memory, then we still need to zero it.
+ memset(Addr, 0, Size);
}
}
diff --git a/compiler-rt/lib/scudo/standalone/tests/map_test.cpp b/compiler-rt/lib/scudo/standalone/tests/map_test.cpp
index cc7d3ee4dc6c2..fadc0e00c7844 100644
--- a/compiler-rt/lib/scudo/standalone/tests/map_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/map_test.cpp
@@ -14,6 +14,10 @@
#include <string.h>
#include <unistd.h>
+#if SCUDO_LINUX
+#include <sys/mman.h>
+#endif
+
static const char *MappingName = "scudo:test";
TEST(ScudoMapTest, PageSize) {
@@ -89,3 +93,40 @@ TEST(ScudoMapTest, MapGrowUnmap) {
memset(reinterpret_cast<void *>(Q), 0xbb, PageSize);
MemMap.unmap();
}
+
+// Verify that zeroing works properly.
+TEST(ScudoMapTest, Zeroing) {
+ scudo::ReservedMemoryT ReservedMemory;
+ const scudo::uptr PageSize = scudo::getPageSizeCached();
+ const scudo::uptr Size = 3 * PageSize;
+ ReservedMemory.create(/*Addr=*/0U, Size, MappingName);
+ ASSERT_TRUE(ReservedMemory.isCreated());
+
+ scudo::MemMapT MemMap = ReservedMemory.dispatch(ReservedMemory.getBase(), ReservedMemory.getCapacity());
+ EXPECT_TRUE(MemMap.remap(MemMap.getBase(), MemMap.getCapacity(), MappingName));
+ unsigned char *Data = reinterpret_cast<unsigned char*>(MemMap.getBase());
+ memset(Data, 1U, MemMap.getCapacity());
+ // Spot check some values.
+ EXPECT_EQ(1U, Data[0]);
+ EXPECT_EQ(1U, Data[PageSize]);
+ EXPECT_EQ(1U, Data[PageSize * 2]);
+ MemMap.releaseAndZeroPagesToOS(MemMap.getBase(), MemMap.getCapacity());
+ EXPECT_EQ(0U, Data[0]);
+ EXPECT_EQ(0U, Data[PageSize]);
+ EXPECT_EQ(0U, Data[PageSize * 2]);
+
+#if SCUDO_LINUX
+ // Now verify that if madvise fails, the data is still zeroed.
+ memset(Data, 1U, MemMap.getCapacity());
+ EXPECT_NE(-1, mlock(Data, MemMap.getCapacity()));
+ EXPECT_EQ(1U, Data[0]);
+ EXPECT_EQ(1U, Data[PageSize]);
+ EXPECT_EQ(1U, Data[PageSize * 2]);
+ MemMap.releaseAndZeroPagesToOS(MemMap.getBase(), MemMap.getCapacity());
+ EXPECT_EQ(0U, Data[0]);
+ EXPECT_EQ(0U, Data[PageSize]);
+ EXPECT_EQ(0U, Data[PageSize * 2]);
+#endif
+
+ MemMap.unmap();
+}
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✅ With the latest revision this PR passed the C/C++ code formatter. |
ChiaHungDuan
approved these changes
Nov 13, 2025
Comment on lines
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| if (rc == -1) { | ||
| // If we can't madvies the memory, then we still need to zero it. | ||
| memset(Addr, 0, Size); |
Contributor
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I was thinking if we want to check something like "errno == EPERM". It seems not making any difference to the problem but maybe it helps with some other cases. I guess not...
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Author
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Yeah, when I checked this the errno was EINVAL, which is not what I was expecting. It seems safer to just memset when it fails for whatever reason.
Member
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The new test is failing for me while testing on Gentoo/arm64: This is on top of d9dfe75. Neoverse-N1. glibc 2.41. |
Contributor
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The new test also fails on ppc64le starting with https://lab.llvm.org/buildbot/#/builders/145/builds/10835 |
Contributor
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@cferris1000 Do you mind having a look at the ppc64le failures, possibly reverting until you can investigate further? |
Contributor
Author
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This looks like mlock/munlock are not supported everywhere, so I'll fix the test right now. |
Contributor
Author
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I believe this should pull request should fix this: |
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If a caller has locked memory, then the madvise call will fail. In that case, zero the memory so that we don't return non-zeroed memory for calloc calls since we thought the memory had been released.