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[scudo] Apply filling option when realloc grows a block in-place too #93212

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Merged
merged 3 commits into from
Jun 10, 2024
Merged

[scudo] Apply filling option when realloc grows a block in-place too #93212

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1e55c81
[scudo] Apply filling option when realloc grows a block in-place too
fabio-d May 23, 2024
17625ca
Moved test to ScudoCombinedDeathTest::ReallocateSame
fabio-d Jun 4, 2024
4826711
Apply fill when shrank instead of when grown
fabio-d Jun 5, 2024
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13 changes: 13 additions & 0 deletions compiler-rt/lib/scudo/standalone/combined.h
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Original file line number Diff line number Diff line change
Expand Up @@ -565,6 +565,19 @@ class Allocator {
storeSecondaryAllocationStackMaybe(Options, OldPtr, NewSize);
}
}

// If we've increased the size, fill the extra bytes.
if (NewSize > OldSize) {
const FillContentsMode FillContents =
TSDRegistry.getDisableMemInit() ? NoFill
: Options.getFillContentsMode();
if (FillContents != NoFill) {
memset(reinterpret_cast<char *>(OldTaggedPtr) + OldSize,
FillContents == ZeroFill ? 0 : PatternFillByte,
NewSize - OldSize);
}
}

return OldTaggedPtr;
}
}
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21 changes: 21 additions & 0 deletions compiler-rt/lib/scudo/standalone/tests/combined_test.cpp
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Expand Up @@ -347,7 +347,17 @@ SCUDO_TYPED_TEST(ScudoCombinedTest, ZeroFill) {
EXPECT_NE(P, nullptr);
for (scudo::uptr I = 0; I < Size; I++)
ASSERT_EQ((reinterpret_cast<char *>(P))[I], '\0');

// Fill with a non-zero pattern.
memset(P, 0xaa, Size);

// Shrink and then grow by one byte, verifying that it gets re-filled in
// the process. We assume that changing the size by just 1 is done in
// place.
ASSERT_EQ(Allocator->reallocate(P, Size - 1), P);
ASSERT_EQ(Allocator->reallocate(P, Size), P);
EXPECT_EQ((reinterpret_cast<unsigned char *>(P))[Size - 1], '\0');

Allocator->deallocate(P, Origin, Size);
}
}
Expand All @@ -374,7 +384,18 @@ SCUDO_TYPED_TEST(ScudoCombinedTest, PatternOrZeroFill) {
else
ASSERT_TRUE(V == scudo::PatternFillByte || V == 0);
}

// Fill with a known pattern different from PatternFillByte.
memset(P, 0xaa, Size);

// Shrink and then grow by one byte, verifying that it gets re-filled in
// the process. We assume that changing the size by just 1 is done in
// place.
ASSERT_EQ(Allocator->reallocate(P, Size - 1), P);
ASSERT_EQ(Allocator->reallocate(P, Size), P);
EXPECT_EQ((reinterpret_cast<unsigned char *>(P))[Size - 1],
scudo::PatternFillByte);

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I think we shouldn't make the assumption that "changing the size by just 1 is done in place" in the test.

Given that this has no immediate impact and is not harmful if we don't test it. I think it's fine to leave it untested.

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If you really want to test this, I would suggest having a dedicated config to ensure that the shrinking and expending use the same block

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I'm seeing that there's already a similar assumption in ScudoCombinedDeathTest::ReallocateSame, so another possibility could maybe be to extend that test instead of having to maintain a new config. What about this?

 SCUDO_TYPED_TEST(ScudoCombinedDeathTest, ReallocateSame) {
   auto *Allocator = this->Allocator.get();
 
   // Check that reallocating a chunk to a slightly smaller or larger size
   // returns the same chunk. This requires that all the sizes we iterate on use
   // the same block size, but that should be the case for MaxSize - 64 with our
   // default class size maps.
   constexpr scudo::uptr ReallocSize =
       TypeParam::Primary::SizeClassMap::MaxSize - 64;
   void *P = Allocator->allocate(ReallocSize, Origin);
   const char Marker = 'A';
   memset(P, Marker, ReallocSize);
+  Allocator->setFillContents(scudo::PatternOrZeroFill);
   for (scudo::sptr Delta = -32; Delta < 32; Delta += 8) {
     const scudo::uptr NewSize =
         static_cast<scudo::uptr>(static_cast<scudo::sptr>(ReallocSize) + Delta);
     void *NewP = Allocator->reallocate(P, NewSize);
     EXPECT_EQ(NewP, P);

+    // Verify that existing contents have been preserved.
     for (scudo::uptr I = 0; I < ReallocSize - 32; I++)
       EXPECT_EQ((reinterpret_cast<char *>(NewP))[I], Marker);
+
+    // Verify that, if we have grown the allocation, new bytes have been set
+    // according to FillContentsMode.
+    for (scudo::uptr I = ReallocSize - 32; I < NewSize; I++)
+      EXPECT_EQ((reinterpret_cast<unsigned char *>(NewP))[I],
+                scudo::PatternFillByte);

     checkMemoryTaggingMaybe(Allocator, NewP, NewSize, 0);
   }
   Allocator->deallocate(P, Origin);
 }

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Right, I think we can utilize this test. BTW, it seems to me that the test has some problem. ReallocSize - 32 only checks the constant range of memory with marker filled. We may want to do it like,

for (scudo::sptr Delta = -32; Delta < 32; Delta += 8) {
  // 1. memset(P, Marker, CurrentSize);
  // 2. Calculate NewSize and do the realloc
  // 3. Check the content needed to be preserved
  // 4. Check the in-place growing does fill the extended bytes
  }

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Thanks! I've modified the test accordingly, LMK

Allocator->deallocate(P, Origin, Size);
}
}
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