release/22.x: [LLD][COFF] Fix out-of-bounds write when filling gaps with INT3 in code sections (#180411) - #198212
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release/22.x: [LLD][COFF] Fix out-of-bounds write when filling gaps with INT3 in code sections (#180411)#198212llvmbot wants to merge 1 commit into
llvmbot wants to merge 1 commit into
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…de sections (llvm#180411) When merging `.bss` into a code section (e.g., `/MERGE:.bss=.text`), the INT3 gap-filling loop in `writeSections()` would write past the output buffer. This happens because `.bss` chunks have `hasData=false`, so they contribute to `VirtualSize` but not `SizeOfRawData`. The loop was using chunk RVAs without checking if they exceeded the raw data region. This caused a crash on Windows with `/FILEALIGN:1` (access violation 0xC0000005). The tight alignment leaves no slack in the mapped buffer, so the overflow immediately hits unmapped memory. The fix bounds all memset operations to `rawSize` and exits early when encountering chunks beyond the raw data boundary. Fixes llvm#180406 (cherry picked from commit 6558595)
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@aganea What do you think about merging this PR to the release branch? |
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@llvm/pr-subscribers-platform-windows @llvm/pr-subscribers-lld-coff Author: llvmbot ChangesBackport 6558595 Requested by: @mstorsjo Full diff: https://github.com/llvm/llvm-project/pull/198212.diff 2 Files Affected:
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 3ac26681541ba..4451cfeb3dd63 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -2617,12 +2617,17 @@ void Writer::writeSections() {
if ((sec->header.Characteristics & IMAGE_SCN_CNT_CODE) &&
(ctx.config.machine == AMD64 || ctx.config.machine == I386)) {
uint32_t prevEnd = 0;
+ uint32_t rawSize = sec->getRawSize();
for (Chunk *c : sec->chunks) {
uint32_t off = c->getRVA() - sec->getRVA();
+ // Chunks without data (e.g., .bss) have virtual addresses beyond
+ // rawSize; stop filling when we reach the end of raw data.
+ if (off >= rawSize)
+ break;
memset(secBuf + prevEnd, 0xCC, off - prevEnd);
- prevEnd = off + c->getSize();
+ prevEnd = std::min(off + static_cast<uint32_t>(c->getSize()), rawSize);
}
- memset(secBuf + prevEnd, 0xCC, sec->getRawSize() - prevEnd);
+ memset(secBuf + prevEnd, 0xCC, rawSize - prevEnd);
}
parallelForEach(sec->chunks, [&](Chunk *c) {
diff --git a/lld/test/COFF/merge-bss-text-filealign1.test b/lld/test/COFF/merge-bss-text-filealign1.test
new file mode 100644
index 0000000000000..4b03a11fae16b
--- /dev/null
+++ b/lld/test/COFF/merge-bss-text-filealign1.test
@@ -0,0 +1,60 @@
+# REQUIRES: x86
+# Test that merging .bss into .text with /FILEALIGN:1 doesn't crash.
+#
+# RUN: yaml2obj %s -o %t.obj
+# RUN: lld-link /out:%t.exe /entry:main /subsystem:console \
+# RUN: /merge:.bss=.text /filealign:1 %t.obj
+# RUN: llvm-readobj --sections %t.exe | FileCheck %s
+
+# CHECK: Name: .text
+# CHECK-NEXT: VirtualSize: 0x104
+# CHECK: RawDataSize:
+# CHECK-NOT: Name: .bss
+
+--- !COFF
+header:
+ Machine: IMAGE_FILE_MACHINE_AMD64
+ Characteristics: [ ]
+sections:
+ - Name: .text
+ Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+ Alignment: 4
+ SectionData: 'C3'
+ SizeOfRawData: 1
+ - Name: .bss
+ Characteristics: [ IMAGE_SCN_CNT_UNINITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+ Alignment: 4
+ SectionData: ''
+ SizeOfRawData: 256
+symbols:
+ - Name: .text
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ SectionDefinition:
+ Length: 1
+ NumberOfRelocations: 0
+ NumberOfLinenumbers: 0
+ CheckSum: 0
+ Number: 1
+ - Name: .bss
+ Value: 0
+ SectionNumber: 2
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ SectionDefinition:
+ Length: 256
+ NumberOfRelocations: 0
+ NumberOfLinenumbers: 0
+ CheckSum: 0
+ Number: 2
+ - Name: main
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+...
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@llvm/pr-subscribers-lld Author: llvmbot ChangesBackport 6558595 Requested by: @mstorsjo Full diff: https://github.com/llvm/llvm-project/pull/198212.diff 2 Files Affected:
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 3ac26681541ba..4451cfeb3dd63 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -2617,12 +2617,17 @@ void Writer::writeSections() {
if ((sec->header.Characteristics & IMAGE_SCN_CNT_CODE) &&
(ctx.config.machine == AMD64 || ctx.config.machine == I386)) {
uint32_t prevEnd = 0;
+ uint32_t rawSize = sec->getRawSize();
for (Chunk *c : sec->chunks) {
uint32_t off = c->getRVA() - sec->getRVA();
+ // Chunks without data (e.g., .bss) have virtual addresses beyond
+ // rawSize; stop filling when we reach the end of raw data.
+ if (off >= rawSize)
+ break;
memset(secBuf + prevEnd, 0xCC, off - prevEnd);
- prevEnd = off + c->getSize();
+ prevEnd = std::min(off + static_cast<uint32_t>(c->getSize()), rawSize);
}
- memset(secBuf + prevEnd, 0xCC, sec->getRawSize() - prevEnd);
+ memset(secBuf + prevEnd, 0xCC, rawSize - prevEnd);
}
parallelForEach(sec->chunks, [&](Chunk *c) {
diff --git a/lld/test/COFF/merge-bss-text-filealign1.test b/lld/test/COFF/merge-bss-text-filealign1.test
new file mode 100644
index 0000000000000..4b03a11fae16b
--- /dev/null
+++ b/lld/test/COFF/merge-bss-text-filealign1.test
@@ -0,0 +1,60 @@
+# REQUIRES: x86
+# Test that merging .bss into .text with /FILEALIGN:1 doesn't crash.
+#
+# RUN: yaml2obj %s -o %t.obj
+# RUN: lld-link /out:%t.exe /entry:main /subsystem:console \
+# RUN: /merge:.bss=.text /filealign:1 %t.obj
+# RUN: llvm-readobj --sections %t.exe | FileCheck %s
+
+# CHECK: Name: .text
+# CHECK-NEXT: VirtualSize: 0x104
+# CHECK: RawDataSize:
+# CHECK-NOT: Name: .bss
+
+--- !COFF
+header:
+ Machine: IMAGE_FILE_MACHINE_AMD64
+ Characteristics: [ ]
+sections:
+ - Name: .text
+ Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+ Alignment: 4
+ SectionData: 'C3'
+ SizeOfRawData: 1
+ - Name: .bss
+ Characteristics: [ IMAGE_SCN_CNT_UNINITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+ Alignment: 4
+ SectionData: ''
+ SizeOfRawData: 256
+symbols:
+ - Name: .text
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ SectionDefinition:
+ Length: 1
+ NumberOfRelocations: 0
+ NumberOfLinenumbers: 0
+ CheckSum: 0
+ Number: 1
+ - Name: .bss
+ Value: 0
+ SectionNumber: 2
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ SectionDefinition:
+ Length: 256
+ NumberOfRelocations: 0
+ NumberOfLinenumbers: 0
+ CheckSum: 0
+ Number: 2
+ - Name: main
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+...
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Contributor
Member
Yeah I'm happy to backport this (I didn't approve it myself first since I was the one that requested it), but if @aganea is unavailable I'll press the button. |
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moved this from Needs Review
to Needs Merge
in LLVM Release Status
Member
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#180411 (comment) (Somehow GitHub has hidden it)
This might be a problem. |
Member
Thanks for pointing this out - I missed this comment. I'm not entirely convinced that the issue is caused by this commit though. But perhaps that's reason enough to hold back off backporting it after all? |
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Backport 6558595
Requested by: @mstorsjo