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[llvm-objcopy][ELF] --only-keep-debug: set offset/size of segments with no sections to zero 

PR50160: we currently ignore non-PT_PHDR segments with no sections, not
accounting for its p_offset and p_filesz: this can cause an out-of-bounds write
in `writeSegmentData` if the p_offset+p_filesz is larger than the total file
size.

This can be fixed by setting p_offset=p_filesz=0. The logic nicely unifies with
the logic added in D90897.

Reviewed By: jhenderson, rupprecht

Differential Revision: https://reviews.llvm.org/D101560
This commit is contained in:
Fangrui Song 2021-05-05 10:26:57 -07:00
parent ba5c122647
commit b3336bfa2e
2 changed files with 51 additions and 12 deletions
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42
llvm/test/tools/llvm-objcopy/ELF/only-keep-debug.test
View File

@ -129,11 +129,11 @@ ProgramHeaders:
# CHECK2-NEXT: [ 4] .strtab STRTAB 0000000000000000 000221 000001 00 0 0 1
# CHECK2-NEXT: [ 5] .shstrtab STRTAB 0000000000000000 000222 00002b 00 0 0 1
## Check that p_offset or p_filesz of empty segments or PT_PHDR are not modified.
## Check that p_offset or p_filesz of PT_PHDR are not modified.
# CHECK2: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
# CHECK2-NEXT: PHDR 0x000040 0x0000000000000040 0x0000000000000040 0x0000a8 0x0000a8 R 0x8
# CHECK2-NEXT: LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x000202 0x000202 R E 0x1000
# CHECK2-NEXT: LOAD 0x000202 0x0000000000000202 0x0000000000000202 0x00000e 0x00000e RW 0x1
# CHECK2-NEXT: LOAD 0x000000 0x0000000000000202 0x0000000000000202 0x000000 0x00000e RW 0x1
--- !ELF
FileHeader:
@ -280,3 +280,41 @@ ProgramHeaders:
VAddr: 0x1240
FirstSec: .tdata
LastSec: .tdata
## The offset and size fields of segments which contain no section and have no
## parent segment are set to zeros, so that we can decrease the file size. Such
## segments are not useful for debugging.
# RUN: yaml2obj --docnum=5 %s -o %t5
# RUN: llvm-objcopy --only-keep-debug %t5 %t5.dbg
# RUN: llvm-readelf -S -l %t5.dbg | FileCheck --check-prefix=CHECK5 %s
# RUN: llvm-objcopy --strip-sections %t5 %t5s
# RUN: llvm-objcopy --only-keep-debug %t5s %t5s.dbg
# RUN: llvm-readelf -S -l %t5s.dbg | FileCheck --check-prefix=CHECK5S %s
# CHECK5: [Nr] Name Type Address Off Size ES Flg Lk Inf Al
# CHECK5: [ 1] .foo NOBITS 0000000000000000 000078 001000 00 A 0 0 0
# CHECK5-NEXT: [ 2] .strtab STRTAB 0000000000000000 000078 000001 00 0 0 1
# CHECK5-NEXT: [ 3] .shstrtab STRTAB 0000000000000000 000079 000018 00 0 0 1
# CHECK5: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
# CHECK5-NEXT: NULL 0x000000 0x0000000000000000 0x0000000000000000 0x000078 0x001000 0x1
# CHECK5-EMPTY:
# CHECK5S: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
# CHECK5S-NEXT: NULL 0x000000 0x0000000000000000 0x0000000000000000 0x000078 0x001000 0x1
# CHECK5S-EMPTY:
--- !ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_DYN
Sections:
- Name: .foo
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC ]
Size: 0x01000
ProgramHeaders:
- Type: PT_NULL
Flags: []
FileSize: 0x01000
MemSize: 0x01000

21
llvm/tools/llvm-objcopy/ELF/Object.cpp
View File

@ -2315,18 +2315,19 @@ static uint64_t layoutSegmentsForOnlyKeepDebug(std::vector<Segment *> &Segments,
uint64_t HdrEnd) {
uint64_t MaxOffset = 0;
for (Segment *Seg : Segments) {
// An empty segment contains no section (see sectionWithinSegment). If it
// has a parent segment, copy the parent segment's offset field. This works
// for empty PT_TLS. We don't handle empty segments without a parent for
// now.
if (Seg->ParentSegment != nullptr && Seg->MemSize == 0)
Seg->Offset = Seg->ParentSegment->Offset;
const SectionBase *FirstSec = Seg->firstSection();
if (Seg->Type == PT_PHDR || !FirstSec)
if (Seg->Type == PT_PHDR)
continue;
uint64_t Offset = FirstSec->Offset;
// The segment offset is generally the offset of the first section.
//
// For a segment containing no section (see sectionWithinSegment), if it has
// a parent segment, copy the parent segment's offset field. This works for
// empty PT_TLS. If no parent segment, use 0: the segment is not useful for
// debugging anyway.
const SectionBase *FirstSec = Seg->firstSection();
uint64_t Offset =
FirstSec ? FirstSec->Offset
: (Seg->ParentSegment ? Seg->ParentSegment->Offset : 0);
uint64_t FileSize = 0;
for (const SectionBase *Sec : Seg->Sections) {
uint64_t Size = Sec->Type == SHT_NOBITS ? 0 : Sec->Size;