[llvm] [llvm][MachO] Fix integer truncation in rebase/bind parsing (PR #89337)

[Zixu Wang via llvm-commits]

https://github.com/zixu-w created https://github.com/llvm/llvm-project/pull/89337

`Skip` could use up the full 64 bits decoded by `readULEB128` for some rebase/bind opcodes.
In `*_OPCODE_DO_*_ULEB_TIMES_SKIPPING_ULEB`, `Skip` could be encoded as a two's complement for moving `SegmentOffset` backwards. Having a 32-bit `Skip` truncates the encoded value and leads to a malformed `AdvanceAmount` and invalid `SegmentOffset` that extends past valid sections.

>From b43c97b292e192180408029f59b862f3502e5311 Mon Sep 17 00:00:00 2001
From: Zixu Wang <zixu_wang at apple.com>
Date: Thu, 18 Apr 2024 18:08:48 -0700
Subject: [PATCH] [llvm][MachO] Fix integer truncation in rebase/bind parsing

`Skip` could use up the full 64 bits decoded by `readULEB128` for some
rebase/bind opcodes.
In `*_OPCODE_DO_*_ULEB_TIMES_SKIPPING_ULEB`, `Skip` could be encoded as
a two's complement for moving `SegmentOffset` backwards. Having a 32-bit
`Skip` truncates the encoded value and leads to a malformed `AdvanceAmount`
and invalid `SegmentOffset` that extends past valid sections.
---
 llvm/include/llvm/Object/MachO.h    |  6 +++---
 llvm/lib/Object/MachOObjectFile.cpp | 20 +++++++++++++++-----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/llvm/include/llvm/Object/MachO.h b/llvm/include/llvm/Object/MachO.h
index 24f9954584ed5d..bf35d9c4e9905b 100644
--- a/llvm/include/llvm/Object/MachO.h
+++ b/llvm/include/llvm/Object/MachO.h
@@ -136,7 +136,7 @@ class BindRebaseSegInfo {
   // Used to check a Mach-O Bind or Rebase entry for errors when iterating.
   const char* checkSegAndOffsets(int32_t SegIndex, uint64_t SegOffset,
                                  uint8_t PointerSize, uint32_t Count=1,
-                                 uint32_t Skip=0);
+                                 uint64_t Skip=0);
   // Used with valid SegIndex/SegOffset values from checked entries.
   StringRef segmentName(int32_t SegIndex);
   StringRef sectionName(int32_t SegIndex, uint64_t SegOffset);
@@ -577,7 +577,7 @@ class MachOObjectFile : public ObjectFile {
   // This is used by MachOBindEntry::moveNext() to validate a MachOBindEntry.
   const char *BindEntryCheckSegAndOffsets(int32_t SegIndex, uint64_t SegOffset,
                                          uint8_t PointerSize, uint32_t Count=1,
-                                          uint32_t Skip=0) const {
+                                          uint64_t Skip=0) const {
     return BindRebaseSectionTable->checkSegAndOffsets(SegIndex, SegOffset,
                                                      PointerSize, Count, Skip);
   }
@@ -592,7 +592,7 @@ class MachOObjectFile : public ObjectFile {
                                             uint64_t SegOffset,
                                             uint8_t PointerSize,
                                             uint32_t Count=1,
-                                            uint32_t Skip=0) const {
+                                            uint64_t Skip=0) const {
     return BindRebaseSectionTable->checkSegAndOffsets(SegIndex, SegOffset,
                                                       PointerSize, Count, Skip);
   }
diff --git a/llvm/lib/Object/MachOObjectFile.cpp b/llvm/lib/Object/MachOObjectFile.cpp
index 1cfd0a069463e9..deeabef7e7501f 100644
--- a/llvm/lib/Object/MachOObjectFile.cpp
+++ b/llvm/lib/Object/MachOObjectFile.cpp
@@ -3515,7 +3515,12 @@ void MachORebaseEntry::moveNext() {
     uint8_t Byte = *Ptr++;
     uint8_t ImmValue = Byte & MachO::REBASE_IMMEDIATE_MASK;
     uint8_t Opcode = Byte & MachO::REBASE_OPCODE_MASK;
-    uint32_t Count, Skip;
+    uint32_t Count;
+    // For opcode REBASE_OPCODE_DO_REBASE_ULEB_TIMES_SKIPPING_ULEB, the ULEB128
+    // encoded Skip amount could be two's complements for moving SegmentOffset
+    // to a lower address. Skip should be the same integer width as
+    // SegmentOffset and AdvanceAmount to prevent truncating.
+    uint64_t Skip;
     const char *error = nullptr;
     switch (Opcode) {
     case MachO::REBASE_OPCODE_DONE:
@@ -3854,7 +3859,12 @@ void MachOBindEntry::moveNext() {
     uint8_t Opcode = Byte & MachO::BIND_OPCODE_MASK;
     int8_t SignExtended;
     const uint8_t *SymStart;
-    uint32_t Count, Skip;
+    uint32_t Count;
+    // For opcode BIND_OPCODE_DO_BIND_ULEB_TIMES_SKIPPING_ULEB, the ULEB128
+    // encoded Skip amount could be two's complements for moving SegmentOffset
+    // to a lower address. Skip should be the same integer width as
+    // SegmentOffset and AdvanceAmount to prevent truncating.
+    uint64_t Skip;
     const char *error = nullptr;
     switch (Opcode) {
     case MachO::BIND_OPCODE_DONE:
@@ -4388,14 +4398,14 @@ const char * BindRebaseSegInfo::checkSegAndOffsets(int32_t SegIndex,
                                                    uint64_t SegOffset,
                                                    uint8_t PointerSize,
                                                    uint32_t Count,
-                                                   uint32_t Skip) {
+                                                   uint64_t Skip) {
   if (SegIndex == -1)
     return "missing preceding *_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB";
   if (SegIndex >= MaxSegIndex)
     return "bad segIndex (too large)";
   for (uint32_t i = 0; i < Count; ++i) {
-    uint32_t Start = SegOffset + i * (PointerSize + Skip);
-    uint32_t End = Start + PointerSize;
+    uint64_t Start = SegOffset + i * (PointerSize + Skip);
+    uint64_t End = Start + PointerSize;
     bool Found = false;
     for (const SectionInfo &SI : Sections) {
       if (SI.SegmentIndex != SegIndex)