[msan] Add 'MappingDesc::ALLOCATOR' type and check it is available

[thurstond]

MSan divides the virtual address space into APP, INVALID, SHADOW and ORIGIN memory. The allocator usually just steals a bit of the APP address space: typically the bottom portion of the PIE binaries section, which works because the Linux kernel maps from the top of the PIE binaries section. However, if ASLR is very aggressive, the binary may end up mapped in the same location where the allocator wants to live; this results in a segfault.

This patch adds in a MappingDesc::ALLOCATOR type and enforces that the memory range for the allocator is not occupied by anything else.

Since the allocator range information is not readily available in msan.h, we duplicate the information from msan_allocator.cpp.

Note: aggressive ASLR can also lead to a different type of failure, where the PIE binaries/libraries are mapped entirely outside of the APP/ALLOCATOR sections; that will be addressed in a separate patch (#85142).

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Thurston Dang (thurstond)

Changes

MSan divides the virtual address space into APP, INVALID, SHADOW and ORIGIN memory. The allocator usually just steals a bit of the APP address space: typically the bottom portion of the PIE binaries section, which works because the Linux kernel maps from the top of the PIE binaries section. However, if ASLR is very aggressive, the binary may end up mapped in the same location where the allocator wants to live; this results in a segfault.

This patch adds in a MappingDesc::ALLOCATOR type and enforces that the memory range for the allocator is not occupied by anything else.

Since the allocator range information is not readily available in msan.h, we duplicate the information from msan_allocator.cpp.

Note: aggressive ASLR can also lead to a different type of failure, where the PIE binaries/libaries are mapped entirely outside of the APP/ALLOCATOR sections; that will be addressed in a separate patch (#85142).

---

Full diff: https://github.com/llvm/llvm-project/pull/85153.diff

3 Files Affected:

• (modified) compiler-rt/lib/msan/msan.h (+17-10)
• (modified) compiler-rt/lib/msan/msan_allocator.cpp (+3)
• (modified) compiler-rt/lib/msan/msan_linux.cpp (+8-3)

diff --git a/compiler-rt/lib/msan/msan.h b/compiler-rt/lib/msan/msan.h
index 710447a3e1a357..d9bed5acb1f0d8 100644
--- a/compiler-rt/lib/msan/msan.h
+++ b/compiler-rt/lib/msan/msan.h
@@ -32,13 +32,13 @@
 struct MappingDesc {
   uptr start;
   uptr end;
-  enum Type {
-    INVALID, APP, SHADOW, ORIGIN
-  } type;
+  enum Type { INVALID, ALLOCATOR, APP, SHADOW, ORIGIN } type;
   const char *name;
 };
 
-
+// Note: MappingDesc::ALLOCATOR entries are only used to check for memory
+// layout compatibility. The actual allocation settings are in
+// msan_allocator.cpp, which need to be kept in sync.
 #if SANITIZER_LINUX && defined(__mips64)
 
 // MIPS64 maps:
@@ -84,7 +84,8 @@ const MappingDesc kMemoryLayout[] = {
     {0X0B00000000000, 0X0C00000000000, MappingDesc::SHADOW, "shadow-10-13"},
     {0X0C00000000000, 0X0D00000000000, MappingDesc::INVALID, "invalid"},
     {0X0D00000000000, 0X0E00000000000, MappingDesc::ORIGIN, "origin-10-13"},
-    {0X0E00000000000, 0X1000000000000, MappingDesc::APP, "app-15"},
+    {0x0E00000000000, 0x0E40000000000, MappingDesc::ALLOCATOR, "allocator"},
+    {0X0E40000000000, 0X1000000000000, MappingDesc::APP, "app-15"},
 };
 # define MEM_TO_SHADOW(mem) ((uptr)mem ^ 0xB00000000000ULL)
 # define SHADOW_TO_ORIGIN(shadow) (((uptr)(shadow)) + 0x200000000000ULL)
@@ -106,7 +107,8 @@ const MappingDesc kMemoryLayout[] = {
     {0x510000000000ULL, 0x600000000000ULL, MappingDesc::APP, "app-2"},
     {0x600000000000ULL, 0x610000000000ULL, MappingDesc::ORIGIN, "origin-1"},
     {0x610000000000ULL, 0x700000000000ULL, MappingDesc::INVALID, "invalid"},
-    {0x700000000000ULL, 0x800000000000ULL, MappingDesc::APP, "app-3"}};
+    {0x700000000000ULL, 0x740000000000ULL, MappingDesc::ALLOCATOR, "allocator"},
+    {0x740000000000ULL, 0x800000000000ULL, MappingDesc::APP, "app-3"}};
 #  define MEM_TO_SHADOW(mem) (((uptr)(mem)) ^ 0x500000000000ULL)
 #  define SHADOW_TO_ORIGIN(shadow) (((uptr)(shadow)) + 0x100000000000ULL)
 
@@ -118,7 +120,8 @@ const MappingDesc kMemoryLayout[] = {
     {0x180200000000ULL, 0x1C0000000000ULL, MappingDesc::INVALID, "invalid"},
     {0x1C0000000000ULL, 0x2C0200000000ULL, MappingDesc::ORIGIN, "origin"},
     {0x2C0200000000ULL, 0x300000000000ULL, MappingDesc::INVALID, "invalid"},
-    {0x300000000000ULL, 0x800000000000ULL, MappingDesc::APP, "high memory"}};
+    {0x300000000000ULL, 0x320000000000ULL, MappingDesc::ALLOCATOR, "allocator"},
+    {0x320000000000ULL, 0x800000000000ULL, MappingDesc::APP, "high memory"}};
 
 // Various kernels use different low end ranges but we can combine them into one
 // big range. They also use different high end ranges but we can map them all to
@@ -141,7 +144,8 @@ const MappingDesc kMemoryLayout[] = {
     {0x180000000000ULL, 0x1C0000000000ULL, MappingDesc::INVALID, "invalid"},
     {0x1C0000000000ULL, 0x2C0000000000ULL, MappingDesc::ORIGIN, "origin"},
     {0x2C0000000000ULL, 0x440000000000ULL, MappingDesc::INVALID, "invalid"},
-    {0x440000000000ULL, 0x500000000000ULL, MappingDesc::APP, "high memory"}};
+    {0x440000000000ULL, 0x460000000000ULL, MappingDesc::ALLOCATOR, "allocator"},
+    {0x460000000000ULL, 0x500000000000ULL, MappingDesc::APP, "high memory"}};
 
 #define MEM_TO_SHADOW(mem) \
   ((((uptr)(mem)) & ~0xC00000000000ULL) + 0x080000000000ULL)
@@ -208,7 +212,8 @@ const MappingDesc kMemoryLayout[] = {
     {0x510000000000ULL, 0x600000000000ULL, MappingDesc::APP, "app-2"},
     {0x600000000000ULL, 0x610000000000ULL, MappingDesc::ORIGIN, "origin-1"},
     {0x610000000000ULL, 0x700000000000ULL, MappingDesc::INVALID, "invalid"},
-    {0x700000000000ULL, 0x800000000000ULL, MappingDesc::APP, "app-3"}};
+    {0x700000000000ULL, 0x740000000000ULL, MappingDesc::ALLOCATOR, "allocator"},
+    {0x740000000000ULL, 0x800000000000ULL, MappingDesc::APP, "app-3"}};
 #define MEM_TO_SHADOW(mem) (((uptr)(mem)) ^ 0x500000000000ULL)
 #define SHADOW_TO_ORIGIN(mem) (((uptr)(mem)) + 0x100000000000ULL)
 
@@ -236,7 +241,9 @@ inline bool addr_is_type(uptr addr, MappingDesc::Type mapping_type) {
   return false;
 }
 
-#define MEM_IS_APP(mem) addr_is_type((uptr)(mem), MappingDesc::APP)
+#define MEM_IS_APP(mem)                           \
+  (addr_is_type((uptr)(mem), MappingDesc::APP) || \
+   addr_is_type((uptr)(mem), MappingDesc::ALLOCATOR))
 #define MEM_IS_SHADOW(mem) addr_is_type((uptr)(mem), MappingDesc::SHADOW)
 #define MEM_IS_ORIGIN(mem) addr_is_type((uptr)(mem), MappingDesc::ORIGIN)
 
diff --git a/compiler-rt/lib/msan/msan_allocator.cpp b/compiler-rt/lib/msan/msan_allocator.cpp
index 0b2dd2b2f1883d..b1bc5b9390f75b 100644
--- a/compiler-rt/lib/msan/msan_allocator.cpp
+++ b/compiler-rt/lib/msan/msan_allocator.cpp
@@ -48,6 +48,9 @@ struct MsanMapUnmapCallback {
   }
 };
 
+// Note: to ensure that the allocator is compatible with the application memory
+// layout (especially with high-entropy ASLR), kSpaceBeg and kSpaceSize must be
+// duplicated as MappingDesc::ALLOCATOR in msan.h.
 #if defined(__mips64)
 static const uptr kMaxAllowedMallocSize = 2UL << 30;
 
diff --git a/compiler-rt/lib/msan/msan_linux.cpp b/compiler-rt/lib/msan/msan_linux.cpp
index c7ecb7cad56661..b02994c4c13353 100644
--- a/compiler-rt/lib/msan/msan_linux.cpp
+++ b/compiler-rt/lib/msan/msan_linux.cpp
@@ -86,7 +86,7 @@ static void CheckMemoryLayoutSanity() {
     CHECK(addr_is_type(start, type));
     CHECK(addr_is_type((start + end) / 2, type));
     CHECK(addr_is_type(end - 1, type));
-    if (type == MappingDesc::APP) {
+    if (type == MappingDesc::APP || type == MappingDesc::ALLOCATOR) {
       uptr addr = start;
       CHECK(MEM_IS_SHADOW(MEM_TO_SHADOW(addr)));
       CHECK(MEM_IS_ORIGIN(MEM_TO_ORIGIN(addr)));
@@ -138,8 +138,13 @@ bool InitShadow(bool init_origins) {
     bool protect = type == MappingDesc::INVALID ||
                    (!init_origins && type == MappingDesc::ORIGIN);
     CHECK(!(map && protect));
-    if (!map && !protect)
-      CHECK(type == MappingDesc::APP);
+    if (!map && !protect) {
+      CHECK(type == MappingDesc::APP || type == MappingDesc::ALLOCATOR);
+
+      if (type == MappingDesc::ALLOCATOR &&
+          !CheckMemoryRangeAvailability(start, size))
+        return false;
+    }
     if (map) {
       if (!CheckMemoryRangeAvailability(start, size))
         return false;