elf: fix arithmetic overflow with invalid program headers (#320)

See m4b/goblin#306

src/elf.rs

@@ -639,6 +639,22 @@ impl<E: UserDefinedError, I: InstructionMeter> Executable<E, I> {
             config.static_syscalls = false;
         }
 
+        if config.enable_elf_vaddr {
+            // This is needed to avoid an overflow error in header.vm_range() as
+            // used by relocate(). See https://github.com/m4b/goblin/pull/306.
+            //
+            // Once we bump to a version of goblin that includes the fix, this
+            // check can be removed, and relocate() will still return
+            // ValueOutOfBounds on malformed program headers.
+            if elf
+                .program_headers
+                .iter()
+                .any(|header| header.p_vaddr.checked_add(header.p_memsz).is_none())
+            {
+                return Err(ElfError::ValueOutOfBounds);
+            }
+        }
+
         let num_text_sections =
             elf.section_headers
                 .iter()
@@ -2054,6 +2070,15 @@ mod test {
         .expect("validation failed");
     }
 
+    #[test]
+    #[should_panic(expected = "validation failed: ValueOutOfBounds")]
+    fn test_program_headers_overflow() {
+        let elf_bytes = std::fs::read("tests/elfs/program_headers_overflow.so")
+            .expect("failed to read elf file");
+        ElfExecutable::load(Config::default(), &elf_bytes, syscall_registry())
+            .expect("validation failed");
+    }
+
     #[cfg(all(not(windows), target_arch = "x86_64"))]
     #[test]
     fn test_size() {

tests/elfs/elfs.sh

@@ -90,3 +90,7 @@ rm syscall_static_unknown.o
 "$LLVM_DIR"clang -Werror -target sbf -mcpu=sbfv2 -O2 -fno-builtin -fPIC -o syscall_static.o -c syscall_static.c
 "$LLVM_DIR"ld.lld -z notext -shared --Bdynamic -entry entrypoint --script elf.ld -o syscall_static.so syscall_static.o
 rm syscall_static.o
+
+"$LLVM_DIR"clang -Werror -target sbf -mcpu=sbfv2 -O2 -fno-builtin -fPIC -o program_headers_overflow.o -c rodata.c
+"$LLVM_DIR"ld.lld -z notext -shared --Bdynamic -entry entrypoint --script program_headers_overflow.ld --noinhibit-exec -o program_headers_overflow.so program_headers_overflow.o
+rm program_headers_overflow.o

tests/elfs/program_headers_overflow.ld

@@ -0,0 +1,24 @@
+PHDRS
+{
+  text PT_LOAD ;
+  rodata PT_LOAD ;
+  data PT_LOAD ;
+  dynamic PT_DYNAMIC ;
+}
+
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+  .text 0xFFFFFFFFFFFFFFF0 : { *(.text*) } :text
+  .rodata : { *(.rodata*) } :rodata
+  .data.rel.ro : { *(.data.rel.ro*) } :rodata
+  .dynamic : { *(.dynamic) } :dynamic
+  .dynsym : { *(.dynsym) } :data
+  .dynstr : { *(.dynstr) } :data
+  .rel.dyn : { *(.rel.dyn) } :data
+  /DISCARD/ : {
+      *(.eh_frame*)
+      *(.gnu.hash*)
+      *(.hash*)
+    }
+}