elf: error out if sbpf_version.enable_elf_vaddr() and config.optimize…

…_rodata=false (#478)

Enabling virtual addresses requires optimize_rodata=true. Otherwise with
optimize_rodata=false we allocate a vec where we join all the readonly
sections, and if we allowed virtual addresses then we'd potentially have
to allocate huge amounts of memory.

src/elf.rs

@@ -718,6 +718,13 @@ impl<V: Verifier, C: ContextObject> Executable<V, C> {
         };
 
         if sbpf_version.enable_elf_vaddr() {
+            if !config.optimize_rodata {
+                // When optimize_rodata=false, we allocate a vector and copy all
+                // rodata sections into it. In that case we can't allow virtual
+                // addresses or we'd potentially have to do huge allocations.
+                return Err(ElfError::UnsupportedSBPFVersion);
+            }
+
             // This is needed to avoid an overflow error in header.vm_range() as
             // used by relocate(). See https://github.com/m4b/goblin/pull/306.
             //
@@ -845,6 +852,8 @@ impl<V: Verifier, C: ContextObject> Executable<V, C> {
             // sh_offset for backwards compatibility
             if !invalid_offsets {
                 if sbpf_version.enable_elf_vaddr() {
+                    // This is enforced in validate()
+                    debug_assert!(config.optimize_rodata);
                     if section_addr < section_header.sh_offset() {
                         invalid_offsets = true;
                     } else {
@@ -1969,8 +1978,9 @@ mod test {
             (Some(b".dynamic"), &s2),
             (Some(b".rodata"), &s3),
         ];
+        // V2 requires optimize_rodata=true
         let ro_section =
-            ElfExecutable::parse_ro_sections(&config, &SBPFVersion::V2, sections, &elf_bytes)
+            ElfExecutable::parse_ro_sections(&config, &SBPFVersion::V1, sections, &elf_bytes)
                 .unwrap();
         let ro_region = get_ro_region(&ro_section, &elf_bytes);
         let owned_section = match &ro_section {
@@ -2069,7 +2079,7 @@ mod test {
         assert!(matches!(
             ElfExecutable::parse_ro_sections(
                 &config,
-                &SBPFVersion::V2,
+                &SBPFVersion::V1, // v2 requires optimize_rodata=true
                 sections,
                 &elf_bytes,
             ),

tests/elfs/elfs.sh

@@ -81,6 +81,10 @@ rm bss_section.o
 "$LLVM_DIR"ld.lld $LD_FLAGS -o rodata.so rodata.o
 rm rodata.o
 
+"$LLVM_DIR"clang $CC_FLAGS -mcpu=generic -o rodata.o -c rodata.c
+"$LLVM_DIR"ld.lld $LD_FLAGS -o rodata_sbpfv1.so rodata.o
+rm rodata.o
+
 "$LLVM_DIR"clang $CC_FLAGS -o rodata_high_vaddr.o -c rodata.c
 "$LLVM_DIR"ld.lld -z notext -shared --Bdynamic -entry entrypoint --nmagic --section-start=.text=0x100000000 --section-start=.rodata=0x100000020 -o rodata_high_vaddr.so rodata_high_vaddr.o
 rm rodata_high_vaddr.o

tests/execution.rs

@@ -3097,23 +3097,35 @@ fn test_load_elf_empty_rodata() {
 }
 
 #[test]
-fn test_load_elf_rodata() {
-    // checks that the program loads the correct rodata offset with both
-    // borrowed and owned rodata
-    for optimize_rodata in [false, true] {
-        let config = Config {
-            optimize_rodata,
-            ..Config::default()
-        };
-        test_interpreter_and_jit_elf!(
-            "tests/elfs/rodata.so",
-            config,
-            [],
-            (),
-            TestContextObject::new(3),
-            ProgramResult::Ok(42),
-        );
-    }
+fn test_load_elf_rodata_sbpfv2() {
+    let config = Config {
+        optimize_rodata: true,
+        ..Config::default()
+    };
+    test_interpreter_and_jit_elf!(
+        "tests/elfs/rodata.so",
+        config,
+        [],
+        (),
+        TestContextObject::new(3),
+        ProgramResult::Ok(42),
+    );
+}
+
+#[test]
+fn test_load_elf_rodata_sbpfv1() {
+    let config = Config {
+        optimize_rodata: false,
+        ..Config::default()
+    };
+    test_interpreter_and_jit_elf!(
+        "tests/elfs/rodata_sbpfv1.so",
+        config,
+        [],
+        (),
+        TestContextObject::new(3),
+        ProgramResult::Ok(42),
+    );
 }
 
 #[test]