Check for a branded ELF note when OS/ABI is NONE

src/auditor/dynamic_linkage.jl

@@ -1,5 +1,30 @@
 using ObjectFile.ELF
 
+function os_from_elf_note(oh::ELFHandle)
+    for section in Sections(oh)
+        section_type(section) == ELF.SHT_NOTE || continue
+        seek(oh, section_offset(section))
+        name_length = read(oh, UInt32)
+        iszero(name_length) && continue
+        descriptor_length = read(oh, UInt32)
+        note_type = read(oh, UInt32)
+        name = String(read(oh, name_length - 1))  # skip trailing NUL
+        if note_type == 1
+            # Technically it's part of the Linux specification that any executable should
+            # have an ELF note with type 1, name GNU, and descriptor length ≥4, but in
+            # practice I haven't observed that consistently, especially on musl. So for
+            # now, only bother checking FreeBSD, which uses an ELF note rather than OS/ABI
+            # to identify itself on AArch64 and RISC-V.
+            if name == "FreeBSD" && descriptor_length == 4
+                return name
+            end
+        end
+    end
+    return nothing
+end
+
+os_from_elf_note(::ObjectHandle) = nothing
+
 """
     platform_for_object(oh::ObjectHandle)
 
@@ -39,7 +64,9 @@
             end
         end
 
-        if oh.ei.osabi == ELF.ELFOSABI_LINUX || oh.ei.osabi == ELF.ELFOSABI_NONE
+        if oh.ei.osabi == ELF.ELFOSABI_NONE
+            return Platform(arch, os_from_elf_note(oh) == "FreeBSD" ? "freebsd" : "linux")
+        elseif oh.ei.osabi == ELF.ELFOSABI_LINUX
             return Platform(arch, "linux")
         elseif oh.ei.osabi == ELF.ELFOSABI_FREEBSD
             return Platform(arch, "freebsd")
@@ -108,6 +135,13 @@
             else
                 error("Unknown OS ABI type $(typeof(platform))")
             end
+        else
+            # If no OSABI, check whether it has a matching ELF note
+            if Sys.isfreebsd(platform)
+                if os_from_elf_note(h) != "FreeBSD"
+                    return false
+                end
+            end
         end
         # Check that the ELF arch matches our own
         m = h.header.e_machine

src/auditor/extra_checks.jl

@@ -5,7 +5,19 @@ using Dates: DateTime, datetime2unix
 
 function check_os_abi(oh::ObjectHandle, p::AbstractPlatform, rest...; verbose::Bool = false, kwargs...)
     if Sys.isfreebsd(p)
-        if oh.ei.osabi != ELF.ELFOSABI_FREEBSD
+        # On AArch64 and RISC-V, FreeBSD uses an ELF note section to identify itself rather
+        # than OS/ABI in the ELF header. In that case, the OS/ABI will be generic Unix (NONE).
+        # See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=252490 and
+        # https://github.com/freebsd/freebsd-src/blob/main/lib/csu/common/crtbrand.S
+        if oh.ei.osabi == ELF.ELFOSABI_NONE
+            if os_from_elf_note(oh) != "FreeBSD"
+                if verbose
+                    @warn("$(basename(path(oh))) does not have a FreeBSD-branded ELF note " *
+                          "and may be unrecognized or unusable on $p")
+                end
+                return false
+            end
+        elseif oh.ei.osabi != ELF.ELFOSABI_FREEBSD
             # The dynamic loader should not have problems in this case, but the
             # linker may not appreciate.  Let the user know about this.
             if verbose
@@ -17,7 +29,8 @@ function check_os_abi(oh::ObjectHandle, p::AbstractPlatform, rest...; verbose::B
             end
             return false
         end
-    elseif call_abi(p) == "eabihf"
+    end
+    if call_abi(p) == "eabihf"
         # Make sure the object file has the hard-float ABI.  See Table 4-2 of
         # "ELF for the ARM Architecture" document
         # (https://developer.arm.com/documentation/ihi0044/e/).  Note: `0x000`

test/auditing.jl

@@ -1,5 +1,6 @@
 using BinaryBuilder.Auditor
-using BinaryBuilder.Auditor: compatible_marchs, valid_library_path
+using BinaryBuilder.Auditor: check_os_abi, compatible_marchs, is_for_platform, valid_library_path
+using ObjectFile
 
 # Tests for our auditing infrastructure
 
@@ -788,57 +789,134 @@ end
 end
 
 @testset "Auditor - other checks" begin
-    platform = Platform("armv7l", "linux"; call_abi = "eabihf", libc = "glibc")
-    mktempdir() do build_path
-        build_output_meta = @test_logs (:error, r"libsoft.so does not match the hard-float ABI") match_mode=:any begin
-            autobuild(
-                build_path,
-                "hard_float_ABI",
-                v"1.0.0",
-                # No sources
-                FileSource[],
-                # Build a library which doesn't link to the standard library and
-                # forces the soft-float ABI
-                raw"""
-                mkdir -p "${libdir}" "${bindir}"
-                # This library has hard-float ABI
-                echo 'int test() { return 0; }' | cc -shared -fPIC -o "${libdir}/libhard.${dlext}" -x c -
-                # This library has soft-float ABI
-                echo 'int _start() { return 0; }' | /opt/${target}/bin/${target}-gcc -nostdlib -shared -mfloat-abi=soft -o "${libdir}/libsoft.${dlext}" -x c -
-                # hello_world built by Go doesn't specify any float ABI
-                make -C /usr/share/testsuite/go/hello_world/
-                cp "/tmp/testsuite/${target}/go/hello_world/hello_world" "${bindir}/hello_world"
-                """,
-                # Build for Linux armv7l hard-float
-                [platform],
-                # Ensure our library product is built
-                [
-                    LibraryProduct("libhard", :libhard),
-                    LibraryProduct("libsoft", :libsoft),
-                    ExecutableProduct("hello_world", :hello_world),
-                ],
-                # No dependencies
-                Dependency[];
-                compilers = [:c, :go],
-                verbose = true,
-                require_license = false
-            )
+    @testset "hard-float ABI" begin
+        platform = Platform("armv7l", "linux"; call_abi = "eabihf", libc = "glibc")
+        mktempdir() do build_path
+            build_output_meta = @test_logs (:error, r"libsoft.so does not match the hard-float ABI") match_mode=:any begin
+                autobuild(
+                    build_path,
+                    "hard_float_ABI",
+                    v"1.0.0",
+                    # No sources
+                    FileSource[],
+                    # Build a library which doesn't link to the standard library and
+                    # forces the soft-float ABI
+                    raw"""
+                    mkdir -p "${libdir}" "${bindir}"
+                    # This library has hard-float ABI
+                    echo 'int test() { return 0; }' | cc -shared -fPIC -o "${libdir}/libhard.${dlext}" -x c -
+                    # This library has soft-float ABI
+                    echo 'int _start() { return 0; }' | /opt/${target}/bin/${target}-gcc -nostdlib -shared -mfloat-abi=soft -o "${libdir}/libsoft.${dlext}" -x c -
+                    # hello_world built by Go doesn't specify any float ABI
+                    make -C /usr/share/testsuite/go/hello_world/
+                    cp "/tmp/testsuite/${target}/go/hello_world/hello_world" "${bindir}/hello_world"
+                    """,
+                    # Build for Linux armv7l hard-float
+                    [platform],
+                    # Ensure our library product is built
+                    [
+                        LibraryProduct("libhard", :libhard),
+                        LibraryProduct("libsoft", :libsoft),
+                        ExecutableProduct("hello_world", :hello_world),
+                    ],
+                    # No dependencies
+                    Dependency[];
+                    compilers = [:c, :go],
+                    verbose = true,
+                    require_license = false
+                )
+            end
+
+            @test haskey(build_output_meta, platform)
+            tarball_path, tarball_hash = build_output_meta[platform][1:2]
+            @test isfile(tarball_path)
+
+            # Unpack it somewhere else
+            @test verify(tarball_path, tarball_hash)
+            testdir = joinpath(build_path, "testdir")
+            mkdir(testdir)
+            unpack(tarball_path, testdir)
+            # Remove libsoft.so, we want to run audit only on the other products
+            rm(joinpath(testdir, "lib", "libsoft.so"))
+            # Make sure `hello_world` passes the float ABI check even if it doesn't
+            # set `EF_ARM_ABI_FLOAT_HARD`.
+            @test Auditor.audit(Prefix(testdir); platform=platform, require_license=false)
         end
+    end
+    @testset "OS/ABI: $platform" for platform in [Platform("x86_64", "freebsd"),
+                                                  Platform("aarch64", "freebsd")]
+        mktempdir() do build_path
+            build_output_meta = @test_logs (:warn, r"Skipping binary analysis of lib/lib(nonote|badosabi)\.so \(incorrect platform\)") match_mode=:any begin
+                autobuild(
+                    build_path,
+                    "OSABI",
+                    v"4.2.0",
+                    # No sources
+                    FileSource[],
+                    # Build a library with a mismatched OS/ABI in the ELF header
+                    raw"""
+                    apk update
+                    apk add binutils
+                    mkdir -p "${libdir}"
+                    cd "${libdir}"
+                    echo 'int wrong() { return 0; }' | cc -shared -fPIC -o "libwrong.${dlext}" -x c -
+                    echo 'int right() { return 0; }' | cc -shared -fPIC -o "libright.${dlext}" -x c -
+                    cp "libwrong.${dlext}" "libnonote.${dlext}"
+                    # We only check for a branded ELF note when the OS/ABI is 0
+                    elfedit --output-osabi=none "libnonote.${dlext}"
+                    strip --remove-section=.note.tag "libnonote.${dlext}"
+                    mv "libwrong.${dlext}" "libbadosabi.${dlext}"
+                    # NetBSD runs anywhere, which implies that anything that runs is for NetBSD, right?
+                    elfedit --output-osabi=NetBSD "libbadosabi.${dlext}"
+                    """,
+                    [platform],
+                    # Ensure our library product is built
+                    [
+                        LibraryProduct("libbadosabi", :libbadosabi),
+                        LibraryProduct("libnonote", :libnonote),
+                        LibraryProduct("libright", :libright),
+                    ],
+                    # No dependencies
+                    Dependency[];
+                    verbose=true,
+                    require_license=false,
+                )
+            end
 
-        @test haskey(build_output_meta, platform)
-        tarball_path, tarball_hash = build_output_meta[platform][1:2]
-        @test isfile(tarball_path)
+            @test haskey(build_output_meta, platform)
+            tarball_path, tarball_hash = build_output_meta[platform][1:2]
+            @test isfile(tarball_path)
 
-        # Unpack it somewhere else
-        @test verify(tarball_path, tarball_hash)
-        testdir = joinpath(build_path, "testdir")
-        mkdir(testdir)
-        unpack(tarball_path, testdir)
-        # Remove libsoft.so, we want to run audit only on the other products
-        rm(joinpath(testdir, "lib", "libsoft.so"))
-        # Make sure `hello_world` passes the float ABI check even if it doesn't
-        # set `EF_ARM_ABI_FLOAT_HARD`.
-        @test Auditor.audit(Prefix(testdir); platform=platform, require_license=false)
+            # Unpack it somewhere else
+            @test verify(tarball_path, tarball_hash)
+            testdir = joinpath(build_path, "testdir")
+            mkdir(testdir)
+            unpack(tarball_path, testdir)
+            readmeta(joinpath(testdir, "lib", "libright.so")) do ohs
+                oh = only(ohs)
+                @test is_for_platform(oh, platform)
+                @test check_os_abi(oh, platform)
+            end
+            readmeta(joinpath(testdir, "lib", "libnonote.so")) do ohs
+                oh = only(ohs)
+                @test !is_for_platform(oh, platform)
+                @test !check_os_abi(oh, platform)
+                @test_logs((:warn, r"libnonote.so does not have a FreeBSD-branded ELF note"),
+                           match_mode=:any, check_os_abi(oh, platform; verbose=true))
+            end
+            readmeta(joinpath(testdir, "lib", "libbadosabi.so")) do ohs
+                oh = only(ohs)
+                @test !is_for_platform(oh, platform)
+                @test !check_os_abi(oh, platform)
+                @test_logs((:warn, r"libbadosabi.so has an ELF header OS/ABI value that is not set to FreeBSD"),
+                           match_mode=:any, check_os_abi(oh, platform; verbose=true))
+            end
+            # Only audit the library we didn't mess with in the recipe
+            for bad in ("nonote", "badosabi")
+                rm(joinpath(testdir, "lib", "lib$bad.so"))
+            end
+            @test Auditor.audit(Prefix(testdir); platform=platform, require_license=false)
+        end
     end
 end