Joseph Ferano
92fae67fb3
The sweep's note said there was no Flan program that reached flan_dyn.c, so the only sanitized run over the collector was dyn_ops.c's -- which pushes its roots by hand. That note stopped being true when the dyn programs landed, and it stayed in the file. The gap it left is the one that matters for the backend lane just committed: a root the *emitter* forgot is a live object swept, and no amount of C testing can see a mistake the compiler made. dyn-vec and dyn-defer are in the corpus now -- the second for the roots that come off on a transfer's path out rather than a return's -- and so is p13-dyn-collect, which is the only program anywhere that allocates past flan_dyn.c's one-megabyte floor and therefore the only one under which a mark and a sweep actually run. Everything else in that list agrees with ASan by never collecting at all. p13 lives in spike/x86 because that is the lane that wrote it, so the alias's deps grew a glob for that directory; it is in this sweep for what it does and not for where it sits. What this cannot cover, and the compiler says so itself when asked: there is no sanitizer pass over hand-written assembly, so --x86 --sanitize is refused by name. ASan sees the x86 lane's roots only from the collector's side of the call, never as frame slots. p13 through --x86 under the @x86 sweep is what stands in for it, and it is a weaker check honestly labelled rather than a stronger one assumed. --force @sanitize: clean, and non-empty, which the previous run was not -- an alias satisfied from cache prints nothing and reads exactly like a pass. dune test --force still green.
393 lines
19 KiB
OCaml
393 lines
19 KiB
OCaml
(* The corpus a second time, under AddressSanitizer and
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UndefinedBehaviorSanitizer.
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Not part of [dune test] and deliberately so: a sanitized build of one
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program is a 1.8MB statically linked binary and takes ten to twenty seconds
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to produce, so the sweep is minutes where the whole existing suite is
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seconds. It has its own alias.
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dune build --root . @sanitize
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What this can and cannot see is written down in [Build.opts] and in
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[Emit]'s [sanitize] comment, and it is not symmetric:
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- ASan reaches Flan code, but only because [Emit] puts [sanitize_address]
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on every function it defines; the attribute is what the pass selects on
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and hand-written IR has none by default. The positive control for that is
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[oob], below, which must report.
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- UBSan reaches the runtime's C and nothing else. Its checks are branches
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clang's *frontend* emits, and no attribute asks an LLVM pass to produce
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them, so the shift-past-the-width and float-cast questions this sweep was
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partly meant to answer are not answerable this way. [shift] records that
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as a test rather than as a paragraph: it is a program with unambiguous
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shift UB in it, and it is expected *not* to be caught.
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The check is two-sided. A marker in the sanitized run's output is a
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failure, and so is any divergence from the unsanitized run — same output,
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same exit status. The second half is not redundant: UBSan recovers by
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default, so a program can trip a check, carry on with a different value and
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still exit 0, and several of these programs exit nonzero by design, so
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"exit status 0" is not available as a pass condition. *)
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open Flan
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(* The watchdog first: a hang is the one failure mode that reports
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nothing at all. See watchdog.ml. *)
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let () = Watchdog.arm ~seconds:3600 "test_sanitize"
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let failures = ref 0
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let fail fmt =
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Printf.ksprintf (fun s -> incr failures; print_endline ("FAIL " ^ s)) fmt
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let scratch = Filename.get_temp_dir_name ()
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(* Leaks are off. Every allocation in the runtime is allocate-once-never-free
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by design — [rt_args] says so in its own comment — so LeakSanitizer here
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produces a suppression list and no information. Set in the environment
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rather than baked in, so a session asking the leak question can ask it.
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[print_stacktrace] is what turns a UBSan report from a source line into
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something with a caller in it, and it is off by default. *)
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let env =
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"ASAN_OPTIONS=${ASAN_OPTIONS:-detect_leaks=0} \
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UBSAN_OPTIONS=${UBSAN_OPTIONS:-print_stacktrace=1} "
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let run exe args =
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let out = Filename.concat scratch "flan-sanitize.out" in
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let cmd =
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Printf.sprintf "%s%s %s > %s 2>&1" env (Filename.quote exe)
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(String.concat " " (List.map Filename.quote args))
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(Filename.quote out)
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in
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let code = Sys.command cmd in
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let text = In_channel.with_open_bin out In_channel.input_all in
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(try Sys.remove out with Sys_error _ -> ());
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(code, text)
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let compile ~sanitize ~checks path =
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let exe =
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Filename.concat scratch
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(Printf.sprintf "flan-san-%s-%s"
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(if sanitize then "s" else "p")
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(Filename.remove_extension (Filename.basename path)))
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in
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let l = Load.program ~file:path (Reader.read_file path) in
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let p = Check.program l.Load.decls in
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let p, csrcs, lflags = Reach.link ~dev:false l p in
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ignore
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(Build.executable
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~opts:{ Build.default with checks; sanitize } ~csrcs ~lflags p ~out:exe);
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exe
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let contains hay needle =
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let n = String.length needle and h = String.length hay in
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let rec go i = i + n <= h && (String.sub hay i n = needle || go (i + 1)) in
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go 0
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(* What a report looks like, whichever sanitizer wrote it. *)
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let markers =
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[ "ERROR: AddressSanitizer"; "runtime error:"; "ERROR: LeakSanitizer";
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"SUMMARY: UndefinedBehaviorSanitizer" ]
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let reported text = List.exists (contains text) markers
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(* The corpus. Excluded, with the reason, rather than quietly absent:
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- raylib-*, and the windowed examples, because raylib and libm are not
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instrumented and every report through them would be about somebody
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else's code.
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- break.flan and agent.flan, which stop in the break loop and wait for an
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editor to connect. They are covered by test_agent against a real daemon.
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- the dev-* and reload-* programs, which need a host process or a dlopen
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harness. The reload path is half-covered at best in any case: a
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redefinition module is built by llc and ld, not by clang, so nothing
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instruments it — one more thing this sweep does not prove.
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- nth-gone, pkg-hidden-main, pkg-two-aliases, pkg-two-mains, pkg-cycle,
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which are negative cases and are expected not to compile.
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calc-me is here and is not in test/programs: it is the one string parser in
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the corpus, which makes it the likeliest to push [scratch] or [escaped]
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anywhere near their bounds. *)
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let corpus =
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[ (* bounds.flan selects its case from argv, and every case but 0 is one
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that traps. Argument 0 is the in-bounds path — the last index of a
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fixed array, a slice ending exactly at len, an empty slice at len —
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which is the one the sweep has something to say about. The trapping
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cases are where the ASan-without-bounds-checks question lives and they
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are run separately; see [unchecked_controls]. Running this program with
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*no* argument reads args[1] of a one-element argv, which is a bug in
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the harness rather than in anything under test. *)
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"programs/bounds.flan", [ "0" ];
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"programs/arena-value.flan", [];
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(* Here for what it would catch rather than for what it prints: the three
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number conversions render into a frame slot the checker allocates per
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call site, and a slot that ended up as a reclaimed temporary instead
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would be a stack-use-after-scope — which is exactly what ASan sees and
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an output comparison does not. *)
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"programs/two-numbers.flan", [];
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"programs/arena-edn.flan", [];
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"programs/bytes2.flan", [];
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"programs/cleanup.flan", [];
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"programs/conditions.flan", [];
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"programs/debug.flan", [];
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"programs/debug-permuted.flan", [];
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"programs/destructure.flan", [];
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"programs/edn.flan", [];
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(* The copy edn/read makes of every string: the document is read out of a
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(Vec u8) that is then overwritten in place, so a reader still holding
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views is reading a buffer it does not own and ASan is what says so. *)
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"programs/edn-read.flan", [];
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"programs/enum-compare.flan", [];
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"programs/error.flan", [];
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(* Makes and removes its own tree, so the two runs of the sweep see the
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same directory; the new C here is three more path buffers, which is
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exactly what this tool is for. *)
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"programs/files.flan", [];
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(* The JSON reader, which is the corpus's densest allocator: every string
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in the document is a (Vec u8) grown a byte at a time and then handed
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out as a view of its own block, and the block is never freed because
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the view IS the answer. ASan is what says the view still points at the
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block after the growth that moved it. *)
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"programs/json.flan", [];
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"programs/machine.flan", [];
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"programs/math.flan", [];
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"programs/math3.flan", [];
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"programs/pkg-diamond.flan", [];
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"programs/pkg-return.flan", [];
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"programs/pkg-shared.flan", [];
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"programs/pkg-unused.flan", [];
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"programs/printers.flan", [];
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"programs/println.flan", [];
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"programs/restarts.flan", [];
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(* The dyn programs, which reach flan_dyn.c from Flan rather than from the
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hand-written C below — and the difference is the whole reason they are
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here. [dyn_sweep] checks the collector against roots dyn_ops.c pushes
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by hand; these check it against the roots the *compiler* emits, which
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is the half no C test can reach. A root the emitter forgot is a live
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object swept, and that is a use-after-free with the collector's own
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hands on it.
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[dyn-vec] is the one that builds objects of three kinds; [dyn-defer]
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is the one whose roots come off on a transfer's path out rather than a
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return's, which is where a pop written on one path only would show.
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[p13] is the only program anywhere that allocates past flan_dyn.c's
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one-megabyte floor, so it is the only one where a mark and a sweep
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actually run — everything else in this list agrees with ASan by never
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collecting at all. *)
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"programs/dyn-vec.flan", [];
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"programs/dyn-defer.flan", [];
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"../spike/x86/p13-dyn-collect.flan", [];
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"programs/sand-headless.flan", [];
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"programs/signedness.flan", [];
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"programs/slices.flan", [];
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"programs/string-of-bytes.flan", [];
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"programs/text.flan", [];
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(* The clock and getenv. getenv hands back a slice viewing the process
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environment and never a copy, so a report here would be the one that
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matters. *)
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"programs/time.flan", [];
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"programs/unit-main.flan", [];
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"programs/utf8.flan", [];
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"programs/values.flan", [];
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"programs/virtual-controls-headless.flan", [];
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"../calc-me.flan", [ "1 + 2 * (3 - 0.5) / 2" ] ]
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let sweep ~checks label =
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List.iter
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(fun (path, args) ->
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match compile ~sanitize:false ~checks path with
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| exception Failure m -> fail "%s %s: unsanitized build: %s" label path m
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| plain ->
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(match compile ~sanitize:true ~checks path with
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| exception Failure m -> fail "%s %s: sanitized build: %s" label path m
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| san ->
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let c1, t1 = run plain args in
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let c2, t2 = run san args in
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if reported t2 then
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fail "%s %s: sanitizer report\n%s" label path t2
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else if c1 <> c2 || t1 <> t2 then
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fail "%s %s: diverged from the unsanitized run\n \
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plain (exit %d): %S\n sanitized (exit %d): %S"
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label path c1 t1 c2 t2;
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(try Sys.remove plain with Sys_error _ -> ());
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(try Sys.remove san with Sys_error _ -> ())))
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corpus
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(* The dyn runtime, under the same two sanitizers, driven from C. There are
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Flan programs that reach flan_dyn.c now and three of them are in [corpus]
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above — this used to say there were none — but they are a different
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question and not a replacement for this one. They exercise the roots the
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*compiler* emits, over the handful of operations a program happens to
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write; this exercises every entry point in the header, with the roots
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pushed by hand so that the runtime can be wrong on its own. The thing to
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build is test/dyn_ops.c against programs/dyn-host.flan — the same pair
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test_dyn.ml builds, with [sanitize] on.
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This is the case the sweep is most likely to have something to say about.
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Every other program in the corpus allocates and never frees, which is a
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policy ASan can only agree with; this one frees, and a mark-sweep collector
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is precisely a machine for freeing something that is still reachable. A
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use-after-free here is what a wrong marker looks like from the outside, and
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it is invisible to the assertions in test_dyn.ml — the freed bytes are
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usually still the bytes that were there.
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The leak question is not asked, for the reason [env] gives: leaks are off
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across this file because the runtime's allocations are allocate-once by
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design. It would be the wrong question here anyway — the temporaries ring
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holds the last sixty-four objects alive on purpose and at exit, and every
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one of them would be reported.
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Only the modes that return are run. The refusals end in [_exit(134)], which
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skips ASan's exit-time checks entirely, so running them would prove nothing
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the checked build has not already proved. *)
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let dyn_sweep () =
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let exe = Filename.concat scratch "flan-san-dyn" in
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let path = "programs/dyn-host.flan" in
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let l = Load.program ~file:path (Reader.read_file path) in
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let p = Check.program l.Load.decls in
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let p, csrcs, lflags = Reach.link ~dev:false l p in
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match
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Build.executable
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~opts:{ Build.default with Build.sanitize = true }
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~csrcs:(csrcs @ [ "dyn_ops.c" ]) ~lflags p ~out:exe
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with
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| exception Failure m -> fail "dyn: sanitized build: %s" m
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| _ ->
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List.iter
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(fun mode ->
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let code, text = run exe [ mode ] in
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if reported text then fail "dyn %s: sanitizer report\n%s" mode text
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else if code <> 0 then
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fail "dyn %s: exit %d under the sanitizers\n%s" mode code text)
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[ "ops"; "gc"; "unrooted"; "nested"; "sharing" ];
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(try Sys.remove exe with Sys_error _ -> ())
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(* The positive controls, which are the only evidence that a clean sweep means
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anything. Both are written here rather than kept in test/programs because
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neither is a program anybody should build: one reads off the end of an
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array and the other shifts an i32 by 32. *)
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let control ~expect_report ?(args = []) ~why name src =
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let path = Filename.concat scratch (name ^ ".flan") in
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Out_channel.with_open_bin path (fun ch -> Out_channel.output_string ch src);
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let exe = compile ~sanitize:true ~checks:false path in
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let _, text = run exe args in
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(match expect_report, reported text with
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| true, false -> fail "control %s: nothing reported. %s\n%s" name why text
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| false, true -> fail "control %s: reported. %s\n%s" name why text
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| _ -> ());
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(try Sys.remove exe with Sys_error _ -> ());
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(try Sys.remove path with Sys_error _ -> ())
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(* The variant the checked build cannot ask for: with Flan's own bounds checks
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off, is ASan enough on its own? bounds.flan is the program to ask it with —
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every one of its selectors is a deliberate out-of-bounds access, and in a
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checked build every one of them traps.
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The answer is no, and it is worth having the shape of the no. [reports]
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holds the cases ASan catches; the rest are listed with why it does not, and
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they are printed rather than asserted, because a future LLVM that folds
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differently would change them and that is information, not a regression.
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[9] is the one that is not about ASan at all: at -O2 the access never
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happens. The index is out of bounds on an [inbounds] getelementptr into a
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string constant, so the whole load folds to zero and the program prints a
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wrong answer instead of touching a redzone. At -O0, with the load still in
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the program, ASan reports it. That divergence is why [--sanitize] does not
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force -O0 the way [--debug] does — the optimiser is half of what is being
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measured. *)
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let unchecked_controls () =
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let reports = [ "3"; "7"; "4" ] in
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let silent =
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[ "-1", "a negative index into a global. Not a property of the access: \
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ASan lays a global out as {data, redzone}, so an underflow is \
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caught when something redzoned precedes it and not when nothing \
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does — measured both ways, and here nothing does. Whether \
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reading before an array is seen at all is therefore up to what \
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the linker put in front of it";
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"9", "at -O2 the load is folded away — an out-of-bounds inbounds GEP \
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into a string constant is poison, so nothing is read and a wrong \
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value is printed. Reported at -O0.";
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"2", "a reversed slice (lo 2, hi 1), which this build traps on before \
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anything is read. It is in this list rather than out of it \
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because it used to be here for the opposite reason: the length \
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came out negative, nothing was read, and ASan had nothing to \
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see, which made a slice with a negative length reaching user \
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code a checker question and not a sanitizer one. The checker \
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answered it — lo <= hi is a representation invariant and no \
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longer sits behind --no-bounds-checks — so ASan is still silent \
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here and now for a better reason. The trap itself is asserted in \
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test_acceptance.ml" ]
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in
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match compile ~sanitize:true ~checks:false "programs/bounds.flan" with
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| exception Failure m -> fail "unchecked bounds.flan: build: %s" m
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| exe ->
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List.iter
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(fun a ->
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let _, t = run exe [ a ] in
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if not (reported t) then
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fail "unchecked bounds.flan %s: nothing reported, and this is the \
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case that says ASan sees an unchecked build at all\n%s" a t)
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reports;
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List.iter
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(fun (a, why) ->
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let _, t = run exe [ a ] in
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if reported t then
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Printf.printf
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"note unchecked bounds.flan %s now reports; it did not, on the \
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grounds that %s\n" a why
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else
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Printf.printf "note unchecked bounds.flan %s: silent — %s\n" a why)
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silent;
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(try Sys.remove exe with Sys_error _ -> ())
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let () =
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match Sys.command "command -v clang > /dev/null 2>&1" with
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| 0 ->
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(* A read one past the end of a four-element global. Index 5 and not 9,
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and the difference is worth knowing: ASan registers this array as
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"16 bytes in a 32-byte slot", so the poisoned redzone is bytes 16..31.
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Index 5 is byte 20 and is caught; index 9 is byte 36, past the
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registration entirely, and is silent. Overrunning a small object by
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enough lands back in ordinary memory. *)
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control ~expect_report:true "flan-san-ctl-oob"
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~why:"This sweep is not instrumenting Flan code at all — check that \
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Emit still puts every define in the sanitize_address attribute \
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group, without which -fsanitize=address covers the runtime's C \
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and nothing else."
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"(defvar arr [4 i32])\n\
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(defn main [] i32\n\
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\ (set (at arr 0) 1)\n\
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\ (let [i 5] (print (at arr i)) (println \"\"))\n\
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\ 0)\n";
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(* Shift by the full width of the type: undefined in C, poison in LLVM,
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and invisible to UBSan here because nothing emitted a check for it. If
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this ever starts reporting, the note above is stale. *)
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control ~expect_report:false "flan-san-ctl-shift"
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~why:"UBSan has started seeing Flan code, which contradicts what this \
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file and Build.opts both say it reaches. Good news; rewrite them."
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"(defn main [] i32\n\
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\ (let [x 1] (let [n 32] (print (<< x n)) (println \"\")))\n\
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\ 0)\n";
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(* A regression case, and the one defect this exercise found: a slice's
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length is signed, (slice s 2 1) is -1, and flan_bytes_to_i64 cast that
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to size_t before comparing it against its buffer — so the memcpy copied
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63 bytes out of whatever the slice pointed at. Every other (ptr, len)
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entry point in the runtime already guarded the negative case; these two
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were the exceptions. A checked build traps on the reversed slice long
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before this, which is why it needs an unchecked build to show. *)
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control ~expect_report:false ~args:[ "2" ] "flan-san-ctl-negslice"
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~why:"flan_bytes_to_i64 or flan_bytes_to_f64 is reading off the end of \
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a negative-length slice again — see clamp_len in flan_rt.c."
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|
"(defn main [args [string]] i32\n\
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\ (let [s (bytes \"42\")\n\
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|
\ n (i32 (bytes->i64 (bytes (at args 1))))]\n\
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|
\ (print (bytes->i64 (slice s n 1)))\n\
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|
\ (println \"\"))\n\
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|
\ 0)\n";
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|
sweep ~checks:true "checked";
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|
dyn_sweep ();
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|
unchecked_controls ();
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|
if !failures = 0 then print_endline "sanitizer sweep: clean"
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|
else Printf.printf "%d sanitizer failure(s)\n" !failures;
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|
exit (if !failures = 0 then 0 else 1)
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|
| _ ->
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|
print_endline "no clang on PATH; sanitizer sweep skipped"
|