From nobody Fri Sep 25 00:04:51 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0AF9A382F1F; Fri, 18 Sep 2026 10:14:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789726499; cv=none; b=unzt11G/4EeZbg5e981XanSR5ZfisZwWAI6TPK1cybH7IbqBb9UcOrVIiFJ8OBqwTrBhOoznd3mlrDpHVGdwp72UoUtb9WWLQtBtycn/W4X5XdRq4GbTez3lzZvKIX90X7Z7s6EBz4xXEc1Mg+WuVpsxmMwhM3xwNEuPz/9xfrg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789726499; c=relaxed/simple; bh=LId6u/F/PUqTMc35M7moZQbKP/J6zvIMG1vD2TkA02Y=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=rooCm8RLouyPR5mH46uwIacTjuPox100helx1iP062SLPRHayEk63XgCv6+7c4LwyrHvwsaoud5Gg5ePakZeURGDiEmpVANRRap4AMSQGA/37HuDydZbpKso2G+bIDWBYt4AeEir2S84Rj9FezlwZntXZXHjtIxM9pQlsIJ2Yl8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=aPxrgfwA; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=kb1IZhos; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="aPxrgfwA"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="kb1IZhos" Date: Fri, 18 Sep 2026 10:14:52 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1789726494; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+jhfe4XjFETZvJovCd94AA4v/uEElLKQQ61HRNA+TCQ=; b=aPxrgfwA+dCN+//YBJ9S2CMbNyx/y6FyeSwcI48ItURQ6w8KrfBtWsHLJd4YeGSol2hhM8 Xx86JulOAEQv3UuBxq39Xxl+ANCwpCf+Snqk4WXOYvDcOD+nmMR77bsZ/2wSYWCNL+2Qur SgD7OejN8bK+Q4YcdyfxTlMJAN9nDoNnHVpT4cpje+H0YuiB6bN7q966uICUYB9e4vCrwl mJeNQgKd2s/R0+KRttV9WJGG9rtZFMrOLvLzec3hEoJX5+n9dn7zAiEfWHu1Cjrurvxjwb xLleKALUJVvuN4phsnItxhc+Y70y8deL1xRs8ANhy3CxGNPSZBUaC67ASY9qJQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1789726494; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+jhfe4XjFETZvJovCd94AA4v/uEElLKQQ61HRNA+TCQ=; b=kb1IZhosEgJFEHzO5lNw2zduy8Qgu0HuGdkYVeopL0hBj0Fo2253HBZ+f7DVa6Tk5L4eDC bAb1Bi9ISNVMpLCA== From: "tip-bot2 for Song Liu" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: objtool/core] objtool/klp: Add test for UBSAN metadata in an unchanged function Cc: Song Liu , Josh Poimboeuf , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20260916184351.2720310-57-song@kernel.org> References: <20260916184351.2720310-57-song@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <178972649252.1720534.12858000319581110169.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the objtool/core branch of tip: Commit-ID: 3577ff3e09b738c9f92620b3254e859182794643 Gitweb: https://git.kernel.org/tip/3577ff3e09b738c9f92620b3254e85918= 2794643 Author: Song Liu AuthorDate: Wed, 16 Sep 2026 11:43:49 -07:00 Committer: Josh Poimboeuf CommitterDate: Wed, 16 Sep 2026 17:21:47 -07:00 objtool/klp: Add test for UBSAN metadata in an unchanged function Every instrumented operation gets a per-callsite metadata object in an anonymous data section -- .data..Lubsan_data and .data..Lubsan_type from GCC, .data..L__unnamed_ from Clang -- whose names are compiler-generated and mean nothing across a rebuild. is_uncorrelated_section() exists so klp diff does not try to pair them up, and nothing tested it. The failure it prevents is a false positive, which is the direction this suite has least coverage of. Metadata belonging to a function nobody touched compares as different and drags that function into the patch. That is not a build failure: it is a larger livepatch than intended, pulling in dependencies with it, and every extra function is one more that can fail to correlate or to apply. The fixture is built with -fsanitize=3Dshift, which both compilers instrument; neither emits a bounds check for an index it can prove in range. One function changes, the other is byte-identical and carries instrumentation of its own, and the test asserts the second is left alone. Verified by removing each rule from is_uncorrelated_section() in turn, which splits neatly by toolchain: dropping the .data..Lubsan rule fails the test under gcc, dropping .data..L__unnamed_ fails it under clang. One test, two code paths, each checked by the compiler that reaches it. Assisted-by: Claude:claude-opus-4 Based-on-test-by: Joe Lawrence Assisted-by: Claude:claude-opus-5 Signed-off-by: Song Liu Link: https://patch.msgid.link/20260916184351.2720310-57-song@kernel.org Signed-off-by: Josh Poimboeuf --- tools/objtool/tests/generic/fixtures/ubsan_noise.c | 49 +++++++++++++- tools/objtool/tests/generic/test-ubsan-noise.sh | 48 +++++++++++++- 2 files changed, 97 insertions(+) create mode 100644 tools/objtool/tests/generic/fixtures/ubsan_noise.c create mode 100755 tools/objtool/tests/generic/test-ubsan-noise.sh diff --git a/tools/objtool/tests/generic/fixtures/ubsan_noise.c b/tools/obj= tool/tests/generic/fixtures/ubsan_noise.c new file mode 100644 index 0000000..bf59992 --- /dev/null +++ b/tools/objtool/tests/generic/fixtures/ubsan_noise.c @@ -0,0 +1,49 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * A translation unit built with UBSAN, where only one of two functions is + * patched. + * + * Every instrumented operation gets a per-callsite metadata object in an + * anonymous data section -- .data..Lubsan_data and .data..Lubsan_type from + * GCC, .data..L__unnamed_ from Clang -- and a call to a __ubsan_handle_* + * routine. The names are compiler-generated and carry no meaning across a + * rebuild, so klp diff has to treat those sections as uncorrelated rather= than + * pairing them up by name. + * + * untouched() is byte-identical in both builds and exists to catch the fa= lse + * positive: if the metadata were correlated by name, its shifts would look + * changed and it would be dragged into the patch. + * + * The shifts are what draw the instrumentation. A bounds check would do = as + * well but neither compiler emits one for an index it can prove in range. + */ + +static const char __modinfo[] + __attribute__((section(".modinfo"), used, aligned(1))) =3D "\0name=3Dvmli= nux"; + +int shift_by(int v, int n); + +int untouched(int v, int n) +{ + int s =3D 0; + + s +=3D v << (n & 31); + s +=3D v << ((n + 1) & 31); + s +=3D shift_by(v, n); + + return s; +} + +int touched(int v, int n) +{ + int s =3D 0; + + s +=3D v << (n & 31); +#ifdef PATCHED + s +=3D v << ((n + 3) & 31); +#else + s +=3D v << ((n + 2) & 31); +#endif + + return s; +} diff --git a/tools/objtool/tests/generic/test-ubsan-noise.sh b/tools/objtoo= l/tests/generic/test-ubsan-noise.sh new file mode 100755 index 0000000..b415eb1 --- /dev/null +++ b/tools/objtool/tests/generic/test-ubsan-noise.sh @@ -0,0 +1,48 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 +# +# UBSAN instrumentation in an unchanged function must not make it look cha= nged. +# +# Every instrumented operation gets a per-callsite metadata object in an +# anonymous data section -- .data..Lubsan_data and .data..Lubsan_type from= GCC, +# .data..L__unnamed_ from Clang -- whose names are compiler-generated and = mean +# nothing across a rebuild. is_uncorrelated_section() exists so klp diff = does +# not try to pair them up. +# +# Without that, the metadata belonging to a function nobody touched compar= es as +# different and drags the function into the patch. A livepatch which repl= aces +# functions the patch never changed is not a build failure: it is a larger +# patch than intended, taking its dependencies with it, and every extra +# function is one more that can fail to correlate or to apply. +# +# Covers the same ground as corpus/x86_64-ubsan/{ubsan-shift-noise, +# ubsan-metadata-data-section,gcc-ubsan-anonymous-data,ubsan-handler-cloni= ng} +# and corpus/x86_64-llvm-ubsan/{clang-ubsan-bounds-noise, +# clang-ubsan-handler-cloning} in Joe Lawrence's klp-build unit test corpu= s. + +. "$(dirname "$0")/../lib.sh" + +setup +build_pair ubsan_noise.c -fsanitize=3Dshift + +# The premise: this compiler really did instrument, and left its metadata = in an +# anonymous section. Without that the test is just test-basic again. +ubsan_sec=3D"$(in_sections orig.o | + grep -oE '\.data\.\.L(ubsan_data|__unnamed_)[A-Za-z0-9_.]*' | head -1)" +[ -n "$ubsan_sec" ] || + probe_skip "compiler emitted no anonymous UBSAN data section" +assert_input_symbol untouched + +run_diff + +# The changed function is patched, and the untouched one is left alone des= pite +# carrying instrumentation of its own. +assert_patched touched +assert_not_patched untouched + +# The handler the patched code calls has to come with it, or the clone cal= ls +# nothing when its check fires. +out_symbols | grep -q '__ubsan_handle_' || + fail "no __ubsan_handle_* reference in the patched output" + +pass "UBSAN metadata in an unchanged function does not drag it into the pa= tch"