From nobody Fri Oct 3 07:39:28 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 47467227B95; Thu, 4 Sep 2025 03:46:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756957617; cv=none; b=gMdU/neYrJ34f1Y7/XKLr6/z5bi3v4krMLvwRTvqUeeWDQPkNXJyPosx+DO0x++cuqp4zwGo8mFw3d4VOT3uHrAjtdB2yZuw4fEUeADXm7QK5JgmuU5ttyxK7cdNx1xdtpqliWODVcSh65o/Aa11X9k4xlH3x5f1EMfC2VVKEsE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756957617; c=relaxed/simple; bh=fAYAUBGJzo8b71uhoB5b/MGQo+Cci4aVf5GCY6U9+Og=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=rw453e6whmIuS3oQNsnnT4ENy9MSNEoe2TKetTLZst2HthssYaONPlXhD+hIwpNrNQF14hH9nyA8Z9YwTtpCz6Yv9TB2G0QsNhpPUOBYLApoTMdlvQsCeyVOa2BZzTyMS6qZIIRIXJNMMh698M4h2ZWVn6/PoJ2zwe5qkOsfAr8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MQ1wii6x; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MQ1wii6x" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC035C4CEF9; Thu, 4 Sep 2025 03:46:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756957616; bh=fAYAUBGJzo8b71uhoB5b/MGQo+Cci4aVf5GCY6U9+Og=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MQ1wii6xQtLMVMyBk31+A/kBaQZrsWcYyRslt3wRiqrIgJwSD/vMPaXxjHvlXQ70q woTlgLahuOMaNldVXWLhxv2VMw2yg/a+mZCFThs/9eKCSPvWWRfFrEOFKQtQiGkT8z sktrp+AQAN1Pdu004OOJa/HLhNZSkHtv9w1bXPvGVrCtnMgPiKUnBGz3Xmyr8+3RmF 5LJR8DZfAIL+HlnYDABwGlNeuiP5F6UhvbusAD7TJS/CpsANxCtcciMaUcy11PtthN xsT3PWpg8CJApz2ug6Z9Qhf11n7EK75u9A1C8Y5jXxW5j90q3cig/joCyV0pxelZI3 12GobLSRdOnrg== From: Kees Cook To: Peter Zijlstra Cc: Kees Cook , Nathan Chancellor , Vegard Nossum , Miguel Ojeda , Linus Walleij , Jeff Johnson , Randy Dunlap , David Woodhouse , "Russell King (Oracle)" , Nick Desaulniers , Bill Wendling , Justin Stitt , Marco Elver , Przemek Kitszel , Ramon de C Valle , Jonathan Corbet , "Paul E. McKenney" , Nicolas Schier , Masahiro Yamada , Arnd Bergmann , Krzysztof Kozlowski , Sami Tolvanen , Mark Rutland , linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2 5/9] x86/cfi: Add "debug" option to "cfi=" bootparam Date: Wed, 3 Sep 2025 20:46:44 -0700 Message-Id: <20250904034656.3670313-5-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250904033217.it.414-kees@kernel.org> References: <20250904033217.it.414-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4249; i=kees@kernel.org; h=from:subject; bh=fAYAUBGJzo8b71uhoB5b/MGQo+Cci4aVf5GCY6U9+Og=; b=owGbwMvMwCVmps19z/KJym7G02pJDBk7OYuNvPgOPD79OO+JnXXRp6Xu8nwx71xY93EVlCf3x 6bxXNvQUcrCIMbFICumyBJk5x7n4vG2Pdx9riLMHFYmkCEMXJwCMJGpYgy/2VR2/91myqOcFp/c 6yV1dvuyNcnb3k/h3Mb8pmgBG98MTYZ/Vv2fVK7qNr275O/OvuS9daCF9u2IlUJSrJ9OcjL0z+V mAwA= X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add "debug" option for "cfi=3D" bootparam to get details on early CFI initialization steps so future Kees can find breakage easier. Signed-off-by: Kees Cook --- Cc: Peter Zijlstra --- .../admin-guide/kernel-parameters.txt | 1 + arch/x86/kernel/alternative.c | 23 +++++++++++++++++++ 2 files changed, 24 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 8bbffbb334ab..c8337d0e6ba3 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -624,6 +624,7 @@ bhi: Enable register poisoning to stop speculation across FineIBT. (Disabled by default.) warn: Do not enforce CFI checking: warn only. + debug: Report CFI initialization details. =20 cgroup_disable=3D [KNL] Disable a particular controller or optional featu= re Format: {name of the controller(s) or feature(s) to disable} diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index d8f4ac95b4df..b311e31a9056 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1177,6 +1177,7 @@ void __init_or_module apply_seal_endbr(s32 *start, s3= 2 *end) { } #endif =20 enum cfi_mode cfi_mode __ro_after_init =3D __CFI_DEFAULT; +static bool cfi_debug __ro_after_init; =20 #ifdef CONFIG_FINEIBT_BHI bool cfi_bhi __ro_after_init =3D false; @@ -1259,6 +1260,8 @@ static __init int cfi_parse_cmdline(char *str) } else if (!strcmp(str, "off")) { cfi_mode =3D CFI_OFF; cfi_rand =3D false; + } else if (!strcmp(str, "debug")) { + cfi_debug =3D true; } else if (!strcmp(str, "kcfi")) { cfi_mode =3D CFI_KCFI; } else if (!strcmp(str, "fineibt")) { @@ -1734,6 +1737,8 @@ static void __apply_fineibt(s32 *start_retpoline, s32= *end_retpoline, * rewrite them. This disables all CFI. If this succeeds but any of the * later stages fails, we're without CFI. */ + if (cfi_debug) + pr_info("CFI: disabling all indirect call checking\n"); ret =3D cfi_disable_callers(start_retpoline, end_retpoline); if (ret) goto err; @@ -1744,14 +1749,23 @@ static void __apply_fineibt(s32 *start_retpoline, s= 32 *end_retpoline, cfi_bpf_hash =3D cfi_rehash(cfi_bpf_hash); cfi_bpf_subprog_hash =3D cfi_rehash(cfi_bpf_subprog_hash); } + if (cfi_debug) + pr_info("CFI: cfi_seed: 0x%08x\n", cfi_seed); =20 + if (cfi_debug) + pr_info("CFI: rehashing all preambles\n"); ret =3D cfi_rand_preamble(start_cfi, end_cfi); if (ret) goto err; =20 + if (cfi_debug) + pr_info("CFI: rehashing all indirect calls\n"); ret =3D cfi_rand_callers(start_retpoline, end_retpoline); if (ret) goto err; + } else { + if (cfi_debug) + pr_info("CFI: rehashing disabled\n"); } =20 switch (cfi_mode) { @@ -1761,6 +1775,8 @@ static void __apply_fineibt(s32 *start_retpoline, s32= *end_retpoline, return; =20 case CFI_KCFI: + if (cfi_debug) + pr_info("CFI: enabling all indirect call checking\n"); ret =3D cfi_enable_callers(start_retpoline, end_retpoline); if (ret) goto err; @@ -1771,17 +1787,23 @@ static void __apply_fineibt(s32 *start_retpoline, s= 32 *end_retpoline, return; =20 case CFI_FINEIBT: + if (cfi_debug) + pr_info("CFI: adding FineIBT to all preambles\n"); /* place the FineIBT preamble at func()-16 */ ret =3D cfi_rewrite_preamble(start_cfi, end_cfi); if (ret) goto err; =20 /* rewrite the callers to target func()-16 */ + if (cfi_debug) + pr_info("CFI: rewriting indirect call sites to use FineIBT\n"); ret =3D cfi_rewrite_callers(start_retpoline, end_retpoline); if (ret) goto err; =20 /* now that nobody targets func()+0, remove ENDBR there */ + if (cfi_debug) + pr_info("CFI: removing old endbr insns\n"); cfi_rewrite_endbr(start_cfi, end_cfi); =20 if (builtin) { @@ -2324,6 +2346,7 @@ void __init alternative_instructions(void) =20 __apply_fineibt(__retpoline_sites, __retpoline_sites_end, __cfi_sites, __cfi_sites_end, true); + cfi_debug =3D false; =20 /* * Rewrite the retpolines, must be done before alternatives since --=20 2.34.1