From nobody Sat Feb 7 19:41:24 2026 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.18]) (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 2E201393 for ; Fri, 9 Feb 2024 01:12:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707441140; cv=none; b=i2uR2hOy8CUZjzbgs5Az+D2TCPba4Q6ECGOfQNLW1tO4EIMsiYZr+qvyowQqpdzK+fpMNWhydCUTSnyGFZmNiDDmEYSdH4P9FrxJqaxYV03KFA7cj/FQlKcJgJSR9lJJ+ZneYgIMWDyMK9xiW7Ub3G7JeyVBpceaNrJ4ahEjX8Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707441140; c=relaxed/simple; bh=5ugxdFzfPJ/RIttI+/1rpcWJPZsgRn96cfp/VI68TFE=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=qvnp8685wL5V71/3C/fldoD9yWeOpA2QLR87J2M7VN/akzaryLnuN+mJIOvk6BtGrF8UG9JaEe8PqqhJPfMI4C7GIitCbQBJNnzXFYUNuoSIO8uUt3/uX78PO+zVAjOGhZBUSQ6Wcz5Et9F6mpAujpNFInqoFzw7q3iCFL6ppSg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=b5+jdlHN; arc=none smtp.client-ip=192.198.163.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="b5+jdlHN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1707441138; x=1738977138; h=date:from:to:cc:subject:message-id:mime-version; bh=5ugxdFzfPJ/RIttI+/1rpcWJPZsgRn96cfp/VI68TFE=; b=b5+jdlHNp2Dd/30CLwD21Zc7ydX8xdxNI8ir5rsK6as3U2adraheloqY B4TMLKansqgjTSzsrkzgjOfhRdAxJI61HAaXVIRM3F2Twks37CZxKZiht r2FxK4lGgOok6KkIlY5e+uom449uSuEkWmRjVh6E/PHIwbzsv0UEEk2m2 d1/D0aKPPazjo5nc8qyMyEsS67O78CL1GeQIj19sM3DLNhy9Dp4ieOGIf ggOUfsBGrdOdxghIX7sFQWGgCBceAScX3S0k/jn3KQVZJeNZaxo6VyFyw fbj/iDa1DbBeDicgdNUmx/6QhSCG3XVbCOc8BIEvfNjaYbwgYm87yaVX9 Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10978"; a="1233522" X-IronPort-AV: E=Sophos;i="6.05,255,1701158400"; d="scan'208";a="1233522" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Feb 2024 17:12:17 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,255,1701158400"; d="scan'208";a="39256673" Received: from rgalhena-mobl.amr.corp.intel.com (HELO desk) ([10.209.25.138]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Feb 2024 17:12:16 -0800 Date: Thu, 8 Feb 2024 17:12:15 -0800 From: Pawan Gupta To: Thomas Gleixner , Borislav Petkov , Peter Zijlstra , Josh Poimboeuf , Ingo Molnar , Dave Hansen , x86@kernel.org, "H. Peter Anvin" Cc: Daniel Sneddon , antonio.gomez.iglesias@linux.intel.com, alyssa.milburn@linux.intel.com, andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org, Alyssa Milburn Subject: [PATCH] x86/bugs: Default retbleed to =stuff when retpoline is auto enabled Message-ID: <20240208-retbleed-auto-stuff-v1-1-6f12e513868f@linux.intel.com> X-B4-Tracking: v=1; b=H4sIAIAzxWUC/x3MwQ5FMBBG4VeRWd9JRpHgVeQuir9MIkhbIhHvr rH8FufcFOAVgdrsJo9Tg25rQv7LaJjtOoF1TCYjphQjNXvEfgFGtkfcOMTDOa4KiLNNXkgFSuX u4fT6rt3/eV6jurabZQAAAA== X-Mailer: b4 0.12.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" On Intel systems when retpoline mitigation is enabled for spectre-v2, retbleed=3Dauto does not enable RSB stuffing. This may make the system vulnerable to retbleed. Retpoline is not the default mitigation when IBRS is present, but in virtualized cases a VMM can hide IBRS from guests, resulting in guest deploying retpoline by default. On Intel systems, when spectre_v2 and retbleed mitigations are in auto mode, and retpoline is enabled, deploy Call Depth Tracking and RSB stuffing i.e. retbleed=3Dstuff mitigation. For AMD/Hygon auto mode already selects the appropriate mitigation. Reported-by: Alyssa Milburn Signed-off-by: Pawan Gupta --- arch/x86/kernel/cpu/bugs.c | 39 ++++++++++++++++++++++++--------------- 1 file changed, 24 insertions(+), 15 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index bb0ab8466b91..55d94b71af18 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -50,6 +50,8 @@ static void __init l1d_flush_select_mitigation(void); static void __init srso_select_mitigation(void); static void __init gds_select_mitigation(void); =20 +static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void= ); + /* The base value of the SPEC_CTRL MSR without task-specific bits set */ u64 x86_spec_ctrl_base; EXPORT_SYMBOL_GPL(x86_spec_ctrl_base); @@ -892,6 +894,20 @@ static int __init nospectre_v1_cmdline(char *str) } early_param("nospectre_v1", nospectre_v1_cmdline); =20 +/* The kernel command line selection for spectre v2 */ +enum spectre_v2_mitigation_cmd { + SPECTRE_V2_CMD_NONE, + SPECTRE_V2_CMD_AUTO, + SPECTRE_V2_CMD_FORCE, + SPECTRE_V2_CMD_RETPOLINE, + SPECTRE_V2_CMD_RETPOLINE_GENERIC, + SPECTRE_V2_CMD_RETPOLINE_LFENCE, + SPECTRE_V2_CMD_EIBRS, + SPECTRE_V2_CMD_EIBRS_RETPOLINE, + SPECTRE_V2_CMD_EIBRS_LFENCE, + SPECTRE_V2_CMD_IBRS, +}; + enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =3D SPECTRE_= V2_NONE; =20 #undef pr_fmt @@ -1025,10 +1041,17 @@ static void __init retbleed_select_mitigation(void) retbleed_mitigation =3D RETBLEED_MITIGATION_UNRET; else if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY) && boot_cpu_has(X86_FEATURE_= IBPB)) retbleed_mitigation =3D RETBLEED_MITIGATION_IBPB; + } else if (boot_cpu_data.x86_vendor =3D=3D X86_VENDOR_INTEL && + spectre_v2_parse_cmdline() =3D=3D SPECTRE_V2_CMD_AUTO && + spectre_v2_enabled =3D=3D SPECTRE_V2_RETPOLINE) { + if (IS_ENABLED(CONFIG_CALL_DEPTH_TRACKING)) + retbleed_mitigation =3D RETBLEED_MITIGATION_STUFF; + else + pr_err("WARNING: Retpoline enabled, but kernel not compiled with CALL_= DEPTH_TRACKING.\n"); } =20 /* - * The Intel mitigation (IBRS or eIBRS) was already selected in + * If Intel mitigation (IBRS or eIBRS) was already selected in * spectre_v2_select_mitigation(). 'retbleed_mitigation' will * be set accordingly below. */ @@ -1157,20 +1180,6 @@ static inline bool match_option(const char *arg, int= arglen, const char *opt) return len =3D=3D arglen && !strncmp(arg, opt, len); } =20 -/* The kernel command line selection for spectre v2 */ -enum spectre_v2_mitigation_cmd { - SPECTRE_V2_CMD_NONE, - SPECTRE_V2_CMD_AUTO, - SPECTRE_V2_CMD_FORCE, - SPECTRE_V2_CMD_RETPOLINE, - SPECTRE_V2_CMD_RETPOLINE_GENERIC, - SPECTRE_V2_CMD_RETPOLINE_LFENCE, - SPECTRE_V2_CMD_EIBRS, - SPECTRE_V2_CMD_EIBRS_RETPOLINE, - SPECTRE_V2_CMD_EIBRS_LFENCE, - SPECTRE_V2_CMD_IBRS, -}; - enum spectre_v2_user_cmd { SPECTRE_V2_USER_CMD_NONE, SPECTRE_V2_USER_CMD_AUTO, --- base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478 change-id: 20240208-retbleed-auto-stuff-53e0fa91305e Best regards, --=20 Thanks, Pawan