Missing Linux Kernel mitigations for 'Cross-Thread Return Address Predictions' hardware vulnerability (AMD-SB-1045)

# SPDX-FileCopyrightText: 2023 Greenbone AG
# Some text descriptions might be excerpted from (a) referenced
# source(s), and are Copyright (C) by the respective right holder(s).
#
# SPDX-License-Identifier: GPL-2.0-only

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.104689");
  script_version("2024-03-26T05:06:00+0000");
  script_cve_id("CVE-2022-27672");
  script_tag(name:"last_modification", value:"2024-03-26 05:06:00 +0000 (Tue, 26 Mar 2024)");
  script_tag(name:"creation_date", value:"2023-04-18 09:39:40 +0000 (Tue, 18 Apr 2023)");
  script_tag(name:"cvss_base", value:"3.8");
  script_tag(name:"cvss_base_vector", value:"AV:L/AC:H/Au:S/C:C/I:N/A:N");
  script_tag(name:"severity_vector", value:"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N");
  script_tag(name:"severity_origin", value:"NVD");
  script_tag(name:"severity_date", value:"2023-03-10 01:55:00 +0000 (Fri, 10 Mar 2023)");
  script_name("Missing Linux Kernel mitigations for 'Cross-Thread Return Address Predictions' hardware vulnerability (AMD-SB-1045)");
  script_category(ACT_GATHER_INFO);
  script_copyright("Copyright (C) 2023 Greenbone AG");
  script_family("General");
  script_dependencies("gb_hw_vuln_linux_kernel_mitigation_detect.nasl", "gb_gather_hardware_info_ssh_login.nasl");
  script_mandatory_keys("ssh/hw_vulns/kernel_mitigations/missing_or_vulnerable");

  script_xref(name:"URL", value:"https://docs.kernel.org/admin-guide/hw-vuln/cross-thread-rsb.html");
  script_xref(name:"URL", value:"https://www.amd.com/en/resources/product-security/bulletin/AMD-SB-1045.html");

  script_tag(name:"summary", value:"The remote host is missing one or more known mitigation(s) on
  Linux Kernel side for the referenced 'Cross-Thread Return Address Predictions' hardware
  vulnerability.");

  # nb: See e.g. https://lore.kernel.org/lkml/[email protected]/T/ for
  # the origin of the additional note:
  # > The Spectre v2 mitigations cover the Linux kernel, as it fills the RSB when context switching
  # > to the idle thread.
  script_tag(name:"vuldetect", value:"Checks previous gathered information on the mitigation status
  reported by the Linux Kernel.

  Note: The detection is happening based on the existence of Spectre v2 mitigations because these
  will fill the RSB on context switch and mitigate this flaw as well.");

  script_tag(name:"affected", value:"Various AMD and Hygon CPUs. Please see the references for the
  full list of affected AMD CPUs.");

  script_tag(name:"solution", value:"The following solutions exist:

  - Update to a more recent Linux Kernel to receive mitigations on Kernel level and info about
  the mitigation status from it

  - Enable the mitigation(s) in the Linux Kernel (might be disabled depending on the configuration)

  Additional possible mitigations (if provided by the vendor) are to:

  - install a Microcode update

  - update the BIOS of the Mainboard

  Note: Please create an override for this result if one of the following applies:

  - the sysfs file is not available but other mitigations like a Microcode update is already in
  place

  - the sysfs file is not available but the CPU of the host is not affected

  - the reporting of the Linux Kernel is not correct (this is out of the control of this VT)");

  script_tag(name:"qod", value:"80"); # nb: None of the existing QoD types are matching here
  script_tag(name:"solution_type", value:"VendorFix");

  exit(0);
}

include("misc_func.inc");
include("list_array_func.inc");
include("host_details.inc");

if( ! get_kb_item( "ssh/hw_vulns/kernel_mitigations/missing_or_vulnerable" ) )
  exit( 99 );

covered_vuln = "spectre_v2";

if( ! mitigation_status = get_kb_item( "ssh/hw_vulns/kernel_mitigations/missing_or_vulnerable/" + covered_vuln ) )
  exit( 99 );

# nb: Only AMD CPUs affected (Also Hygon but we currently don't know how this vendor is reported
# currently...). But we're only checking this if the sysfs file is missing and otherwise trust the
# Linux kernel (at least for now) that it reports the CPU as "Not affected" correctly.
if( "sysfs file missing (" >< mitigation_status ) {
  cpu_vendor_id = get_kb_item( "ssh/login/cpu_vendor_id" );
  if( cpu_vendor_id && "AuthenticAMD" >!< cpu_vendor_id )
    exit( 99 );
}

report = 'The Linux Kernel on the remote host is missing the mitigation for the "' + covered_vuln + '" (includes mitigation for the Cross-Thread Return Address Predictions flaw) hardware vulnerability as reported by the sysfs interface:\n\n';

path = "/sys/devices/system/cpu/vulnerabilities/" + covered_vuln;
info[path] = mitigation_status;

# Store link between gb_hw_vuln_linux_kernel_mitigation_detect.nasl and this VT.
# nb: We don't use the host_details.inc functions in both so we need to call this directly.
register_host_detail( name:"detected_by", value:"1.3.6.1.4.1.25623.1.0.108765" ); # gb_hw_vuln_linux_kernel_mitigation_detect.nasl
register_host_detail( name:"detected_at", value:"general/tcp" ); # gb_hw_vuln_linux_kernel_mitigation_detect.nasl is using port:0

report += text_format_table( array:info, sep:" | ", columnheader:make_list( "sysfs file checked", "Linux Kernel status (SSH response)" ) );
report += '\n\nNote: The detection is happening based on the existence of Spectre v2 mitigations because these will fill the RSB on context switch and mitigate this flaw as well.';
report += '\n\nNotes on the "Linux Kernel status (SSH response)" column:';
report += '\n- sysfs file missing: The sysfs interface is available but the sysfs file for this specific vulnerability is missing. This means the current Linux Kernel doesn\'t know this vulnerability yet. Based on this it is assumed that it doesn\'t provide any mitigation and that the target system is vulnerable.';
report += '\n- Strings including "Mitigation:", "Not affected" or "Vulnerable" are reported directly by the Linux Kernel.';
report += '\n- All other strings are responses to various SSH commands.';

security_message( port:0, data:report );
exit( 0 );