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aefcf2f4b5
Pull kernel lockdown mode from James Morris:
"This is the latest iteration of the kernel lockdown patchset, from
Matthew Garrett, David Howells and others.
From the original description:
This patchset introduces an optional kernel lockdown feature,
intended to strengthen the boundary between UID 0 and the kernel.
When enabled, various pieces of kernel functionality are restricted.
Applications that rely on low-level access to either hardware or the
kernel may cease working as a result - therefore this should not be
enabled without appropriate evaluation beforehand.
The majority of mainstream distributions have been carrying variants
of this patchset for many years now, so there's value in providing a
doesn't meet every distribution requirement, but gets us much closer
to not requiring external patches.
There are two major changes since this was last proposed for mainline:
- Separating lockdown from EFI secure boot. Background discussion is
covered here: https://lwn.net/Articles/751061/
- Implementation as an LSM, with a default stackable lockdown LSM
module. This allows the lockdown feature to be policy-driven,
rather than encoding an implicit policy within the mechanism.
The new locked_down LSM hook is provided to allow LSMs to make a
policy decision around whether kernel functionality that would allow
tampering with or examining the runtime state of the kernel should be
permitted.
The included lockdown LSM provides an implementation with a simple
policy intended for general purpose use. This policy provides a coarse
level of granularity, controllable via the kernel command line:
lockdown={integrity|confidentiality}
Enable the kernel lockdown feature. If set to integrity, kernel features
that allow userland to modify the running kernel are disabled. If set to
confidentiality, kernel features that allow userland to extract
confidential information from the kernel are also disabled.
This may also be controlled via /sys/kernel/security/lockdown and
overriden by kernel configuration.
New or existing LSMs may implement finer-grained controls of the
lockdown features. Refer to the lockdown_reason documentation in
include/linux/security.h for details.
The lockdown feature has had signficant design feedback and review
across many subsystems. This code has been in linux-next for some
weeks, with a few fixes applied along the way.
Stephen Rothwell noted that commit 9d1f8be5cf ("bpf: Restrict bpf
when kernel lockdown is in confidentiality mode") is missing a
Signed-off-by from its author. Matthew responded that he is providing
this under category (c) of the DCO"
* 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: (31 commits)
kexec: Fix file verification on S390
security: constify some arrays in lockdown LSM
lockdown: Print current->comm in restriction messages
efi: Restrict efivar_ssdt_load when the kernel is locked down
tracefs: Restrict tracefs when the kernel is locked down
debugfs: Restrict debugfs when the kernel is locked down
kexec: Allow kexec_file() with appropriate IMA policy when locked down
lockdown: Lock down perf when in confidentiality mode
bpf: Restrict bpf when kernel lockdown is in confidentiality mode
lockdown: Lock down tracing and perf kprobes when in confidentiality mode
lockdown: Lock down /proc/kcore
x86/mmiotrace: Lock down the testmmiotrace module
lockdown: Lock down module params that specify hardware parameters (eg. ioport)
lockdown: Lock down TIOCSSERIAL
lockdown: Prohibit PCMCIA CIS storage when the kernel is locked down
acpi: Disable ACPI table override if the kernel is locked down
acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down
ACPI: Limit access to custom_method when the kernel is locked down
x86/msr: Restrict MSR access when the kernel is locked down
x86: Lock down IO port access when the kernel is locked down
...
97 lines
2.4 KiB
C
97 lines
2.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Copyright (C) 2018 IBM Corporation
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*/
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#include <linux/efi.h>
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#include <linux/module.h>
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#include <linux/ima.h>
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extern struct boot_params boot_params;
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static enum efi_secureboot_mode get_sb_mode(void)
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{
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efi_char16_t efi_SecureBoot_name[] = L"SecureBoot";
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efi_char16_t efi_SetupMode_name[] = L"SecureBoot";
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efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
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efi_status_t status;
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unsigned long size;
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u8 secboot, setupmode;
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size = sizeof(secboot);
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if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
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pr_info("ima: secureboot mode unknown, no efi\n");
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return efi_secureboot_mode_unknown;
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}
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/* Get variable contents into buffer */
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status = efi.get_variable(efi_SecureBoot_name, &efi_variable_guid,
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NULL, &size, &secboot);
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if (status == EFI_NOT_FOUND) {
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pr_info("ima: secureboot mode disabled\n");
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return efi_secureboot_mode_disabled;
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}
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if (status != EFI_SUCCESS) {
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pr_info("ima: secureboot mode unknown\n");
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return efi_secureboot_mode_unknown;
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}
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size = sizeof(setupmode);
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status = efi.get_variable(efi_SetupMode_name, &efi_variable_guid,
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NULL, &size, &setupmode);
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if (status != EFI_SUCCESS) /* ignore unknown SetupMode */
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setupmode = 0;
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if (secboot == 0 || setupmode == 1) {
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pr_info("ima: secureboot mode disabled\n");
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return efi_secureboot_mode_disabled;
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}
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pr_info("ima: secureboot mode enabled\n");
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return efi_secureboot_mode_enabled;
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}
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bool arch_ima_get_secureboot(void)
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{
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static enum efi_secureboot_mode sb_mode;
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static bool initialized;
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if (!initialized && efi_enabled(EFI_BOOT)) {
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sb_mode = boot_params.secure_boot;
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if (sb_mode == efi_secureboot_mode_unset)
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sb_mode = get_sb_mode();
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initialized = true;
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}
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if (sb_mode == efi_secureboot_mode_enabled)
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return true;
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else
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return false;
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}
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/* secureboot arch rules */
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static const char * const sb_arch_rules[] = {
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#if !IS_ENABLED(CONFIG_KEXEC_SIG)
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"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
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#endif /* CONFIG_KEXEC_SIG */
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"measure func=KEXEC_KERNEL_CHECK",
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#if !IS_ENABLED(CONFIG_MODULE_SIG)
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"appraise func=MODULE_CHECK appraise_type=imasig",
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#endif
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"measure func=MODULE_CHECK",
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NULL
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};
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const char * const *arch_get_ima_policy(void)
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{
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if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot()) {
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if (IS_ENABLED(CONFIG_MODULE_SIG))
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set_module_sig_enforced();
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return sb_arch_rules;
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}
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return NULL;
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}
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