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From: Matthew Garrett <matthewgarrett@google.com>
To: jmorris@namei.org
Cc: linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
	Matthew Garrett <mjg59@srcf.ucam.org>,
	David Howells <dhowells@redhat.com>,
	Matthew Garrett <mjg59@google.com>,
	Dave Young <dyoung@redhat.com>, Kees Cook <keescook@chromium.org>,
	kexec@lists.infradead.org
Subject: [PATCH V38 06/29] kexec_load: Disable at runtime if the kernel is locked down
Date: Wed,  7 Aug 2019 17:06:58 -0700
Message-ID: <20190808000721.124691-7-matthewgarrett@google.com> (raw)
In-Reply-To: <20190808000721.124691-1-matthewgarrett@google.com>

From: Matthew Garrett <mjg59@srcf.ucam.org>

The kexec_load() syscall permits the loading and execution of arbitrary
code in ring 0, which is something that lock-down is meant to prevent. It
makes sense to disable kexec_load() in this situation.

This does not affect kexec_file_load() syscall which can check for a
signature on the image to be booted.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Acked-by: Dave Young <dyoung@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
cc: kexec@lists.infradead.org
---
 include/linux/security.h     | 1 +
 kernel/kexec.c               | 8 ++++++++
 security/lockdown/lockdown.c | 1 +
 3 files changed, 10 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 9458152601b5..69c5de539e9a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -105,6 +105,7 @@ enum lockdown_reason {
 	LOCKDOWN_NONE,
 	LOCKDOWN_MODULE_SIGNATURE,
 	LOCKDOWN_DEV_MEM,
+	LOCKDOWN_KEXEC,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 1b018f1a6e0d..bc933c0db9bf 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -205,6 +205,14 @@ static inline int kexec_load_check(unsigned long nr_segments,
 	if (result < 0)
 		return result;
 
+	/*
+	 * kexec can be used to circumvent module loading restrictions, so
+	 * prevent loading in that case
+	 */
+	result = security_locked_down(LOCKDOWN_KEXEC);
+	if (result)
+		return result;
+
 	/*
 	 * Verify we have a legal set of flags
 	 * This leaves us room for future extensions.
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index d2ef29d9f0b2..6f302c156bc8 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -20,6 +20,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_NONE] = "none",
 	[LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
 	[LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port",
+	[LOCKDOWN_KEXEC] = "kexec of unsigned images",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
-- 
2.22.0.770.g0f2c4a37fd-goog


  parent reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-08  0:06 [PATCH V38 00/29] security: Add support for locking down the kernel Matthew Garrett
2019-08-08  0:06 ` [PATCH V38 01/29] security: Support early LSMs Matthew Garrett
2019-08-08  0:06 ` [PATCH V38 02/29] security: Add a "locked down" LSM hook Matthew Garrett
2019-08-08  0:06 ` [PATCH V38 03/29] security: Add a static lockdown policy LSM Matthew Garrett
2019-08-08  0:06 ` [PATCH V38 04/29] Enforce module signatures if the kernel is locked down Matthew Garrett
2019-08-08  0:06 ` [PATCH V38 05/29] Restrict /dev/{mem,kmem,port} when " Matthew Garrett
2019-08-08  0:06 ` Matthew Garrett [this message]
2019-08-08  0:06 ` [PATCH V38 07/29] Copy secure_boot flag in boot params across kexec reboot Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 08/29] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 09/29] kexec_file: Restrict at runtime if the kernel is locked down Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 10/29] hibernate: Disable when " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 11/29] PCI: Lock down BAR access " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 12/29] x86: Lock down IO port " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 13/29] x86/msr: Restrict MSR " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 14/29] ACPI: Limit access to custom_method " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 15/29] acpi: Ignore acpi_rsdp kernel param when the kernel has been " Matthew Garrett
2019-08-14  2:51   ` Dave Young
2019-08-14  7:26   ` Borislav Petkov
2019-08-14 17:14     ` Matthew Garrett
2019-08-14 17:47       ` Borislav Petkov
2019-08-14 18:02         ` Matthew Garrett
2019-08-14  7:28   ` Borislav Petkov
2019-08-08  0:07 ` [PATCH V38 16/29] acpi: Disable ACPI table override if the kernel is " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 17/29] Prohibit PCMCIA CIS storage when " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 18/29] Lock down TIOCSSERIAL Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 19/29] Lock down module params that specify hardware parameters (eg. ioport) Matthew Garrett
2019-08-08 11:12   ` Jessica Yu
2019-08-08 16:33     ` James Morris
2019-08-09 20:58     ` [PATCH V39] " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 20/29] x86/mmiotrace: Lock down the testmmiotrace module Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 21/29] Lock down /proc/kcore Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 22/29] Lock down tracing and perf kprobes when in confidentiality mode Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 23/29] bpf: Restrict bpf when kernel lockdown is " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 24/29] Lock down perf when " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 25/29] kexec: Allow kexec_file() with appropriate IMA policy when locked down Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 26/29] debugfs: Restrict debugfs when the kernel is " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 27/29] tracefs: Restrict tracefs " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 28/29] efi: Restrict efivar_ssdt_load " Matthew Garrett
2019-08-08  0:07 ` [PATCH V38 29/29] lockdown: Print current->comm in restriction messages Matthew Garrett
2019-08-10  6:08 ` [PATCH V38 00/29] security: Add support for locking down the kernel James Morris
2019-08-12 17:06   ` Matthew Garrett
2019-08-12 17:39     ` James Morris
2019-08-12 22:29       ` James Morris

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