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Date:   Thu, 18 Jul 2019 12:43:52 -0700
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Subject: [PATCH V36 06/29] kexec_load: Disable at runtime if the kernel is
 locked down
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
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Sender: linux-kernel-owner@vger.kernel.org
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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",
 };
-- 
2.22.0.510.g264f2c817a-goog