linux-kernel - [PATCH 08/27] kexec_file: Restrict at runtime if the kernel is locked down

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Message-Id: <20190228231203.212359-8-matthewgarrett@google.com>
Date:   Thu, 28 Feb 2019 15:11:44 -0800
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com
Subject: [PATCH 08/27] kexec_file: Restrict at runtime if the kernel is locked down

From: Jiri Bohac <jbohac@...e.cz>

When KEXEC_SIG is not enabled, kernel should not load images through
kexec_file systemcall if the kernel is locked down unless IMA can be used
to validate the image.

[Modified by David Howells to fit with modifications to the previous patch
 and to return -EPERM if the kernel is locked down for consistency with
 other lockdowns]

Signed-off-by: Jiri Bohac <jbohac@...e.cz>
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Jiri Bohac <jbohac@...e.cz>
Cc: Matthew Garrett <mjg59@...f.ucam.org>
cc: Chun-Yi Lee <jlee@...e.com>
cc: kexec@...ts.infradead.org
---
 include/linux/ima.h | 6 ++++++
 kernel/kexec_file.c | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index b5e16b8c50b7..b35ed0725a05 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -127,4 +127,10 @@ static inline int ima_inode_removexattr(struct dentry *dentry,
 	return 0;
 }
 #endif /* CONFIG_IMA_APPRAISE */
+
+static inline bool is_ima_kexec_appraise_enabled(void)
+{
+	return IS_ENABLED(CONFIG_IMA_APPRAISE_REQUIRE_KEXEC_SIGS);
+}
+
 #endif /* _LINUX_IMA_H */
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 67f3a866eabe..b4e938dff4be 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -239,6 +239,14 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
 		}
 
 		ret = 0;
+		if (is_ima_kexec_appraise_enabled())
+			break;
+
+		if (kernel_is_locked_down(reason)) {
+			ret = -EPERM;
+			goto out;
+		}
+
 		break;
 
 		/* All other errors are fatal, including nomem, unparseable
-- 
2.21.0.352.gf09ad66450-goog