[PATCH V34 06/29] kexec_load: Disable at runtime if the kernel is locked down

Matthew Garrett
2019-06-22T00:04:21Z

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>
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 200175c8605a..00a31ab2e5ba 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -84,6 +84,7 @@ 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 68559808fdfa..ec3f07a4b1c0 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -207,6 +207,14 @@ 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 565c87451f0f..08fcd8116db3 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",
};
--
2.22.0.410.gd8fdbe21b5-goog