On 10/02/2019 05:49 PM, Mimi Zohar wrote:
On Tue, 2019-10-01 at 12:07 -0400, Nayna wrote:
On 09/30/2019 09:04 PM, Thiago Jung Bauermann wrote:
Hello,
Hi,
diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
new file mode 100644
index 000000000000..39401b67f19e
--- /dev/null
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Nayna Jain
+ */
+
+#include <linux/ima.h>
+#include <asm/secure_boot.h>
+
+bool arch_ima_get_secureboot(void)
+{
+ return is_powerpc_os_secureboot_enabled();
+}
+
+/* Defines IMA appraise rules for secureboot */
+static const char *const arch_rules[] = {
+ "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
+#if !IS_ENABLED(CONFIG_MODULE_SIG)
+ "appraise func=MODULE_CHECK appraise_type=imasig|modsig",
+#endif
+ NULL
+};
+
+/*
+ * Returns the relevant IMA arch policies based on the system secureboot state.
+ */
+const char *const *arch_get_ima_policy(void)
+{
+ if (is_powerpc_os_secureboot_enabled())
+ return arch_rules;
+
+ return NULL;
+}
If CONFIG_MODULE_SIG is enabled but module signatures aren't enforced,
then IMA won't enforce module signature either. x86's
arch_get_ima_policy() calls set_module_sig_enforced(). Doesn't the
powerpc version need to do that as well?
On the flip side, if module signatures are enforced by the module
subsystem then IMA will verify the signature a second time since there's
no sharing of signature verification results between the module
subsystem and IMA (this was observed by Mimi).
IMHO this is a minor issue, since module loading isn't a hot path and
the duplicate work shouldn't impact anything. But it could be avoided by
having a NULL entry in arch_rules, which arch_get_ima_policy() would
dynamically update with the "appraise func=MODULE_CHECK" rule if
is_module_sig_enforced() is true.
Thanks Thiago for reviewing. I am wondering that this will give two
meanings for NULL. Can we do something like below, there are possibly
two options ?
1. Set IMA_APPRAISED in the iint->flags if is_module_sig_enforced().
OR
2. Let ima_get_action() check for is_module_sig_enforced() when policy
is appraise and func is MODULE_CHECK.
I'm a bit hesitant about mixing the module subsystem signature
verification method with the IMA measure "template=ima-modsig" rules.
Does it actually work?
We can at least limit verifying the same appended signature twice to
when "module.sig_enforce" is specified on the boot command line, by
changing "!IS_ENABLED(CONFIG_MODULE_SIG)" to test
"CONFIG_MODULE_SIG_FORCE".
Yes this seems to be a better idea. I have implemented this in the v7
version of the ima_arch version.
Thanks & Regards,
- Nayna
