2020-05-01 14:20:09

by Nayna Jain

Subject: [PATCH v2] powerpc/ima: fix secure boot rules in ima arch policy

To prevent verifying the kernel module appended signature twice
(finit_module), once by the module_sig_check() and again by IMA, powerpc
secure boot rules define an IMA architecture specific policy rule
only if CONFIG_MODULE_SIG_FORCE is not enabled. This, unfortunately, does
not take into account the ability of enabling "sig_enforce" on the boot
command line (module.sig_enforce=1).

Including the IMA module appraise rule results in failing the finit_module
syscall, unless the module signing public key is loaded onto the IMA
keyring.

This patch fixes secure boot policy rules to be based on CONFIG_MODULE_SIG
instead.

Fixes: 4238fad366a6 ("powerpc/ima: Add support to initialize ima policy rules")
Signed-off-by: Nayna Jain <[email protected]>
---
v2:
* Fixes the patch description to specify the problem more clearly as asked
by Michael Ellerman.

arch/powerpc/kernel/ima_arch.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
index e34116255ced..957abd592075 100644
--- a/arch/powerpc/kernel/ima_arch.c
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -19,12 +19,12 @@ bool arch_ima_get_secureboot(void)
* to be stored as an xattr or as an appended signature.
*
* To avoid duplicate signature verification as much as possible, the IMA
- * policy rule for module appraisal is added only if CONFIG_MODULE_SIG_FORCE
+ * policy rule for module appraisal is added only if CONFIG_MODULE_SIG
* is not enabled.
*/
static const char *const secure_rules[] = {
"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
-#ifndef CONFIG_MODULE_SIG_FORCE
+#ifndef CONFIG_MODULE_SIG
"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
#endif
NULL
@@ -50,7 +50,7 @@ static const char *const secure_and_trusted_rules[] = {
"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
"measure func=MODULE_CHECK template=ima-modsig",
"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
-#ifndef CONFIG_MODULE_SIG_FORCE
+#ifndef CONFIG_MODULE_SIG
"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
#endif
NULL
--
2.18.1

2020-05-07 03:21:38

by Mimi Zohar

Subject: Re: [PATCH v2] powerpc/ima: fix secure boot rules in ima arch policy

On Fri, 2020-05-01 at 10:16 -0400, Nayna Jain wrote:
> To prevent verifying the kernel module appended signature twice
> (finit_module), once by the module_sig_check() and again by IMA, powerpc
> secure boot rules define an IMA architecture specific policy rule
> only if CONFIG_MODULE_SIG_FORCE is not enabled. This, unfortunately, does
> not take into account the ability of enabling "sig_enforce" on the boot
> command line (module.sig_enforce=1).
>
> Including the IMA module appraise rule results in failing the finit_module
> syscall, unless the module signing public key is loaded onto the IMA
> keyring.
>
> This patch fixes secure boot policy rules to be based on CONFIG_MODULE_SIG
> instead.
>
> Fixes: 4238fad366a6 ("powerpc/ima: Add support to initialize ima policy rules")
> Signed-off-by: Nayna Jain <[email protected]>

Thanks, Nayna.

Signed-off-by: Mimi Zohar <[email protected]>

2020-05-13 12:45:42

by Michael Ellerman

Subject: Re: [PATCH v2] powerpc/ima: fix secure boot rules in ima arch policy

On Fri, 1 May 2020 10:16:52 -0400, Nayna Jain wrote:
> To prevent verifying the kernel module appended signature twice
> (finit_module), once by the module_sig_check() and again by IMA, powerpc
> secure boot rules define an IMA architecture specific policy rule
> only if CONFIG_MODULE_SIG_FORCE is not enabled. This, unfortunately, does
> not take into account the ability of enabling "sig_enforce" on the boot
> command line (module.sig_enforce=1).
>
> [...]

Applied to powerpc/fixes.

[1/1] powerpc/ima: Fix secure boot rules in ima arch policy
https://git.kernel.org/powerpc/c/fa4f3f56ccd28ac031ab275e673ed4098855fed4

cheers