A kernel builder may not enable KEXEC_SIG and some architectures like
ppc64 simply don't have KEXEC_SIG. In these cases, unless both
IMA_ARCH_POLICY and secure boot also enabled, lockdown doesn't prevent
unsigned kernel image from being kexec'ed via the kexec_file_load
syscall whereas it could prevent one via the kexec_load syscall. Mandate
signature verification for those cases.
Fixes: 155bdd30af17 ("kexec_file: Restrict at runtime if the kernel is locked down")
Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
Cc: Jiri Bohac <jbohac@xxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: linux-integrity@xxxxxxxxxxxxxxx
Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
v3
- add lockdown tests to explain why kexec_file_load failed [Mimi]
v2
- collect reviewed-by tag from Mimi
- s/mandate_signatute_verification/mandate_signature_verification [Mimi]
- return the status of kexec_image_verify_sig correctly when signature
verification is not mandated
---
kernel/kexec_file.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index dd5983010b7b..2c1054ab21ef 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -125,6 +125,17 @@ void kimage_file_post_load_cleanup(struct kimage *image)
image->image_loader_data = NULL;
}
+static bool mandate_signature_verification(void)
+{
+ /*
+ * If IMA is guaranteed to appraise a signature on the kexec
+ * image, permit it even if the kernel is otherwise locked
+ * down.
+ */
+ return !ima_appraise_signature(READING_KEXEC_IMAGE) &&
+ security_locked_down(LOCKDOWN_KEXEC);
+}
+
#ifdef CONFIG_KEXEC_SIG
#ifdef CONFIG_SIGNED_PE_FILE_VERIFICATION
int kexec_kernel_verify_pe_sig(const char *kernel, unsigned long kernel_len)
@@ -168,13 +179,7 @@ kimage_validate_signature(struct kimage *image)
return ret;
}
- /*
- * If IMA is guaranteed to appraise a signature on the kexec
- * image, permit it even if the kernel is otherwise locked
- * down.
- */
- if (!ima_appraise_signature(READING_KEXEC_IMAGE) &&
- security_locked_down(LOCKDOWN_KEXEC))
+ if (mandate_signature_verification())
return -EPERM;
pr_debug("kernel signature verification failed (%d).\n", ret);
@@ -211,10 +216,13 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
#ifdef CONFIG_KEXEC_SIG
ret = kimage_validate_signature(image);
-
+#else
+ if (mandate_signature_verification())
+ ret = -EPERM;
+#endif
if (ret)
goto out;
-#endif
+
/* It is possible that there no initramfs is being loaded */
if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
ret = kernel_read_file_from_fd(initrd_fd, 0, &image->initrd_buf,
--
2.38.1
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