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Message-ID: <20180111120157.23qceywzi6omvvkb@dwarf.suse.cz>
Date: Thu, 11 Jan 2018 13:01:57 +0100
From: Jiri Bohac <jbohac@...e.cz>
To: David Howells <dhowells@...hat.com>
Cc: linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
jforbes@...hat.com, Chun-Yi Lee <joeyli.kernel@...il.com>
Subject: [PATCH 08a/30] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and
KEXEC_SIG_FORCE
This is a preparatory patch for kexec lockdown. A locked down kernel needs to
prevent unsigned kernel images to be loaded with kexec_file_load. Currently,
the only way to force the signature verification is compiling with
KEXEC_VERIFY_SIG. This prevents loading usigned images even when the kernel is
not locked down at runtime.
This patch spilts KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE.
Analogous to the MODULE_SIG and MODULE_SIG_FORCE for modules, KEXEC_SIG turns
on the signature verification but allows unsigned images to be loaded.
KEXEC_SIG_FORCE disallows images without a valid signature.
Signed-off-by: Jiri Bohac <jbohac@...e.cz>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8eed3f94bfc7..f25facb0df96 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1951,20 +1951,28 @@ config KEXEC_FILE
for kernel and initramfs as opposed to list of segments as
accepted by previous system call.
-config KEXEC_VERIFY_SIG
+config KEXEC_SIG
bool "Verify kernel signature during kexec_file_load() syscall"
depends on KEXEC_FILE
---help---
- This option makes kernel signature verification mandatory for
- the kexec_file_load() syscall.
+ This option makes the kexec_file_load() syscall check for a valid
+ signature of the kernel image. The image can still be loaded without
+ a valid signature unless you also enable KEXEC_SIG_FORCE.
- In addition to that option, you need to enable signature
+ In addition to this option, you need to enable signature
verification for the corresponding kernel image type being
loaded in order for this to work.
+config KEXEC_SIG_FORCE
+ bool "Require a valid signature in kexec_file_load() syscall"
+ depends on KEXEC_SIG
+ ---help---
+ This option makes kernel signature verification mandatory for
+ the kexec_file_load() syscall.
+
config KEXEC_BZIMAGE_VERIFY_SIG
bool "Enable bzImage signature verification support"
- depends on KEXEC_VERIFY_SIG
+ depends on KEXEC_SIG
depends on SIGNED_PE_FILE_VERIFICATION
select SYSTEM_TRUSTED_KEYRING
---help---
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 1f790cf9d38f..3fbe35b923ef 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -406,7 +406,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
return image->fops->cleanup(image->image_loader_data);
}
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
int arch_kexec_kernel_verify_sig(struct kimage *image, void *kernel,
unsigned long kernel_len)
{
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index f16f6ceb3875..19652372f3ee 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -121,7 +121,7 @@ typedef void *(kexec_load_t)(struct kimage *image, char *kernel_buf,
unsigned long cmdline_len);
typedef int (kexec_cleanup_t)(void *loader_data);
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
typedef int (kexec_verify_sig_t)(const char *kernel_buf,
unsigned long kernel_len);
#endif
@@ -130,7 +130,7 @@ struct kexec_file_ops {
kexec_probe_t *probe;
kexec_load_t *load;
kexec_cleanup_t *cleanup;
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
kexec_verify_sig_t *verify_sig;
#endif
};
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -45,7 +45,7 @@ int __weak arch_kimage_file_post_load_cleanup(struct kimage *image)
return -EINVAL;
}
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
int __weak arch_kexec_kernel_verify_sig(struct kimage *image, void *buf,
unsigned long buf_len)
{
@@ -116,7 +116,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
const char __user *cmdline_ptr,
unsigned long cmdline_len, unsigned flags)
{
- int ret = 0;
+ int ret = 0, sig_err = -EPERM;
void *ldata;
loff_t size;
@@ -135,15 +135,20 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
if (ret)
goto out;
-#ifdef CONFIG_KEXEC_VERIFY_SIG
- ret = arch_kexec_kernel_verify_sig(image, image->kernel_buf,
+#ifdef CONFIG_KEXEC_SIG
+ sig_err = arch_kexec_kernel_verify_sig(image, image->kernel_buf,
image->kernel_buf_len);
- if (ret) {
+ if (sig_err)
pr_debug("kernel signature verification failed.\n");
+ else
+ pr_debug("kernel signature verification successful.\n");
+#endif
+
+ if (sig_err && IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) {
+ ret = sig_err;
goto out;
}
- pr_debug("kernel signature verification successful.\n");
-#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, &image->initrd_buf,
--
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, Prague, Czechia
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