Re: [PATCH v4 1/6] x86/ima: define arch_ima_get_secureboot

Re: [PATCH v4 1/6] x86/ima: define arch_ima_get_secureboot

[Mimi Zohar]

[Cc'ing the kexec mailing list, and Seth]

On Wed, 2018-09-26 at 17:52 +0530, Nayna Jain wrote:
> Distros are concerned about totally disabling the kexec_load syscall.
> As a compromise, the kexec_load syscall will only be disabled when
> CONFIG_KEXEC_VERIFY_SIG is configured and the system is booted with
> secureboot enabled.
> 
> This patch defines the new arch specific function called
> arch_ima_get_secureboot() to retrieve the secureboot state of the system.
> 
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
> Suggested-by: Seth Forshee <seth.forshee@canonical.com>

Nice!

Mimi

> ---
>  arch/x86/kernel/Makefile   |  2 ++
>  arch/x86/kernel/ima_arch.c | 17 +++++++++++++++++
>  include/linux/ima.h        |  9 +++++++++
>  3 files changed, 28 insertions(+)
>  create mode 100644 arch/x86/kernel/ima_arch.c
> 
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 02d6f5cf4e70..f32406e51424 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -149,3 +149,5 @@ ifeq ($(CONFIG_X86_64),y)
>  	obj-$(CONFIG_MMCONF_FAM10H)	+= mmconf-fam10h_64.o
>  	obj-y				+= vsmp_64.o
>  endif
> +
> +obj-$(CONFIG_IMA)			+= ima_arch.o
> diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
> new file mode 100644
> index 000000000000..bb5a88d2b271
> --- /dev/null
> +++ b/arch/x86/kernel/ima_arch.c
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Copyright (C) 2018 IBM Corporation
> + */
> +#include <linux/efi.h>
> +#include <linux/ima.h>
> +
> +extern struct boot_params boot_params;
> +
> +bool arch_ima_get_secureboot(void)
> +{
> +	if (efi_enabled(EFI_BOOT) &&
> +		(boot_params.secure_boot == efi_secureboot_mode_enabled))
> +		return true;
> +	else
> +		return false;
> +}
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 84806b54b50a..4852255aa4f4 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -30,6 +30,15 @@ extern void ima_post_path_mknod(struct dentry *dentry);
>  extern void ima_add_kexec_buffer(struct kimage *image);
>  #endif
>  
> +#ifdef CONFIG_X86
> +extern bool arch_ima_get_secureboot(void);
> +#else
> +static inline bool arch_ima_get_secureboot(void)
> +{
> +	return false;
> +}
> +#endif
> +
>  #else
>  static inline int ima_bprm_check(struct linux_binprm *bprm)
>  {


_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

Re: [PATCH v4 2/6] ima: prevent kexec_load syscall based on runtime secureboot flag

[Mimi Zohar]

[Cc'ing the kexec mailing list, and Seth]

On Wed, 2018-09-26 at 17:52 +0530, Nayna Jain wrote:
> When CONFIG_KEXEC_VERIFY_SIG is enabled, the kexec_file_load syscall
> requires the kexec'd kernel image to be signed. Distros are concerned
> about totally disabling the kexec_load syscall. As a compromise, the
> kexec_load syscall will only be disabled when CONFIG_KEXEC_VERIFY_SIG
> is configured and the system is booted with secureboot enabled.
> 
> This patch disables the kexec_load syscall only for systems booted with
> secureboot enabled.
> 
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>

Nice!

Mimi

> ---
>  security/integrity/ima/ima_main.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index dce0a8a217bb..bdb6e5563d05 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -505,20 +505,24 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>   */
>  int ima_load_data(enum kernel_load_data_id id)
>  {
> -	bool sig_enforce;
> +	bool ima_enforce, sig_enforce;
>  
> -	if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
> -		return 0;
> +	ima_enforce =
> +		(ima_appraise & IMA_APPRAISE_ENFORCE) == IMA_APPRAISE_ENFORCE;
>  
>  	switch (id) {
>  	case LOADING_KEXEC_IMAGE:
> -		if (ima_appraise & IMA_APPRAISE_KEXEC) {
> +#ifdef CONFIG_KEXEC_VERIFY_SIG
> +		if (arch_ima_get_secureboot())
> +			return -EACCES;
> +#endif
> +		if (ima_enforce && (ima_appraise & IMA_APPRAISE_KEXEC)) {
>  			pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}
>  		break;
>  	case LOADING_FIRMWARE:
> -		if (ima_appraise & IMA_APPRAISE_FIRMWARE) {
> +		if (ima_enforce && (ima_appraise & IMA_APPRAISE_FIRMWARE)) {
>  			pr_err("Prevent firmware sysfs fallback loading.\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}
> @@ -526,7 +530,8 @@ int ima_load_data(enum kernel_load_data_id id)
>  	case LOADING_MODULE:
>  		sig_enforce = is_module_sig_enforced();
>  
> -		if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES)) {
> +		if (ima_enforce && (!sig_enforce
> +				    && (ima_appraise & IMA_APPRAISE_MODULES))) {
>  			pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}


_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec