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Message-ID: <840dae63-5a90-1327-437e-1ed92e165754@gmail.com>
Date: Mon, 2 Jul 2018 11:31:09 -0700
From: J Freyensee <why2jjj.linux@...il.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>,
linux-integrity@...r.kernel.org
Cc: linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
"Luis R . Rodriguez" <mcgrof@...nel.org>,
Eric Biederman <ebiederm@...ssion.com>,
kexec@...ts.infradead.org, Andres Rodriguez <andresx7@...il.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v5 3/8] ima: based on policy require signed kexec kernel
images
On 7/2/18 7:37 AM, Mimi Zohar wrote:
> The original kexec_load syscall can not verify file signatures, nor can
> the kexec image be measured. Based on policy, deny the kexec_load
> syscall.
Curiosity question: I thought kexec_load() syscall was used to load a
crashdump? If this is true, how would this work if kexec_load() is
being denied? I don't think I'd want to be hindered in cases where I'm
trying to diagnose a crash.
Thanks,
Jay
> Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Luis R. Rodriguez <mcgrof@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: David Howells <dhowells@...hat.com>
>
> ---
> Changelog v3:
> - use switch/case
>
> include/linux/ima.h | 7 +++++++
> security/integrity/ima/ima.h | 1 +
> security/integrity/ima/ima_main.c | 27 +++++++++++++++++++++++++++
> security/integrity/ima/ima_policy.c | 2 ++
> security/security.c | 7 ++++++-
> 5 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 0e4647e0eb60..84806b54b50a 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -11,6 +11,7 @@
> #define _LINUX_IMA_H
>
> #include <linux/fs.h>
> +#include <linux/security.h>
> #include <linux/kexec.h>
> struct linux_binprm;
>
> @@ -19,6 +20,7 @@ extern int ima_bprm_check(struct linux_binprm *bprm);
> extern int ima_file_check(struct file *file, int mask, int opened);
> extern void ima_file_free(struct file *file);
> extern int ima_file_mmap(struct file *file, unsigned long prot);
> +extern int ima_load_data(enum kernel_load_data_id id);
> extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
> extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
> enum kernel_read_file_id id);
> @@ -49,6 +51,11 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
> return 0;
> }
>
> +static inline int ima_load_data(enum kernel_load_data_id id)
> +{
> + return 0;
> +}
> +
> static inline int ima_read_file(struct file *file, enum kernel_read_file_id id)
> {
> return 0;
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 2ab1affffa36..588e4813370c 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -232,6 +232,7 @@ int ima_policy_show(struct seq_file *m, void *v);
> #define IMA_APPRAISE_MODULES 0x08
> #define IMA_APPRAISE_FIRMWARE 0x10
> #define IMA_APPRAISE_POLICY 0x20
> +#define IMA_APPRAISE_KEXEC 0x40
>
> #ifdef CONFIG_IMA_APPRAISE
> int ima_appraise_measurement(enum ima_hooks func,
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index dca44cf7838e..71fecfef0939 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -496,6 +496,33 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
> MAY_READ, func, 0);
> }
>
> +/**
> + * ima_load_data - appraise decision based on policy
> + * @id: kernel load data caller identifier
> + *
> + * Callers of this LSM hook can not measure, appraise, or audit the
> + * data provided by userspace. Enforce policy rules requring a file
> + * signature (eg. kexec'ed kernel image).
> + *
> + * For permission return 0, otherwise return -EACCES.
> + */
> +int ima_load_data(enum kernel_load_data_id id)
> +{
> + if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
> + return 0;
> +
> + switch (id) {
> + case LOADING_KEXEC_IMAGE:
> + if (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 */
> + }
> + default:
> + break;
> + }
> + return 0;
> +}
> +
> static int __init init_ima(void)
> {
> int error;
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 7f4a4de7e831..ebfb389b79df 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -448,6 +448,8 @@ static int ima_appraise_flag(enum ima_hooks func)
> return IMA_APPRAISE_FIRMWARE;
> else if (func == POLICY_CHECK)
> return IMA_APPRAISE_POLICY;
> + else if (func == KEXEC_KERNEL_CHECK)
> + return IMA_APPRAISE_KEXEC;
> return 0;
> }
>
> diff --git a/security/security.c b/security/security.c
> index 05fe5b1932d7..7b870df0a335 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1063,7 +1063,12 @@ EXPORT_SYMBOL_GPL(security_kernel_post_read_file);
>
> int security_kernel_load_data(enum kernel_load_data_id id)
> {
> - return call_int_hook(kernel_load_data, 0, id);
> + int ret;
> +
> + ret = call_int_hook(kernel_load_data, 0, id);
> + if (ret)
> + return ret;
> + return ima_load_data(id);
> }
>
> int security_task_fix_setuid(struct cred *new, const struct cred *old,
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