[PATCH 43/47][X] UBUNTU: SAUCE: (efi-lockdown) Lock down module params that specify hardware parameters (eg. ioport)

[Stefan Bader]

On 19.06.20 01:12, Seth Forshee wrote:
> From: David Howells <dhowells at redhat.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1884159
> 
> Provided an annotation for module parameters that specify hardware
> parameters (such as io ports, iomem addresses, irqs, dma channels, fixed
> dma buffers and other types).
> 
> Suggested-by: Alan Cox <gnomes at lxorguk.ukuu.org.uk>
> Signed-off-by: David Howells <dhowells at redhat.com>
> (backported from commit 33a38c67ed53106458e1858a2101cae3026486e4
>  git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
> Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
> ---

It is like upstream but I wonder whether tainting the kernel makes sense if
lockdown prevents changes...


>  kernel/params.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/params.c b/kernel/params.c
> index a6d6149c0fe6..87bbf2bdc09e 100644
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -108,13 +108,18 @@ bool parameq(const char *a, const char *b)
>  	return parameqn(a, b, strlen(a)+1);
>  }
>  
> -static void param_check_unsafe(const struct kernel_param *kp)
> +static bool param_check_unsafe(const struct kernel_param *kp,
> +			       const char *doing)
>  {
>  	if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
>  		pr_warn("Setting dangerous option %s - tainting kernel\n",
>  			kp->name);
>  		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
>  	}
> +
> +	if (kp->flags & KERNEL_PARAM_FL_HWPARAM && secure_modules())
> +		return false;
> +	return true;
>  }
>  
>  static int parse_one(char *param,
> @@ -144,8 +149,10 @@ static int parse_one(char *param,
>  			pr_debug("handling %s with %p\n", param,
>  				params[i].ops->set);
>  			kernel_param_lock(params[i].mod);
> -			param_check_unsafe(&params[i]);
> -			err = params[i].ops->set(val, &params[i]);
> +			if (param_check_unsafe(&params[i], doing))
> +				err = params[i].ops->set(val, &params[i]);
> +			else
> +				err = -EPERM;
>  			kernel_param_unlock(params[i].mod);
>  			return err;
>  		}
> @@ -608,6 +615,12 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
>  	return count;
>  }
>  
> +#ifdef CONFIG_MODULES
> +#define mod_name(mod) (mod)->name
> +#else
> +#define mod_name(mod) "unknown"
> +#endif
> +
>  /* sysfs always hands a nul-terminated string in buf.  We rely on that. */
>  static ssize_t param_attr_store(struct module_attribute *mattr,
>  				struct module_kobject *mk,
> @@ -620,8 +633,10 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
>  		return -EPERM;
>  
>  	kernel_param_lock(mk->mod);
> -	param_check_unsafe(attribute->param);
> -	err = attribute->param->ops->set(buf, attribute->param);
> +	if (param_check_unsafe(attribute->param, mod_name(mk->mod)))
> +		err = attribute->param->ops->set(buf, attribute->param);
> +	else
> +		err = -EPERM;
>  	kernel_param_unlock(mk->mod);
>  	if (!err)
>  		return len;
> 


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