linux-kernel - Re: [PATCH v5 2/4] powerpc: expose secure variables to userspace via sysfs

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Message-ID: <33275df6-9ee8-989f-9857-20946fb64b25@linux.microsoft.com>
Date:   Fri, 25 Oct 2019 08:58:35 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Nayna Jain <nayna@...ux.ibm.com>, linuxppc-dev@...abs.org,
        linux-efi@...r.kernel.org, linux-integrity@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jeremy Kerr <jk@...abs.org>,
        Matthew Garret <matthew.garret@...ula.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        George Wilson <gcwilson@...ux.ibm.com>,
        Elaine Palmer <erpalmer@...ibm.com>,
        Eric Ricther <erichte@...ux.ibm.com>,
        Oliver O'Halloran <oohall@...il.com>
Subject: Re: [PATCH v5 2/4] powerpc: expose secure variables to userspace via
 sysfs

On 10/24/19 5:47 PM, Nayna Jain wrote:

> +static ssize_t size_show(struct kobject *kobj, struct kobj_attribute *attr,
> +			 char *buf)
> +{
> +	uint64_t dsize;
> +	int rc;
> +
> +	rc = secvar_ops->get(kobj->name, strlen(kobj->name) + 1, NULL, &dsize);
> +	if (rc) {
> +		pr_err("Error retrieving variable size %d\n", rc);
> +		return rc;
> +	}
> +
> +	rc = sprintf(buf, "%llu\n", dsize);
> +
> +	return rc;
> +}
nit: change it to "return sprintf(buf, "%llu\n", dsize);" instead.

> +
> +static ssize_t data_read(struct file *filep, struct kobject *kobj,
> +			 struct bin_attribute *attr, char *buf, loff_t off,
> +			 size_t count)
> +{
> +	uint64_t dsize;
> +	char *data;
> +	int rc;
> +
> +	rc = secvar_ops->get(kobj->name, strlen(kobj->name) + 1, NULL, &dsize);
> +	if (rc) {
> +		pr_err("Error getting variable size %d\n", rc);
> +		return rc;
> +	}
> +	pr_debug("dsize is %llu\n", dsize);
> +
> +	data = kzalloc(dsize, GFP_KERNEL);
Is there any MAX\MIN limit on dsize that can be returned by secvar_ops?
Is it ok to not validate the dsize
> +
> +static ssize_t update_write(struct file *filep, struct kobject *kobj,
> +			    struct bin_attribute *attr, char *buf, loff_t off,
> +			    size_t count)
> +{
> +	int rc;
> +
> +	pr_debug("count is %ld\n", count);
> +	rc = secvar_ops->set(kobj->name, strlen(kobj->name)+1, buf, count);
> +	if (rc) {
> +		pr_err("Error setting the variable %s\n", kobj->name);
> +		return rc;
> +	}
> +
> +	return count;
> +}
Return value from this function can be a count (of bytes in buf?) or 
error code. Could cause confusion.
> +
> +static int secvar_sysfs_load(void)
> +{
> +	char *name;
> +	uint64_t namesize = 0;
> +	struct kobject *kobj;
> +	int rc;
> +
> +	name = kzalloc(NAME_MAX_SIZE, GFP_KERNEL);
> +	if (!name)
> +		return -ENOMEM;
> +
> +	do {
> +		rc = secvar_ops->get_next(name, &namesize, NAME_MAX_SIZE);
> +		if (rc) {
> +			if (rc != -ENOENT)
> +				pr_err("error getting secvar from firmware %d\n",
> +					rc);
> +			break;
> +		}
> +
> +		kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);
> +		if (!kobj)
> +			return -ENOMEM;

Memory allocated for "name" is leaked in this case.

> +
> +		kobject_init(kobj, &secvar_ktype);
> +
> +		rc = kobject_add(kobj, &secvar_kset->kobj, "%s", name);
> +		if (rc) {
> +			pr_warn("kobject_add error %d for attribute: %s\n", rc,
> +				name);
> +			kobject_put(kobj);
> +			kobj = NULL;
> +		}
> +
> +		if (kobj)
> +			kobject_uevent(kobj, KOBJ_ADD);
> +
> +	} while (!rc);
> +
> +	kfree(name);
> +	return rc;
> +}