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SubjectRe: [PATCH v2 2/4] powerpc: expose secure variables to userspace via sysfs
On Wed, Aug 21, 2019 at 11:08:21AM -0400, Nayna Jain wrote:
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-secvar
> @@ -0,0 +1,27 @@
> +What: /sys/firmware/secvar
> +Date: August 2019
> +Contact: Nayna Jain <nayna@linux.ibm.com>
> +Description:
> + This directory exposes interfaces for interacting with
> + the secure variables managed by OPAL firmware.
> +
> + This is only for the powerpc/powernv platform.
> +
> + Directory:
> + vars: This directory lists all the variables that
> + are supported by the OPAL. The variables are
> + represented in the form of directories with
> + their variable names. The variable name is
> + unique and is in ASCII representation. The data
> + and size can be determined by reading their
> + respective attribute files.
> +
> + Each variable directory has the following files:
> + name: An ASCII representation of the variable name
> + data: A read-only file containing the value of the
> + variable
> + size: An integer representation of the size of the
> + content of the variable. In other works, it
> + represents the size of the data
> + update: A write-only file that is used to submit the new
> + value for the variable.

Can you break this out into one-entry-per-file like most other entries
are defined? That makes it easier for tools to parse (specifically the
tool in the tree right now...)



> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 42109682b727..b4bdf77837b2 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -925,6 +925,15 @@ config PPC_SECURE_BOOT
> allows user to enable OS Secure Boot on PowerPC systems that
> have firmware secure boot support.
>
> +config SECVAR_SYSFS
> + tristate "Enable sysfs interface for POWER secure variables"
> + depends on PPC_SECURE_BOOT

No depends on SYSFS?

> + help
> + POWER secure variables are managed and controlled by firmware.
> + These variables are exposed to userspace via sysfs to enable
> + read/write operations on these variables. Say Y if you have
> + secure boot enabled and want to expose variables to userspace.

Mix of tabs and spaces :(

> +
> endmenu
>
> config ISA_DMA_API
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 9041563f1c74..4ea7b738c3a3 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -158,6 +158,7 @@ obj-$(CONFIG_EPAPR_PARAVIRT) += epapr_paravirt.o epapr_hcalls.o
> obj-$(CONFIG_KVM_GUEST) += kvm.o kvm_emul.o
>
> obj-$(CONFIG_PPC_SECURE_BOOT) += secboot.o ima_arch.o secvar-ops.o
> +obj-$(CONFIG_SECVAR_SYSFS) += secvar-sysfs.o

No tab?

>
> # Disable GCOV, KCOV & sanitizers in odd or sensitive code
> GCOV_PROFILE_prom_init.o := n
> diff --git a/arch/powerpc/kernel/secvar-sysfs.c b/arch/powerpc/kernel/secvar-sysfs.c
> new file mode 100644
> index 000000000000..e46986bb29a0
> --- /dev/null
> +++ b/arch/powerpc/kernel/secvar-sysfs.c
> @@ -0,0 +1,210 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 IBM Corporation <nayna@linux.ibm.com>
> + *
> + * This code exposes secure variables to user via sysfs
> + */
> +
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/compat.h>
> +#include <linux/string.h>
> +#include <asm/opal.h>
> +#include <asm/secvar.h>
> +
> +//Approximating it for now, it is bound to change.

" " before "A" here please.

> +#define VARIABLE_MAX_SIZE 32000
> +
> +static struct kobject *powerpc_kobj;
> +static struct secvar_operations *secvarops;
> +struct kset *secvar_kset;
> +
> +static ssize_t name_show(struct kobject *kobj, struct kobj_attribute *attr,
> + char *buf)
> +{
> + return sprintf(buf, "%s", kobj->name);
> +}

Why do you need this entry as it is the directory name? Userspace
already "knows" it if they can open this file.


> +
> +static ssize_t size_show(struct kobject *kobj, struct kobj_attribute *attr,
> + char *buf)
> +{
> + unsigned long dsize;
> + int rc;
> +
> + rc = secvarops->get_variable(kobj->name, strlen(kobj->name) + 1, NULL,
> + &dsize);
> + if (rc) {
> + pr_err("Error retrieving variable size %d\n", rc);
> + return rc;
> + }
> +
> + rc = sprintf(buf, "%ld", dsize);
> +
> + return rc;
> +}
> +
> +static ssize_t data_read(struct file *filep, struct kobject *kobj,
> + struct bin_attribute *attr, char *buf, loff_t off,
> + size_t count)
> +{
> + unsigned long dsize;
> + int rc;
> + char *data;
> +
> + rc = secvarops->get_variable(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 %ld\n", dsize);
> +
> + data = kzalloc(dsize, GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + rc = secvarops->get_variable(kobj->name, strlen(kobj->name)+1, data,
> + &dsize);
> + if (rc) {
> + pr_err("Error getting variable %d\n", rc);
> + goto data_fail;
> + }
> +
> + rc = memory_read_from_buffer(buf, count, &off, data, dsize);
> +
> +data_fail:
> + kfree(data);
> + return rc;
> +}
> +
> +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 = secvarops->set_variable(kobj->name, strlen(kobj->name)+1, buf,
> + count);
> + if (rc) {
> + pr_err("Error setting the variable %s\n", kobj->name);
> + return rc;
> + }
> +
> + return count;
> +}
> +
> +static struct kobj_attribute name_attr =
> +__ATTR(name, 0444, name_show, NULL);

__ATTR_RO()?

> +
> +static struct kobj_attribute size_attr =
> +__ATTR(size, 0444, size_show, NULL);

__ATTR_RO()?

> +
> +static struct bin_attribute data_attr = {
> + .attr = {.name = "data", .mode = 0444},
> + .size = VARIABLE_MAX_SIZE,
> + .read = data_read,
> +};

__BIN_ATTR_RO()?

> +
> +
> +static struct bin_attribute update_attr = {
> + .attr = {.name = "update", .mode = 0200},
> + .size = VARIABLE_MAX_SIZE,
> + .write = update_write,
> +};

__BIN_ATTR_RO()?


> +
> +static struct bin_attribute *secvar_bin_attrs[] = {
> + &data_attr,
> + &update_attr,
> + NULL,
> +};
> +
> +static struct attribute *secvar_attrs[] = {
> + &name_attr.attr,
> + &size_attr.attr,
> + NULL,
> +};
> +
> +const struct attribute_group secvar_attr_group = {
> + .attrs = secvar_attrs,
> + .bin_attrs = secvar_bin_attrs,
> +};

static?

> +
> +int secvar_sysfs_load(void)
> +{
> +
> + char *name;

No blank line. You didn't run this this through checkpatch, did you :(


> + unsigned long namesize;
> + struct kobject *kobj;
> + int status;
> + int rc = 0;
> +
> + name = kzalloc(1024, GFP_KERNEL);

Why 1024?

> + if (!name)
> + return -ENOMEM;
> +
> + do {
> +
> + status = secvarops->get_next_variable(name, &namesize, 1024);
> + if (status != OPAL_SUCCESS)
> + break;
> +
> + pr_info("name is %s\n", name);

Please delete debugging messages.

> + kobj = kobject_create_and_add(name, &(secvar_kset->kobj));
> + if (kobj) {
> + rc = sysfs_create_group(kobj, &secvar_attr_group);

You just raced userspace and lost :(

If you set your kobj_type to have the attribute group you will not race
and loose, the core will handle it for you.


> + if (rc)
> + pr_err("Error creating attributes for %s variable\n",
> + name);
> + } else {
> + pr_err("Error creating sysfs entry for %s variable\n",
> + name);
> + rc = -EINVAL;
> + }
> +
> + } while ((status == OPAL_SUCCESS) && (rc == 0));
> +
> + kfree(name);
> + return rc;
> +}
> +
> +int secvar_sysfs_init(void)
> +{
> + powerpc_kobj = kobject_create_and_add("secvar", firmware_kobj);
> + if (!powerpc_kobj) {
> + pr_err("secvar: Failed to create firmware kobj\n");
> + return -ENODEV;
> + }
> +
> + secvar_kset = kset_create_and_add("vars", NULL, powerpc_kobj);
> + if (!secvar_kset) {
> + pr_err("secvar: sysfs kobject registration failed.\n");

You juat leaked a kobject :(

> + return -ENODEV;
> + }
> +
> + secvarops = get_secvar_ops();
> + if (!secvarops) {
> + kobject_put(powerpc_kobj);
> + pr_err("secvar: failed to retrieve secvar operations.\n");
> + return -ENODEV;

You just leaked 2 things from above :(

> + }
> +
> + secvar_sysfs_load();
> + pr_info("Secure variables sysfs initialized");

Do not be noisy when all goes just fine. The kernel log should be quiet
when all goes well.

thanks,

greg k-h

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