diff mbox series

[v2,1/3] firmware: Add boot information to sysfs

Message ID 20220203115344.267159-2-joel@jms.id.au (mailing list archive)
State New, archived
Headers show
Series firmware: Add boot information to sysfs | expand

Commit Message

Joel Stanley Feb. 3, 2022, 11:53 a.m. UTC 
Machines often have firmware that perform some action before Linux is
loaded. It's useful to know how this firmware is configured, so create a
sysfs directory and some properties that a system can choose to expose
to describe how the system was started.

Currently the intended use describes five files, relating to hardware
root of trust configuration.

These properties are populated by platform code at startup. Using fixed
values is suitable as the state that the system booted in will not
change after firmware has handed over.

Signed-off-by: Joel Stanley <joel@jms.id.au>
---
v2:
 - Rewrite so properties are present in common code and are exposed based
   on the is_visible callback.
 - Use sysfs_emit
---
 .../ABI/testing/sysfs-firmware-bootinfo       | 43 +++++++++
 drivers/base/firmware.c                       | 90 +++++++++++++++++++
 include/linux/firmware_bootinfo.h             | 22 +++++
 3 files changed, 155 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-bootinfo
 create mode 100644 include/linux/firmware_bootinfo.h

Comments

Greg Kroah-Hartman Feb. 3, 2022, 12:44 p.m. UTC | #1 
On Thu, Feb 03, 2022 at 10:23:42PM +1030, Joel Stanley wrote:
> Machines often have firmware that perform some action before Linux is
> loaded. It's useful to know how this firmware is configured, so create a
> sysfs directory and some properties that a system can choose to expose
> to describe how the system was started.
> 
> Currently the intended use describes five files, relating to hardware
> root of trust configuration.
> 
> These properties are populated by platform code at startup. Using fixed
> values is suitable as the state that the system booted in will not
> change after firmware has handed over.
> 
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> ---
> v2:
>  - Rewrite so properties are present in common code and are exposed based
>    on the is_visible callback.
>  - Use sysfs_emit
> ---
>  .../ABI/testing/sysfs-firmware-bootinfo       | 43 +++++++++
>  drivers/base/firmware.c                       | 90 +++++++++++++++++++
>  include/linux/firmware_bootinfo.h             | 22 +++++
>  3 files changed, 155 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-firmware-bootinfo
>  create mode 100644 include/linux/firmware_bootinfo.h
> 
> diff --git a/Documentation/ABI/testing/sysfs-firmware-bootinfo b/Documentation/ABI/testing/sysfs-firmware-bootinfo
> new file mode 100644
> index 000000000000..cd6c42316345
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-bootinfo
> @@ -0,0 +1,43 @@
> +What:		/sys/firmware/bootinfo/*
> +Date:		Jan 2022
> +Description:
> +		A system can expose information about how it was started in
> +		this directory.
> +
> +		This information is agnostic as to the firmware implementation.
> +
> +		A system may expose a subset of these properties as applicable.
> +
> +
> +What:		/sys/firmware/bootinfo/secure_boot
> +Date:		Jan 2022
> +Description:
> +		Indicates the system was started with secure boot enabled in
> +		the firmware.
> +
> +
> +What:		/sys/firmware/bootinfo/abr_image
> +Date:		Jan 2022
> +Description:
> +		Indicates the system was started from the alternate image
> +		loaded from an Alternate Boot Region. Often this is a result of
> +		the primary firmware image failing to start the system.
> +
> +
> +What:		/sys/firmware/bootinfo/low_security_key
> +Date:		Jan 2022
> +Description:
> +		Indicates the system's secure boot was verified with a low
> +		security or development key.
> +
> +What:		/sys/firmware/bootinfo/otp_protected
> +Date:		Jan 2022
> +Description:
> +		Indicates the system's boot configuration region is write
> +		protected and cannot be modified.
> +
> +What:		/sys/firmware/bootinfo/uart_boot
> +Date:		Jan 2022
> +Description:
> +		Indicates the system firmware was loaded from a UART instead of
> +		an internal boot device.
> diff --git a/drivers/base/firmware.c b/drivers/base/firmware.c
> index 8dff940e0db9..24b931232eb2 100644
> --- a/drivers/base/firmware.c
> +++ b/drivers/base/firmware.c
> @@ -11,6 +11,7 @@
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/device.h>
> +#include <linux/firmware_bootinfo.h>
>  
>  #include "base.h"
>  
> @@ -24,3 +25,92 @@ int __init firmware_init(void)
>  		return -ENOMEM;
>  	return 0;
>  }
> +
> +/*
> + * Exposes attributes documented in Documentation/ABI/testing/sysfs-firmware-bootinfo
> + */
> +static struct bootinfo bootinfo;
> +
> +static ssize_t abr_image_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.abr_image.val);
> +}
> +static DEVICE_ATTR_RO(abr_image);
> +
> +static ssize_t low_security_key_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.low_security_key.val);
> +}
> +static DEVICE_ATTR_RO(low_security_key);
> +
> +static ssize_t otp_protected_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.otp_protected.val);
> +}
> +static DEVICE_ATTR_RO(otp_protected);
> +
> +static ssize_t secure_boot_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.secure_boot.val);
> +}
> +static DEVICE_ATTR_RO(secure_boot);
> +
> +static ssize_t uart_boot_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.uart_boot.val);
> +}
> +static DEVICE_ATTR_RO(uart_boot);
> +
> +#define ATTR_ENABLED(a) ((attr == &dev_attr_##a.attr) && bootinfo.a.en)
> +
> +static umode_t bootinfo_attr_mode(struct kobject *kobj, struct attribute *attr, int index)
> +{
> +	if (ATTR_ENABLED(abr_image))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(otp_protected))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(low_security_key))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(otp_protected))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(low_security_key))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(secure_boot))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(uart_boot))
> +		return 0444;
> +
> +	return 0;
> +}
> +
> +static struct attribute *bootinfo_attrs[] = {
> +	&dev_attr_abr_image.attr,
> +	&dev_attr_low_security_key.attr,
> +	&dev_attr_otp_protected.attr,
> +	&dev_attr_secure_boot.attr,
> +	&dev_attr_uart_boot.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group bootinfo_attr_group = {
> +	.attrs = bootinfo_attrs,
> +	.is_visible = bootinfo_attr_mode,
> +};
> +
> +int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init)
> +{
> +	struct kobject *kobj = kobject_create_and_add("bootinfo", firmware_kobj);
> +	if (!kobj)
> +		return -ENOMEM;
> +
> +	memcpy(&bootinfo, bootinfo_init, sizeof(bootinfo));
> +
> +	return sysfs_create_group(kobj, &bootinfo_attr_group);
> +}
> +EXPORT_SYMBOL_GPL(firmware_bootinfo_init);
> diff --git a/include/linux/firmware_bootinfo.h b/include/linux/firmware_bootinfo.h
> new file mode 100644
> index 000000000000..3fe630b061b9
> --- /dev/null
> +++ b/include/linux/firmware_bootinfo.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */

I have to ask, do you really mean "or later"?


> +/* Copyright 2022 IBM Corp. */
> +
> +#include <linux/sysfs.h>
> +#include <linux/init.h>
> +
> +#define BOOTINFO_SET(b, n, v) b.n.en = true; b.n.val = v

Please use a while {} loop around these two statements.

Didn't checkpatch warn you about that?

> +struct bootinfo_entry {
> +	bool en;

What does "en" mean?  "enabled"?  If so, please spell it out.

> +	bool val;

How can a "value" have a boolean?  Is this "valid"?  Again, please spell
it out, we have no lack of letters to use here to keep people from being
confused.

Can you please use kernel-doc comments to describe this structure?


> +};
> +
> +struct bootinfo {
> +	struct bootinfo_entry abr_image;
> +	struct bootinfo_entry low_security_key;
> +	struct bootinfo_entry otp_protected;
> +	struct bootinfo_entry secure_boot;
> +	struct bootinfo_entry uart_boot;
> +};

Same here, please use kernel-doc

> +
> +int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init);

__init is not needed on a function definition like this.

thanks,

greg k-h
Robin Murphy Feb. 3, 2022, 2:22 p.m. UTC | #2 
On 2022-02-03 11:53, Joel Stanley wrote:
> Machines often have firmware that perform some action before Linux is
> loaded. It's useful to know how this firmware is configured, so create a
> sysfs directory and some properties that a system can choose to expose
> to describe how the system was started.
> 
> Currently the intended use describes five files, relating to hardware
> root of trust configuration.
> 
> These properties are populated by platform code at startup. Using fixed
> values is suitable as the state that the system booted in will not
> change after firmware has handed over.
> 
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> ---
> v2:
>   - Rewrite so properties are present in common code and are exposed based
>     on the is_visible callback.
>   - Use sysfs_emit
> ---
>   .../ABI/testing/sysfs-firmware-bootinfo       | 43 +++++++++
>   drivers/base/firmware.c                       | 90 +++++++++++++++++++
>   include/linux/firmware_bootinfo.h             | 22 +++++
>   3 files changed, 155 insertions(+)
>   create mode 100644 Documentation/ABI/testing/sysfs-firmware-bootinfo
>   create mode 100644 include/linux/firmware_bootinfo.h
> 
> diff --git a/Documentation/ABI/testing/sysfs-firmware-bootinfo b/Documentation/ABI/testing/sysfs-firmware-bootinfo
> new file mode 100644
> index 000000000000..cd6c42316345
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-bootinfo
> @@ -0,0 +1,43 @@
> +What:		/sys/firmware/bootinfo/*
> +Date:		Jan 2022
> +Description:
> +		A system can expose information about how it was started in
> +		this directory.
> +
> +		This information is agnostic as to the firmware implementation.
> +
> +		A system may expose a subset of these properties as applicable.
> +
> +
> +What:		/sys/firmware/bootinfo/secure_boot
> +Date:		Jan 2022
> +Description:
> +		Indicates the system was started with secure boot enabled in
> +		the firmware.
> +
> +
> +What:		/sys/firmware/bootinfo/abr_image
> +Date:		Jan 2022
> +Description:
> +		Indicates the system was started from the alternate image
> +		loaded from an Alternate Boot Region. Often this is a result of
> +		the primary firmware image failing to start the system.
> +
> +
> +What:		/sys/firmware/bootinfo/low_security_key
> +Date:		Jan 2022
> +Description:
> +		Indicates the system's secure boot was verified with a low
> +		security or development key.
> +
> +What:		/sys/firmware/bootinfo/otp_protected
> +Date:		Jan 2022
> +Description:
> +		Indicates the system's boot configuration region is write
> +		protected and cannot be modified.
> +
> +What:		/sys/firmware/bootinfo/uart_boot
> +Date:		Jan 2022
> +Description:
> +		Indicates the system firmware was loaded from a UART instead of
> +		an internal boot device.

I'd be concerned about how well details like "uart_boot" and "abr_image" 
scale beyond one SoC family from one vendor. The combinatorial explosion 
of possible boot configurations across Linux-capable SoCs and firmware 
in general is larger than I'd care to imagine, even before considering 
that the nuances don't necessarily stop there - e.g. whether a given 
storage interface is hard-wired or user-accessible is not a fixed 
property on many SoCs, and even a socketed SD card might be "trusted" if 
a board is deployed in a product with a sealed enclosure.

Cheers,
Robin.

> diff --git a/drivers/base/firmware.c b/drivers/base/firmware.c
> index 8dff940e0db9..24b931232eb2 100644
> --- a/drivers/base/firmware.c
> +++ b/drivers/base/firmware.c
> @@ -11,6 +11,7 @@
>   #include <linux/module.h>
>   #include <linux/init.h>
>   #include <linux/device.h>
> +#include <linux/firmware_bootinfo.h>
>   
>   #include "base.h"
>   
> @@ -24,3 +25,92 @@ int __init firmware_init(void)
>   		return -ENOMEM;
>   	return 0;
>   }
> +
> +/*
> + * Exposes attributes documented in Documentation/ABI/testing/sysfs-firmware-bootinfo
> + */
> +static struct bootinfo bootinfo;
> +
> +static ssize_t abr_image_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.abr_image.val);
> +}
> +static DEVICE_ATTR_RO(abr_image);
> +
> +static ssize_t low_security_key_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.low_security_key.val);
> +}
> +static DEVICE_ATTR_RO(low_security_key);
> +
> +static ssize_t otp_protected_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.otp_protected.val);
> +}
> +static DEVICE_ATTR_RO(otp_protected);
> +
> +static ssize_t secure_boot_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.secure_boot.val);
> +}
> +static DEVICE_ATTR_RO(secure_boot);
> +
> +static ssize_t uart_boot_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", bootinfo.uart_boot.val);
> +}
> +static DEVICE_ATTR_RO(uart_boot);
> +
> +#define ATTR_ENABLED(a) ((attr == &dev_attr_##a.attr) && bootinfo.a.en)
> +
> +static umode_t bootinfo_attr_mode(struct kobject *kobj, struct attribute *attr, int index)
> +{
> +	if (ATTR_ENABLED(abr_image))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(otp_protected))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(low_security_key))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(otp_protected))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(low_security_key))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(secure_boot))
> +		return 0444;
> +
> +	if (ATTR_ENABLED(uart_boot))
> +		return 0444;
> +
> +	return 0;
> +}
> +
> +static struct attribute *bootinfo_attrs[] = {
> +	&dev_attr_abr_image.attr,
> +	&dev_attr_low_security_key.attr,
> +	&dev_attr_otp_protected.attr,
> +	&dev_attr_secure_boot.attr,
> +	&dev_attr_uart_boot.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group bootinfo_attr_group = {
> +	.attrs = bootinfo_attrs,
> +	.is_visible = bootinfo_attr_mode,
> +};
> +
> +int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init)
> +{
> +	struct kobject *kobj = kobject_create_and_add("bootinfo", firmware_kobj);
> +	if (!kobj)
> +		return -ENOMEM;
> +
> +	memcpy(&bootinfo, bootinfo_init, sizeof(bootinfo));
> +
> +	return sysfs_create_group(kobj, &bootinfo_attr_group);
> +}
> +EXPORT_SYMBOL_GPL(firmware_bootinfo_init);
> diff --git a/include/linux/firmware_bootinfo.h b/include/linux/firmware_bootinfo.h
> new file mode 100644
> index 000000000000..3fe630b061b9
> --- /dev/null
> +++ b/include/linux/firmware_bootinfo.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/* Copyright 2022 IBM Corp. */
> +
> +#include <linux/sysfs.h>
> +#include <linux/init.h>
> +
> +#define BOOTINFO_SET(b, n, v) b.n.en = true; b.n.val = v
> +
> +struct bootinfo_entry {
> +	bool en;
> +	bool val;
> +};
> +
> +struct bootinfo {
> +	struct bootinfo_entry abr_image;
> +	struct bootinfo_entry low_security_key;
> +	struct bootinfo_entry otp_protected;
> +	struct bootinfo_entry secure_boot;
> +	struct bootinfo_entry uart_boot;
> +};
> +
> +int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init);
Joel Stanley Feb. 4, 2022, 5:53 a.m. UTC | #3 
On Thu, 3 Feb 2022 at 14:23, Robin Murphy <robin.murphy@arm.com> wrote:
> > diff --git a/Documentation/ABI/testing/sysfs-firmware-bootinfo b/Documentation/ABI/testing/sysfs-firmware-bootinfo
> > new file mode 100644
> > index 000000000000..cd6c42316345
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-firmware-bootinfo
> > @@ -0,0 +1,43 @@
> > +What:                /sys/firmware/bootinfo/*
> > +Date:                Jan 2022
> > +Description:
> > +             A system can expose information about how it was started in
> > +             this directory.
> > +
> > +             This information is agnostic as to the firmware implementation.
> > +
> > +             A system may expose a subset of these properties as applicable.
> > +
> > +
> > +What:                /sys/firmware/bootinfo/secure_boot
> > +Date:                Jan 2022
> > +Description:
> > +             Indicates the system was started with secure boot enabled in
> > +             the firmware.
> > +
> > +
> > +What:                /sys/firmware/bootinfo/abr_image
> > +Date:                Jan 2022
> > +Description:
> > +             Indicates the system was started from the alternate image
> > +             loaded from an Alternate Boot Region. Often this is a result of
> > +             the primary firmware image failing to start the system.
> > +
> > +
> > +What:                /sys/firmware/bootinfo/low_security_key
> > +Date:                Jan 2022
> > +Description:
> > +             Indicates the system's secure boot was verified with a low
> > +             security or development key.
> > +
> > +What:                /sys/firmware/bootinfo/otp_protected
> > +Date:                Jan 2022
> > +Description:
> > +             Indicates the system's boot configuration region is write
> > +             protected and cannot be modified.
> > +
> > +What:                /sys/firmware/bootinfo/uart_boot
> > +Date:                Jan 2022
> > +Description:
> > +             Indicates the system firmware was loaded from a UART instead of
> > +             an internal boot device.
>
> I'd be concerned about how well details like "uart_boot" and "abr_image"
> scale beyond one SoC family from one vendor. The combinatorial explosion
> of possible boot configurations across Linux-capable SoCs and firmware
> in general is larger than I'd care to imagine, even before considering
> that the nuances don't necessarily stop there - e.g. whether a given
> storage interface is hard-wired or user-accessible is not a fixed
> property on many SoCs, and even a socketed SD card might be "trusted" if
> a board is deployed in a product with a sealed enclosure.

This is a fair point. The first iteration of this idea was specific to
the aspeed soc.

For the system I'm building, secure_boot and otp_locked tell our
manufacturing test process that the machine has been correctly
provisioned. I'd like to get something agreed upon so we can start
using those sysfs files in the testing without having to go back and
change things.

abr_image is an indication that something went wrong at boot time. I
thought this was a standard eMMC concept, but taking a closer look
it's specific to the aspeed soc.

Would it help if we gave them generic names?

 - abr_image -> alternate_boot

I welcome other suggestions.

I'll drop the uart_boot property for now.

Cheers,

Joel
Joel Stanley Feb. 4, 2022, 6:55 a.m. UTC | #4 
On Thu, 3 Feb 2022 at 12:44, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Thu, Feb 03, 2022 at 10:23:42PM +1030, Joel Stanley wrote:

> > diff --git a/include/linux/firmware_bootinfo.h b/include/linux/firmware_bootinfo.h
> > new file mode 100644
> > index 000000000000..3fe630b061b9
> > --- /dev/null
> > +++ b/include/linux/firmware_bootinfo.h
> > @@ -0,0 +1,22 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
>
> I have to ask, do you really mean "or later"?

Yeah. That's what we're told we should use.

> > +/* Copyright 2022 IBM Corp. */
> > +
> > +#include <linux/sysfs.h>
> > +#include <linux/init.h>
> > +
> > +#define BOOTINFO_SET(b, n, v) b.n.en = true; b.n.val = v
>
> Please use a while {} loop around these two statements.
>
> Didn't checkpatch warn you about that?

No, it didn't. I'll add it.

>
> > +struct bootinfo_entry {
> > +     bool en;
>
> What does "en" mean?  "enabled"?  If so, please spell it out.
>
> > +     bool val;
>
> How can a "value" have a boolean?  Is this "valid"?  Again, please spell
> it out, we have no lack of letters to use here to keep people from being
> confused.

I meant value. I think it's reasonable for a value to be true or
false. I'll make the names clearer with docs as you suggest.

>
> Can you please use kernel-doc comments to describe this structure?
>
>
> > +};
> > +
> > +struct bootinfo {
> > +     struct bootinfo_entry abr_image;
> > +     struct bootinfo_entry low_security_key;
> > +     struct bootinfo_entry otp_protected;
> > +     struct bootinfo_entry secure_boot;
> > +     struct bootinfo_entry uart_boot;
> > +};
>
> Same here, please use kernel-doc
>
> > +
> > +int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init);
>
> __init is not needed on a function definition like this.

ack.
Daniel Axtens Feb. 7, 2022, 6:39 a.m. UTC | #5 
Hi,

I really like this design.

Currently on powerpc, a user wanting to check if firmware was
configured to boot with secure boot has to understand both OpenPower
and PowerVM secure boot. On OpenPower they need to check for the
presence of a device-tree property. If they're on PowerVM they need to
decode a different device-tree property and check it's 2 or
greater. Of course, it's not stored as ASCII, it's \x02. And it's
stored big-endian too.

So if powerpc implemented this infrastructure, it would provide users
with one single place to look, and it would represent the value as
ASCII. All very lovely, and it would simplify some scripts enormously.

Reviewed-by: Daniel Axtens <dja@axtens.net>

Kind regards,
Daniel
diff mbox series

Patch

diff --git a/Documentation/ABI/testing/sysfs-firmware-bootinfo b/Documentation/ABI/testing/sysfs-firmware-bootinfo
new file mode 100644
index 000000000000..cd6c42316345
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-firmware-bootinfo
@@ -0,0 +1,43 @@ 
+What:		/sys/firmware/bootinfo/*
+Date:		Jan 2022
+Description:
+		A system can expose information about how it was started in
+		this directory.
+
+		This information is agnostic as to the firmware implementation.
+
+		A system may expose a subset of these properties as applicable.
+
+
+What:		/sys/firmware/bootinfo/secure_boot
+Date:		Jan 2022
+Description:
+		Indicates the system was started with secure boot enabled in
+		the firmware.
+
+
+What:		/sys/firmware/bootinfo/abr_image
+Date:		Jan 2022
+Description:
+		Indicates the system was started from the alternate image
+		loaded from an Alternate Boot Region. Often this is a result of
+		the primary firmware image failing to start the system.
+
+
+What:		/sys/firmware/bootinfo/low_security_key
+Date:		Jan 2022
+Description:
+		Indicates the system's secure boot was verified with a low
+		security or development key.
+
+What:		/sys/firmware/bootinfo/otp_protected
+Date:		Jan 2022
+Description:
+		Indicates the system's boot configuration region is write
+		protected and cannot be modified.
+
+What:		/sys/firmware/bootinfo/uart_boot
+Date:		Jan 2022
+Description:
+		Indicates the system firmware was loaded from a UART instead of
+		an internal boot device.
diff --git a/drivers/base/firmware.c b/drivers/base/firmware.c
index 8dff940e0db9..24b931232eb2 100644
--- a/drivers/base/firmware.c
+++ b/drivers/base/firmware.c
@@ -11,6 +11,7 @@ 
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/device.h>
+#include <linux/firmware_bootinfo.h>
 
 #include "base.h"
 
@@ -24,3 +25,92 @@  int __init firmware_init(void)
 		return -ENOMEM;
 	return 0;
 }
+
+/*
+ * Exposes attributes documented in Documentation/ABI/testing/sysfs-firmware-bootinfo
+ */
+static struct bootinfo bootinfo;
+
+static ssize_t abr_image_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", bootinfo.abr_image.val);
+}
+static DEVICE_ATTR_RO(abr_image);
+
+static ssize_t low_security_key_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", bootinfo.low_security_key.val);
+}
+static DEVICE_ATTR_RO(low_security_key);
+
+static ssize_t otp_protected_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", bootinfo.otp_protected.val);
+}
+static DEVICE_ATTR_RO(otp_protected);
+
+static ssize_t secure_boot_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", bootinfo.secure_boot.val);
+}
+static DEVICE_ATTR_RO(secure_boot);
+
+static ssize_t uart_boot_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", bootinfo.uart_boot.val);
+}
+static DEVICE_ATTR_RO(uart_boot);
+
+#define ATTR_ENABLED(a) ((attr == &dev_attr_##a.attr) && bootinfo.a.en)
+
+static umode_t bootinfo_attr_mode(struct kobject *kobj, struct attribute *attr, int index)
+{
+	if (ATTR_ENABLED(abr_image))
+		return 0444;
+
+	if (ATTR_ENABLED(otp_protected))
+		return 0444;
+
+	if (ATTR_ENABLED(low_security_key))
+		return 0444;
+
+	if (ATTR_ENABLED(otp_protected))
+		return 0444;
+
+	if (ATTR_ENABLED(low_security_key))
+		return 0444;
+
+	if (ATTR_ENABLED(secure_boot))
+		return 0444;
+
+	if (ATTR_ENABLED(uart_boot))
+		return 0444;
+
+	return 0;
+}
+
+static struct attribute *bootinfo_attrs[] = {
+	&dev_attr_abr_image.attr,
+	&dev_attr_low_security_key.attr,
+	&dev_attr_otp_protected.attr,
+	&dev_attr_secure_boot.attr,
+	&dev_attr_uart_boot.attr,
+	NULL,
+};
+
+static const struct attribute_group bootinfo_attr_group = {
+	.attrs = bootinfo_attrs,
+	.is_visible = bootinfo_attr_mode,
+};
+
+int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init)
+{
+	struct kobject *kobj = kobject_create_and_add("bootinfo", firmware_kobj);
+	if (!kobj)
+		return -ENOMEM;
+
+	memcpy(&bootinfo, bootinfo_init, sizeof(bootinfo));
+
+	return sysfs_create_group(kobj, &bootinfo_attr_group);
+}
+EXPORT_SYMBOL_GPL(firmware_bootinfo_init);
diff --git a/include/linux/firmware_bootinfo.h b/include/linux/firmware_bootinfo.h
new file mode 100644
index 000000000000..3fe630b061b9
--- /dev/null
+++ b/include/linux/firmware_bootinfo.h
@@ -0,0 +1,22 @@ 
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright 2022 IBM Corp. */
+
+#include <linux/sysfs.h>
+#include <linux/init.h>
+
+#define BOOTINFO_SET(b, n, v) b.n.en = true; b.n.val = v
+
+struct bootinfo_entry {
+	bool en;
+	bool val;
+};
+
+struct bootinfo {
+	struct bootinfo_entry abr_image;
+	struct bootinfo_entry low_security_key;
+	struct bootinfo_entry otp_protected;
+	struct bootinfo_entry secure_boot;
+	struct bootinfo_entry uart_boot;
+};
+
+int __init firmware_bootinfo_init(struct bootinfo *bootinfo_init);