Messages in this thread Patch in this message | | | Date | Thu, 3 Feb 2022 14:22:59 +0000 | Subject | Re: [PATCH v2 1/3] firmware: Add boot information to sysfs | From | Robin Murphy <> |
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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);
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