Message-ID: <CAKv+Gu8fX7x1x3Od5ThxyFxux_NKDx59PNedkgSfn_V0yg_NQQ@mail.gmail.com>
Date:	Mon, 21 Mar 2016 11:19:50 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	joeyli <jlee@...e.com>,
	Kweh Hock Leong <hock.leong.kweh@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Mark Salter <msalter@...hat.com>,
	Peter Jones <pjones@...hat.com>,
	"Bryan O'Donoghue" <pure.logic@...us-software.ie>
Subject: Re: [PATCH 2/4] efi: Capsule update support

On 17 March 2016 at 13:57, Matt Fleming <matt@...eblueprint.co.uk> wrote:
> The EFI capsule mechanism allows data blobs to be passed to the EFI
> firmware. A common use case is performing firmware updates. This patch
> just introduces the main infrastructure for interacting with the
> firmware, and a driver that allows users to upload capsules will come
> in a later patch.
>
> Once a capsule has been passed to the firmware, the next reboot must
> be performed using the ResetSystem() EFI runtime service, which may
> involve overriding the reboot type specified by reboot=. This ensures
> the reset value returned by QueryCapsuleCapabilities() is used to
> reset the system, which is required for the capsule to be processed.
> efi_capsule_pending() is provided for this purpose.
>
> At the moment we only allow a single capsule blob to be sent to the
> firmware despite the fact that UpdateCapsule() takes a 'CapsuleCount'
> parameter. This simplifies the API and shouldn't result in any
> downside since it is still possible to send multiple capsules by
> repeatedly calling UpdateCapsule().
>
> Cc: Kweh Hock Leong <hock.leong.kweh@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Mark Salter <msalter@...hat.com>
> Cc: Peter Jones <pjones@...hat.com>
> Cc: joeyli <jlee@...e.com>
> Cc: Bryan O'Donoghue <pure.logic@...us-software.ie>
> Signed-off-by: Matt Fleming <matt@...eblueprint.co.uk>

How are capsules with the CAPSULE_FLAGS_INITIATE_RESET flag handled?
The runtime service will never return in that case, so I suppose we
need some explicit handling somewhere?

> ---
>  drivers/firmware/efi/Makefile  |   2 +-
>  drivers/firmware/efi/capsule.c | 286 +++++++++++++++++++++++++++++++++++++++++
>  drivers/firmware/efi/reboot.c  |  12 +-
>  include/linux/efi.h            |  14 ++
>  4 files changed, 312 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/firmware/efi/capsule.c
>
> diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> index 62e654f255f4..e4468c7c16b5 100644
> --- a/drivers/firmware/efi/Makefile
> +++ b/drivers/firmware/efi/Makefile
> @@ -9,7 +9,7 @@
>  #
>  KASAN_SANITIZE_runtime-wrappers.o      := n
>
> -obj-$(CONFIG_EFI)                      += efi.o vars.o reboot.o
> +obj-$(CONFIG_EFI)                      += efi.o vars.o reboot.o capsule.o
>  obj-$(CONFIG_EFI_VARS)                 += efivars.o
>  obj-$(CONFIG_EFI_ESRT)                 += esrt.o
>  obj-$(CONFIG_EFI_VARS_PSTORE)          += efi-pstore.o
> diff --git a/drivers/firmware/efi/capsule.c b/drivers/firmware/efi/capsule.c
> new file mode 100644
> index 000000000000..dac25208ad5e
> --- /dev/null
> +++ b/drivers/firmware/efi/capsule.c
> @@ -0,0 +1,286 @@
> +/*
> + * EFI capsule support.
> + *
> + * Copyright 2013 Intel Corporation; author Matt Fleming
> + *
> + * This file is part of the Linux kernel, and is made available under
> + * the terms of the GNU General Public License version 2.
> + */
> +
> +#define pr_fmt(fmt) "efi: " fmt
> +
> +#include <linux/slab.h>
> +#include <linux/mutex.h>
> +#include <linux/highmem.h>
> +#include <linux/efi.h>
> +#include <linux/vmalloc.h>
> +#include <asm/io.h>
> +
> +typedef struct {
> +       u64 length;
> +       u64 data;
> +} efi_capsule_block_desc_t;
> +
> +static bool capsule_pending;
> +static int efi_reset_type = -1;
> +
> +/*
> + * capsule_mutex serialises access to both capsule_pending and
> + * efi_reset_type.
> + */
> +static DEFINE_MUTEX(capsule_mutex);
> +
> +/**
> + * efi_capsule_pending - has a capsule been passed to the firmware?
> + * @reset_type: store the type of EFI reset if capsule is pending
> + *
> + * To ensure that the registered capsule is processed correctly by the
> + * firmware we need to perform a specific type of reset. If a capsule is
> + * pending return the reset type in @reset_type.
> + *
> + * This function will race with callers of efi_capsule_update(), for
> + * example, calling this function while somebody else is in
> + * efi_capsule_update() but hasn't reached efi_capsue_update_locked()
> + * will miss the updates to capsule_pending and efi_reset_type after
> + * efi_capsule_update_locked() completes.
> + *
> + * A non-racy use is from platform reboot code because we use
> + * system_state to ensure no capsules can be sent to the firmware once
> + * we're at SYSTEM_RESTART. See efi_capsule_update_locked().
> + */
> +bool efi_capsule_pending(int *reset_type)
> +{
> +       bool rv = false;
> +
> +       mutex_lock(&capsule_mutex);
> +       if (!capsule_pending)
> +               goto out;
> +
> +       if (reset_type)
> +               *reset_type = efi_reset_type;
> +       rv = true;
> +out:
> +       mutex_unlock(&capsule_mutex);
> +       return rv;
> +}
> +
> +/**
> + * efi_capsule_supported - does the firmware support the capsule?
> + * @guid: vendor guid of capsule
> + * @flags: capsule flags
> + * @size: size of capsule data
> + * @reset: the reset type required for this capsule
> + *
> + * Check whether a capsule with @flags is supported by the firmware
> + * and that @size doesn't exceed the maximum size for a capsule.
> + *
> + * No attempt is made to check @reset against the reset type required
> + * by any pending capsules because of the races involved.
> + */
> +int efi_capsule_supported(efi_guid_t guid, u32 flags, size_t size, int *reset)
> +{
> +       efi_capsule_header_t *capsule;
> +       efi_status_t status;
> +       u64 max_size;
> +       int rv = 0;
> +
> +       capsule = kmalloc(sizeof(*capsule), GFP_KERNEL);
> +       if (!capsule)
> +               return -ENOMEM;
> +
> +       capsule->headersize = capsule->imagesize = sizeof(*capsule);
> +       memcpy(&capsule->guid, &guid, sizeof(efi_guid_t));
> +       capsule->flags = flags;
> +
> +       status = efi.query_capsule_caps(&capsule, 1, &max_size, reset);
> +       if (status != EFI_SUCCESS) {
> +               rv = efi_status_to_err(status);
> +               goto out;
> +       }
> +
> +       if (size > max_size)
> +               rv = -ENOSPC;
> +out:
> +       kfree(capsule);
> +       return rv;
> +}
> +EXPORT_SYMBOL_GPL(efi_capsule_supported);
> +
> +/*
> + * Every scatter gather list (block descriptor) page must end with a
> + * continuation pointer. The last continuation pointer of the last
> + * page must be zero to mark the end of the chain.
> + */
> +#define SGLIST_PER_PAGE        ((PAGE_SIZE / sizeof(efi_capsule_block_desc_t)) - 1)
> +
> +/*
> + * How many scatter gather list (block descriptor) pages do we need
> + * to map @count pages?
> + */
> +static inline unsigned int sg_pages_num(unsigned int count)
> +{
> +       return DIV_ROUND_UP(count, SGLIST_PER_PAGE);
> +}
> +
> +/**
> + * efi_capsule_update_locked - pass a single capsule to the firmware
> + * @capsule: capsule to send to the firmware
> + * @sg_pages: array of scatter gather (block descriptor) pages
> + * @reset: the reset type required for @capsule
> + *
> + * Since this function must be called under capsule_mutex check
> + * whether efi_reset_type will conflict with @reset, and atomically
> + * set it and capsule_pending if a capsule was successfully sent to
> + * the firmware.
> + *
> + * We also check to see if the system is about to restart, and if so,
> + * abort. This avoids races between efi_capsule_update() and
> + * efi_capsule_pending().
> + */
> +static int
> +efi_capsule_update_locked(efi_capsule_header_t *capsule,
> +                         struct page **sg_pages, int reset)
> +{
> +       efi_physical_addr_t sglist_phys;
> +       efi_status_t status;
> +
> +       lockdep_assert_held(&capsule_mutex);
> +
> +       /*
> +        * If someone has already registered a capsule that requires a
> +        * different reset type, we're out of luck and must abort.
> +        */
> +       if (efi_reset_type >= 0 && efi_reset_type != reset) {
> +               pr_err("Conflicting capsule reset type %d (%d).\n",
> +                      reset, efi_reset_type);
> +               return -EINVAL;
> +       }
> +
> +       /*
> +        * If the system is getting ready to restart it may have
> +        * called efi_capsule_pending() to make decisions (such as
> +        * whether to force an EFI reboot), and we're racing against
> +        * that call. Abort in that case.
> +        */
> +       if (unlikely(system_state == SYSTEM_RESTART)) {
> +               pr_warn("Capsule update raced with reboot, aborting.\n");
> +               return -EINVAL;
> +       }
> +
> +       sglist_phys = page_to_phys(sg_pages[0]);
> +
> +       status = efi.update_capsule(&capsule, 1, sglist_phys);
> +       if (status == EFI_SUCCESS) {
> +               capsule_pending = true;
> +               efi_reset_type = reset;
> +       }
> +
> +       return efi_status_to_err(status);
> +}
> +
> +/**
> + * efi_capsule_update - send a capsule to the firmware
> + * @capsule: capsule to send to firmware
> + * @pages: an array of capsule data pages
> + *
> + * Build a scatter gather list with EFI capsule block descriptors to
> + * map the capsule described by @capsule with its data in @pages and
> + * send it to the firmware via the UpdateCapsule() runtime service.
> + *
> + * @capsule must be a virtual mapping of the first page in @pages
> + * (@pages[0]) in the kernel address space. That is, a
> + * capsule_header_t that describes the entire contents of the capsule
> + * must be at the start of the first data page.
> + *
> + * Even though this function will validate that the firmware supports
> + * the capsule guid, users will likely want to check that
> + * efi_capsule_supported() returns true before calling this function
> + * because it makes it easier to print helpful error messages.
> + *
> + * If the capsule is successfully submitted to the firmware, any
> + * subsequent calls to efi_capsule_pending() will return true. @pages
> + * must not be released or modified if this function returns
> + * successfully.
> + *
> + * Callers must be prepared for this function to fail, which can
> + * happen if we raced with system reboot or if there is already a
> + * pending capsule that has a reset type that conflicts with the one
> + * required by @capsule. Do NOT use efi_capsule_pending() to detect
> + * this conflict since that would be racy. Instead, submit the capsule
> + * to efi_capsule_update() and check the return value.
> + *
> + * Return 0 on success, a converted EFI status code on failure.
> + */
> +int efi_capsule_update(efi_capsule_header_t *capsule, struct page **pages)
> +{
> +       u32 imagesize = capsule->imagesize;
> +       efi_guid_t guid = capsule->guid;
> +       unsigned int count, sg_count;
> +       u32 flags = capsule->flags;
> +       struct page **sg_pages;
> +       int rv, reset_type;
> +       int i, j;
> +
> +       rv = efi_capsule_supported(guid, flags, imagesize, &reset_type);
> +       if (rv)
> +               return rv;
> +
> +       count = DIV_ROUND_UP(imagesize, PAGE_SIZE);
> +       sg_count = sg_pages_num(count);
> +
> +       sg_pages = kzalloc(sg_count * sizeof(*sg_pages), GFP_KERNEL);
> +       if (!sg_pages)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < sg_count; i++) {
> +               sg_pages[i] = alloc_page(GFP_KERNEL);
> +               if (!sg_pages[i]) {
> +                       rv = -ENOMEM;
> +                       goto out;
> +               }
> +       }
> +
> +       for (i = 0; i < sg_count; i++) {
> +               efi_capsule_block_desc_t *sglist;
> +
> +               sglist = kmap(sg_pages[i]);
> +               if (!sglist) {
> +                       rv = -ENOMEM;
> +                       goto out;
> +               }
> +
> +               for (j = 0; j < SGLIST_PER_PAGE && count > 0; j++) {
> +                       u64 sz = min_t(u64, imagesize, PAGE_SIZE);
> +
> +                       sglist[j].length = sz;
> +                       sglist[j].data = page_to_phys(*pages++);
> +
> +                       imagesize -= sz;
> +                       count--;
> +               }
> +
> +               /* Continuation pointer */
> +               sglist[j].length = 0;
> +
> +               if (i + 1 == sg_count)
> +                       sglist[j].data = 0;
> +               else
> +                       sglist[j].data = page_to_phys(sg_pages[i + 1]);
> +
> +               kunmap(sg_pages[i]);
> +       }
> +
> +       mutex_lock(&capsule_mutex);
> +       rv = efi_capsule_update_locked(capsule, sg_pages, reset_type);
> +       mutex_unlock(&capsule_mutex);
> +
> +out:
> +       for (i = 0; rv && i < sg_count; i++) {
> +               if (sg_pages[i])
> +                       __free_page(sg_pages[i]);
> +       }
> +
> +       kfree(sg_pages);
> +       return rv;
> +}
> +EXPORT_SYMBOL_GPL(efi_capsule_update);
> diff --git a/drivers/firmware/efi/reboot.c b/drivers/firmware/efi/reboot.c
> index 9c59d1c795d1..62ead9b9d871 100644
> --- a/drivers/firmware/efi/reboot.c
> +++ b/drivers/firmware/efi/reboot.c
> @@ -9,7 +9,8 @@ int efi_reboot_quirk_mode = -1;
>
>  void efi_reboot(enum reboot_mode reboot_mode, const char *__unused)
>  {
> -       int efi_mode;
> +       const char *str[] = { "cold", "warm", "shutdown", "platform" };
> +       int efi_mode, cap_reset_mode;
>
>         if (!efi_enabled(EFI_RUNTIME_SERVICES))
>                 return;
> @@ -30,6 +31,15 @@ void efi_reboot(enum reboot_mode reboot_mode, const char *__unused)
>         if (efi_reboot_quirk_mode != -1)
>                 efi_mode = efi_reboot_quirk_mode;
>
> +       if (efi_capsule_pending(&cap_reset_mode)) {
> +               if (efi_mode != cap_reset_mode)
> +                       printk(KERN_CRIT "efi: %s reset requested but pending "
> +                              "capsule update requires %s reset... Performing "
> +                              "%s reset.\n", str[efi_mode], str[cap_reset_mode],
> +                              str[cap_reset_mode]);
> +               efi_mode = cap_reset_mode;
> +       }
> +
>         efi.reset_system(efi_mode, EFI_SUCCESS, 0, NULL);
>  }
>
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 9c8aae0e3b51..a28053e71e99 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -124,6 +124,13 @@ typedef struct {
>  } efi_capsule_header_t;
>
>  /*
> + * EFI capsule flags
> + */
> +#define EFI_CAPSULE_PERSIST_ACROSS_RESET       0x00010000
> +#define EFI_CAPSULE_POPULATE_SYSTEM_TABLE      0x00020000
> +#define EFI_CAPSULE_INITIATE_RESET             0x00040000
> +
> +/*
>   * Allocation types for calls to boottime->allocate_pages.
>   */
>  #define EFI_ALLOCATE_ANY_PAGES         0
> @@ -1239,6 +1246,13 @@ int efivars_sysfs_init(void);
>  #define EFIVARS_DATA_SIZE_MAX 1024
>
>  #endif /* CONFIG_EFI_VARS */
> +extern bool efi_capsule_pending(int *reset_type);
> +
> +extern int efi_capsule_supported(efi_guid_t guid, u32 flags,
> +                                size_t size, int *reset);
> +
> +extern int efi_capsule_update(efi_capsule_header_t *capsule,
> +                             struct page **pages);
>
>  #ifdef CONFIG_EFI_RUNTIME_MAP
>  int efi_runtime_map_init(struct kobject *);
> --
> 2.6.2
>

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