Re: [PATCH 1/2] efi: call get_event_log before ExitBootServices

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

Hi Thiebaud,

On 6 September 2017 at 15:25, Thiebaud Weksteen <tweek@google.com> wrote:
> With TPM 2.0, access to the event log is only possible by using the
> EFI TPM2 Boot Service. Modify the EFI stub to copy the log area to a new
> Linux-specific EFI table so it remains accessible for future use.
>
> Signed-off-by: Thiebaud Weksteen <tweek@google.com>
> ---
>  arch/x86/boot/compressed/eboot.c      |  1 +
>  drivers/char/tpm/tpm.h                | 29 ++++++++++---
>  drivers/char/tpm/tpm_eventlog.h       | 26 +++---------
>  drivers/firmware/efi/libstub/Makefile |  3 +-
>  drivers/firmware/efi/libstub/tpm.c    | 80 +++++++++++++++++++++++++++++++++++
>  include/linux/efi.h                   | 35 +++++++++++++++
>  6 files changed, 146 insertions(+), 28 deletions(-)
>

Why is this x86 only?


> diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> index a1686f3dc295..97bec8df36ff 100644
> --- a/arch/x86/boot/compressed/eboot.c
> +++ b/arch/x86/boot/compressed/eboot.c
> @@ -999,6 +999,7 @@ struct boot_params *efi_main(struct efi_config *c,
>
>         /* Ask the firmware to clear memory on unclean shutdown */
>         efi_enable_reset_attack_mitigation(sys_table);
> +       efi_retrieve_tpm2_eventlog(boot_params, sys_table);
>
>         setup_graphics(boot_params);
>
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 04fbff2edbf3..efede7dc9340 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -40,6 +40,8 @@
>  #include <asm/intel-family.h>
>  #endif
>
> +#include "tpm_eventlog.h"
> +
>  enum tpm_const {
>         TPM_MINOR = 224,        /* officially assigned */
>         TPM_BUFSIZE = 4096,
> @@ -397,11 +399,6 @@ struct tpm_cmd_t {
>         tpm_cmd_params  params;
>  } __packed;
>
> -struct tpm2_digest {
> -       u16 alg_id;
> -       u8 digest[SHA512_DIGEST_SIZE];
> -} __packed;
> -
>  /* A string buffer type for constructing TPM commands. This is based on the
>   * ideas of string buffer code in security/keys/trusted.h but is heap based
>   * in order to keep the stack usage minimal.
> @@ -581,4 +578,26 @@ int tpm2_prepare_space(struct tpm_chip *chip, struct tpm_space *space, u32 cc,
>                        u8 *cmd);
>  int tpm2_commit_space(struct tpm_chip *chip, struct tpm_space *space,
>                       u32 cc, u8 *buf, size_t *bufsiz);
> +
> +extern const struct seq_operations tpm2_binary_b_measurements_seqops;
> +
> +#if defined(CONFIG_ACPI)
> +int tpm_read_log_acpi(struct tpm_chip *chip);
> +#else
> +static inline int tpm_read_log_acpi(struct tpm_chip *chip)
> +{
> +       return -ENODEV;
> +}
> +#endif
> +#if defined(CONFIG_OF)
> +int tpm_read_log_of(struct tpm_chip *chip);
> +#else
> +static inline int tpm_read_log_of(struct tpm_chip *chip)
> +{
> +       return -ENODEV;
> +}
> +#endif
> +
> +int tpm_bios_log_setup(struct tpm_chip *chip);
> +void tpm_bios_log_teardown(struct tpm_chip *chip);
>  #endif
> diff --git a/drivers/char/tpm/tpm_eventlog.h b/drivers/char/tpm/tpm_eventlog.h
> index b4b549559203..1009a2503985 100644
> --- a/drivers/char/tpm/tpm_eventlog.h
> +++ b/drivers/char/tpm/tpm_eventlog.h
> @@ -104,6 +104,11 @@ struct tcg_event_field {
>         u8 event[0];
>  } __packed;
>
> +struct tpm2_digest {
> +       u16 alg_id;
> +       u8 digest[SHA512_DIGEST_SIZE];
> +} __packed;
> +
>  struct tcg_pcr_event2 {
>         u32 pcr_idx;
>         u32 event_type;
> @@ -112,26 +117,5 @@ struct tcg_pcr_event2 {
>         struct tcg_event_field event;
>  } __packed;
>
> -extern const struct seq_operations tpm2_binary_b_measurements_seqops;
> -
> -#if defined(CONFIG_ACPI)
> -int tpm_read_log_acpi(struct tpm_chip *chip);
> -#else
> -static inline int tpm_read_log_acpi(struct tpm_chip *chip)
> -{
> -       return -ENODEV;
> -}
> -#endif
> -#if defined(CONFIG_OF)
> -int tpm_read_log_of(struct tpm_chip *chip);
> -#else
> -static inline int tpm_read_log_of(struct tpm_chip *chip)
> -{
> -       return -ENODEV;
> -}
> -#endif
> -
> -int tpm_bios_log_setup(struct tpm_chip *chip);
> -void tpm_bios_log_teardown(struct tpm_chip *chip);
>
>  #endif
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index dedf9bde44db..2abe6d22dc5f 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -29,8 +29,7 @@ OBJECT_FILES_NON_STANDARD     := y
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
>  KCOV_INSTRUMENT                        := n
>
> -lib-y                          := efi-stub-helper.o gop.o secureboot.o
> -lib-$(CONFIG_RESET_ATTACK_MITIGATION) += tpm.o
> +lib-y                          := efi-stub-helper.o gop.o secureboot.o tpm.o
>

Did you build test on ARM/arm64 as well?

>  # include the stub's generic dependencies from lib/ when building for ARM/arm64
>  arm-deps := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c sort.c
> diff --git a/drivers/firmware/efi/libstub/tpm.c b/drivers/firmware/efi/libstub/tpm.c
> index 6224cdbc9669..ba2cb68833fb 100644
> --- a/drivers/firmware/efi/libstub/tpm.c
> +++ b/drivers/firmware/efi/libstub/tpm.c
> @@ -4,6 +4,7 @@
>   * Copyright (C) 2016 CoreOS, Inc
>   * Copyright (C) 2017 Google, Inc.
>   *     Matthew Garrett <mjg59@google.com>
> + *     Thiebaud Weksteen <tweek@google.com>
>   *
>   * This file is part of the Linux kernel, and is made available under the
>   * terms of the GNU General Public License version 2.
> @@ -12,7 +13,9 @@
>  #include <asm/efi.h>
>
>  #include "efistub.h"
> +#include "../../../char/tpm/tpm_eventlog.h"
>
> +#if IS_ENABLED(CONFIG_RESET_ATTACK_MITIGATION)

IS_ENABLED() is intended for C style if()s rather than preprocessor
conditionals. Please replace with #ifdef

>  static const efi_char16_t efi_MemoryOverWriteRequest_name[] = {
>         'M', 'e', 'm', 'o', 'r', 'y', 'O', 'v', 'e', 'r', 'w', 'r', 'i', 't',
>         'e', 'R', 'e', 'q', 'u', 'e', 's', 't', 'C', 'o', 'n', 't', 'r', 'o',
> @@ -56,3 +59,80 @@ void efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg)
>                     EFI_VARIABLE_BOOTSERVICE_ACCESS |
>                     EFI_VARIABLE_RUNTIME_ACCESS, sizeof(val), &val);
>  }
> +
> +#endif
> +
> +void efi_retrieve_tpm2_eventlog_1_2(struct boot_params *boot_params,

Does this function actually use struct boot_params?

> +                                   efi_system_table_t *sys_table_arg)
> +{
> +       efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
> +       efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
> +       efi_status_t status;
> +       efi_physical_addr_t log_location, log_last_entry;
> +       struct linux_efi_tpm_eventlog *log_tbl;
> +       size_t log_size, last_entry_size;
> +       efi_bool_t truncated;
> +       void *tcg2_protocol;
> +
> +       status = efi_call_early(locate_protocol, &tcg2_guid, NULL,
> +                       &tcg2_protocol);

Please indent appropriately.

> +       if (status != EFI_SUCCESS)
> +               return;
> +
> +       status = efi_call_proto(efi_tcg2_protocol, get_event_log, tcg2_protocol,
> +                               EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2,
> +                               &log_location, &log_last_entry, &truncated);
> +       if (status != EFI_SUCCESS)
> +               return;
> +
> +       if (!log_location)
> +               return;
> +
> +       /*
> +        * If the logs are empty, we still populate the EFI table to surface

I am not a native English speaker, but 'to surface' sounds a bit awkward here.

> +        * this information to userland.
> +        */
> +       if (!log_last_entry) {
> +               log_size = 0;
> +       } else {
> +               /*
> +                * get_event_log only returns the address of the last entry.
> +                * We need to calculate its size to deduce the full size of
> +                * the logs.
> +                */
> +               last_entry_size = sizeof(struct tcpa_event) +
> +                       ((struct tcpa_event *)log_last_entry)->event_size;
> +               log_size = log_last_entry - log_location + last_entry_size;
> +       }
> +
> +       /* Allocate space for the logs and copy them. */
> +       status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,

Why is this runtime services data? You are passing your own data
across the UEFI / kernel handover, and so if you parse your config
table early enough, you can just reserve this memory.

Runtime services data will be given a virtual mapping by the firmware
so it is accessible to the firmware itself during runtime services
invocations, and on ARM/arm64, we actually have to omit if from the
ordinary direct mapping of memory, which may lead to page table
fragmentation and increased TLB pressure.

In summary, don't use it as a convenience so you don'y have to think
about when/how to reserve it from normal allocation by the kernel.

> +                               sizeof(*log_tbl) + log_size, &log_tbl);
> +
> +       if (status != EFI_SUCCESS) {
> +               efi_printk(sys_table_arg,
> +                          "Unable to allocate memory for event log\n");
> +               return;
> +       }
> +
> +       memset(log_tbl, 0, sizeof(*log_tbl) + log_size);
> +       log_tbl->size = log_size;
> +       log_tbl->version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2;
> +       memcpy(log_tbl->log, (void *)log_location, log_size);
> +
> +       status = efi_call_early(install_configuration_table,
> +                       &linux_eventlog_guid, log_tbl);

Indentation please.

> +       if (status != EFI_SUCCESS)
> +               goto err_free;
> +       return;
> +
> +err_free:
> +       efi_call_early(free_pool, log_tbl);
> +}
> +
> +void efi_retrieve_tpm2_eventlog(struct boot_params *boot_params,
> +                               efi_system_table_t *sys_table_arg)
> +{
> +       /* Only try to retrieve the logs in 1.2 format. */
> +       efi_retrieve_tpm2_eventlog_1_2(boot_params, sys_table_arg);
> +}
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 8dc3d94a3e3c..5eaaa68ac58a 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -472,6 +472,26 @@ typedef struct {
>         u64 get_all;
>  } apple_properties_protocol_64_t;
>
> +typedef struct {
> +       u32 get_capability;
> +       u32 get_event_log;
> +       u32 hash_log_extend_event;
> +       u32 submit_command;
> +       u32 get_active_pcr_banks;
> +       u32 set_active_pcr_banks;
> +       u32 get_result_of_set_active_pcr_banks;
> +} efi_tcg2_protocol_32_t;
> +
> +typedef struct {
> +       u64 get_capability;
> +       u64 get_event_log;
> +       u64 hash_log_extend_event;
> +       u64 submit_command;
> +       u64 get_active_pcr_banks;
> +       u64 set_active_pcr_banks;
> +       u64 get_result_of_set_active_pcr_banks;
> +} efi_tcg2_protocol_64_t;
> +
>  /*
>   * Types and defines for EFI ResetSystem
>   */
> @@ -622,6 +642,7 @@ void efi_native_runtime_setup(void);
>  #define EFI_MEMORY_ATTRIBUTES_TABLE_GUID       EFI_GUID(0xdcfa911d, 0x26eb, 0x469f,  0xa2, 0x20, 0x38, 0xb7, 0xdc, 0x46, 0x12, 0x20)
>  #define EFI_CONSOLE_OUT_DEVICE_GUID            EFI_GUID(0xd3b36f2c, 0xd551, 0x11d4,  0x9a, 0x46, 0x00, 0x90, 0x27, 0x3f, 0xc1, 0x4d)
>  #define APPLE_PROPERTIES_PROTOCOL_GUID         EFI_GUID(0x91bd12fe, 0xf6c3, 0x44fb,  0xa5, 0xb7, 0x51, 0x22, 0xab, 0x30, 0x3a, 0xe0)
> +#define EFI_TCG2_PROTOCOL_GUID                 EFI_GUID(0x607f766c, 0x7455, 0x42be,  0x93, 0x0b, 0xe4, 0xd7, 0x6d, 0xb2, 0x72, 0x0f)
>
>  #define EFI_IMAGE_SECURITY_DATABASE_GUID       EFI_GUID(0xd719b2cb, 0x3d3a, 0x4596,  0xa3, 0xbc, 0xda, 0xd0, 0x0e, 0x67, 0x65, 0x6f)
>  #define EFI_SHIM_LOCK_GUID                     EFI_GUID(0x605dab50, 0xe046, 0x4300,  0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 0x23)
> @@ -634,6 +655,7 @@ void efi_native_runtime_setup(void);
>  #define LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID   EFI_GUID(0xe03fc20a, 0x85dc, 0x406e,  0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
>  #define LINUX_EFI_LOADER_ENTRY_GUID            EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf,  0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f)
>  #define LINUX_EFI_RANDOM_SEED_TABLE_GUID       EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2,  0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b)
> +#define LINUX_EFI_TPM_EVENT_LOG_GUID           EFI_GUID(0xb7799cb0, 0xeca2, 0x4943,  0x96, 0x67, 0x1f, 0xae, 0x07, 0xb7, 0x47, 0xfa)
>
>  typedef struct {
>         efi_guid_t guid;
> @@ -1504,6 +1526,9 @@ static inline void
>  efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg) { }
>  #endif
>
> +void efi_retrieve_tpm2_eventlog(struct boot_params *boot_params,
> +                               efi_system_table_t *sys_table);
> +
>  /*
>   * Arch code can implement the following three template macros, avoiding
>   * reptition for the void/non-void return cases of {__,}efi_call_virt():
> @@ -1571,4 +1596,14 @@ struct linux_efi_random_seed {
>         u8      bits[];
>  };
>
> +
> +#define EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2 0x1
> +#define EFI_TCG2_EVENT_LOG_FORMAT_TCG_2   0x2
> +
> +struct linux_efi_tpm_eventlog {
> +       u32     size;
> +       u8      version;
> +       u8      log[];
> +};
> +
>  #endif /* _LINUX_EFI_H */
> --
> 2.14.1.581.gf28d330327-goog
>
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