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

Ard Biesheuvel
2017-09-06T14:53:37Z

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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