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![Tyler Hicks](/assets/img/avatar_default.png)
Require that the TCG_PCR_EVENT2.digests.count value strictly matches the
value of TCG_EfiSpecIdEvent.numberOfAlgorithms in the event field of the
TCG_PCClientPCREvent event log header. Also require that
TCG_EfiSpecIdEvent.numberOfAlgorithms is non-zero.
The TCG PC Client Platform Firmware Profile Specification section 9.1
(Family "2.0", Level 00 Revision 1.04) states:
For each Hash algorithm enumerated in the TCG_PCClientPCREvent entry,
there SHALL be a corresponding digest in all TCG_PCR_EVENT2 structures.
Note: This includes EV_NO_ACTION events which do not extend the PCR.
Section 9.4.5.1 provides this description of
TCG_EfiSpecIdEvent.numberOfAlgorithms:
The number of Hash algorithms in the digestSizes field. This field MUST
be set to a value of 0x01 or greater.
Enforce these restrictions, as required by the above specification, in
order to better identify and ignore invalid sequences of bytes at the
end of an otherwise valid TPM2 event log. Firmware doesn't always have
the means necessary to inform the kernel of the actual event log size so
the kernel's event log parsing code should be stringent when parsing the
event log for resiliency against firmware bugs. This is true, for
example, when firmware passes the event log to the kernel via a reserved
memory region described in device tree.
POWER and some ARM systems use the "linux,sml-base" and "linux,sml-size"
device tree properties to describe the memory region used to pass the
event log from firmware to the kernel. Unfortunately, the
"linux,sml-size" property describes the size of the entire reserved
memory region rather than the size of the event long within the memory
region and the event log format does not include information describing
the size of the event log.
tpm_read_log_of(), in drivers/char/tpm/eventlog/of.c, is where the
"linux,sml-size" property is used. At the end of that function,
log->bios_event_log_end is pointing at the end of the reserved memory
region. That's typically 0x10000 bytes offset from "linux,sml-base",
depending on what's defined in the device tree source.
The firmware event log only fills a portion of those 0x10000 bytes and
the rest of the memory region should be zeroed out by firmware. Even in
the case of a properly zeroed bytes in the remainder of the memory
region, the only thing allowing the kernel's event log parser to detect
the end of the event log is the following conditional in
__calc_tpm2_event_size():
if (event_type == 0 && event_field->event_size == 0)
size = 0;
If that wasn't there, __calc_tpm2_event_size() would think that a 16
byte sequence of zeroes, following an otherwise valid event log, was
a valid event.
However, problems can occur if a single bit is set in the offset
corresponding to either the TCG_PCR_EVENT2.eventType or
TCG_PCR_EVENT2.eventSize fields, after the last valid event log entry.
This could confuse the parser into thinking that an additional entry is
present in the event log and exposing this invalid entry to userspace in
the /sys/kernel/security/tpm0/binary_bios_measurements file. Such
problems have been seen if firmware does not fully zero the memory
region upon a warm reboot.
This patch significantly raises the bar on how difficult it is for
stale/invalid memory to confuse the kernel's event log parser but
there's still, ultimately, a reliance on firmware to properly initialize
the remainder of the memory region reserved for the event log as the
parser cannot be expected to detect a stale but otherwise properly
formatted firmware event log entry.
Fixes: fd5c78694f
("tpm: fix handling of the TPM 2.0 event logs")
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
294 lines
6.5 KiB
C
294 lines
6.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_TPM_EVENTLOG_H__
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#define __LINUX_TPM_EVENTLOG_H__
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#include <linux/tpm.h>
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#define TCG_EVENT_NAME_LEN_MAX 255
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#define MAX_TEXT_EVENT 1000 /* Max event string length */
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#define ACPI_TCPA_SIG "TCPA" /* 0x41504354 /'TCPA' */
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#define EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2 0x1
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#define EFI_TCG2_EVENT_LOG_FORMAT_TCG_2 0x2
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#ifdef CONFIG_PPC64
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#define do_endian_conversion(x) be32_to_cpu(x)
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#else
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#define do_endian_conversion(x) x
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#endif
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enum bios_platform_class {
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BIOS_CLIENT = 0x00,
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BIOS_SERVER = 0x01,
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};
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struct tcpa_event {
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u32 pcr_index;
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u32 event_type;
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u8 pcr_value[20]; /* SHA1 */
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u32 event_size;
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u8 event_data[];
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};
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enum tcpa_event_types {
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PREBOOT = 0,
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POST_CODE,
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UNUSED,
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NO_ACTION,
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SEPARATOR,
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ACTION,
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EVENT_TAG,
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SCRTM_CONTENTS,
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SCRTM_VERSION,
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CPU_MICROCODE,
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PLATFORM_CONFIG_FLAGS,
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TABLE_OF_DEVICES,
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COMPACT_HASH,
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IPL,
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IPL_PARTITION_DATA,
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NONHOST_CODE,
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NONHOST_CONFIG,
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NONHOST_INFO,
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};
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struct tcpa_pc_event {
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u32 event_id;
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u32 event_size;
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u8 event_data[];
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};
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enum tcpa_pc_event_ids {
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SMBIOS = 1,
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BIS_CERT,
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POST_BIOS_ROM,
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ESCD,
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CMOS,
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NVRAM,
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OPTION_ROM_EXEC,
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OPTION_ROM_CONFIG,
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OPTION_ROM_MICROCODE = 10,
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S_CRTM_VERSION,
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S_CRTM_CONTENTS,
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POST_CONTENTS,
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HOST_TABLE_OF_DEVICES,
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};
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/* http://www.trustedcomputinggroup.org/tcg-efi-protocol-specification/ */
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struct tcg_efi_specid_event_algs {
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u16 alg_id;
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u16 digest_size;
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} __packed;
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#define TCG_SPECID_SIG "Spec ID Event03"
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struct tcg_efi_specid_event_head {
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u8 signature[16];
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u32 platform_class;
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u8 spec_version_minor;
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u8 spec_version_major;
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u8 spec_errata;
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u8 uintnsize;
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u32 num_algs;
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struct tcg_efi_specid_event_algs digest_sizes[];
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} __packed;
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struct tcg_pcr_event {
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u32 pcr_idx;
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u32 event_type;
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u8 digest[20];
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u32 event_size;
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u8 event[];
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} __packed;
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struct tcg_event_field {
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u32 event_size;
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u8 event[];
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} __packed;
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struct tcg_pcr_event2_head {
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u32 pcr_idx;
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u32 event_type;
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u32 count;
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struct tpm_digest digests[];
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} __packed;
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struct tcg_algorithm_size {
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u16 algorithm_id;
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u16 algorithm_size;
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};
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struct tcg_algorithm_info {
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u8 signature[16];
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u32 platform_class;
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u8 spec_version_minor;
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u8 spec_version_major;
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u8 spec_errata;
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u8 uintn_size;
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u32 number_of_algorithms;
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struct tcg_algorithm_size digest_sizes[];
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};
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#ifndef TPM_MEMREMAP
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#define TPM_MEMREMAP(start, size) NULL
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#endif
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#ifndef TPM_MEMUNMAP
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#define TPM_MEMUNMAP(start, size) do{} while(0)
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#endif
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/**
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* __calc_tpm2_event_size - calculate the size of a TPM2 event log entry
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* @event: Pointer to the event whose size should be calculated
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* @event_header: Pointer to the initial event containing the digest lengths
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* @do_mapping: Whether or not the event needs to be mapped
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*
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* The TPM2 event log format can contain multiple digests corresponding to
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* separate PCR banks, and also contains a variable length of the data that
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* was measured. This requires knowledge of how long each digest type is,
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* and this information is contained within the first event in the log.
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*
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* We calculate the length by examining the number of events, and then looking
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* at each event in turn to determine how much space is used for events in
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* total. Once we've done this we know the offset of the data length field,
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* and can calculate the total size of the event.
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*
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* Return: size of the event on success, 0 on failure
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*/
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static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
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struct tcg_pcr_event *event_header,
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bool do_mapping)
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{
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struct tcg_efi_specid_event_head *efispecid;
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struct tcg_event_field *event_field;
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void *mapping = NULL;
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int mapping_size;
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void *marker;
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void *marker_start;
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u32 halg_size;
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size_t size;
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u16 halg;
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int i;
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int j;
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u32 count, event_type;
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const u8 zero_digest[sizeof(event_header->digest)] = {0};
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marker = event;
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marker_start = marker;
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marker = marker + sizeof(event->pcr_idx) + sizeof(event->event_type)
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+ sizeof(event->count);
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/* Map the event header */
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if (do_mapping) {
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mapping_size = marker - marker_start;
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mapping = TPM_MEMREMAP((unsigned long)marker_start,
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mapping_size);
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if (!mapping) {
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size = 0;
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goto out;
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}
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} else {
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mapping = marker_start;
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}
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event = (struct tcg_pcr_event2_head *)mapping;
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/*
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* The loop below will unmap these fields if the log is larger than
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* one page, so save them here for reference:
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*/
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count = READ_ONCE(event->count);
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event_type = READ_ONCE(event->event_type);
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/* Verify that it's the log header */
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if (event_header->pcr_idx != 0 ||
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event_header->event_type != NO_ACTION ||
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memcmp(event_header->digest, zero_digest, sizeof(zero_digest))) {
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size = 0;
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goto out;
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}
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efispecid = (struct tcg_efi_specid_event_head *)event_header->event;
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/*
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* Perform validation of the event in order to identify malformed
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* events. This function may be asked to parse arbitrary byte sequences
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* immediately following a valid event log. The caller expects this
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* function to recognize that the byte sequence is not a valid event
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* and to return an event size of 0.
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*/
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if (memcmp(efispecid->signature, TCG_SPECID_SIG,
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sizeof(TCG_SPECID_SIG)) ||
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!efispecid->num_algs || count != efispecid->num_algs) {
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size = 0;
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goto out;
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}
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for (i = 0; i < count; i++) {
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halg_size = sizeof(event->digests[i].alg_id);
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/* Map the digest's algorithm identifier */
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if (do_mapping) {
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TPM_MEMUNMAP(mapping, mapping_size);
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mapping_size = halg_size;
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mapping = TPM_MEMREMAP((unsigned long)marker,
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mapping_size);
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if (!mapping) {
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size = 0;
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goto out;
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}
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} else {
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mapping = marker;
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}
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memcpy(&halg, mapping, halg_size);
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marker = marker + halg_size;
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for (j = 0; j < efispecid->num_algs; j++) {
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if (halg == efispecid->digest_sizes[j].alg_id) {
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marker +=
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efispecid->digest_sizes[j].digest_size;
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break;
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}
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}
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/* Algorithm without known length. Such event is unparseable. */
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if (j == efispecid->num_algs) {
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size = 0;
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goto out;
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}
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}
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/*
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* Map the event size - we don't read from the event itself, so
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* we don't need to map it
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*/
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if (do_mapping) {
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TPM_MEMUNMAP(mapping, mapping_size);
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mapping_size += sizeof(event_field->event_size);
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mapping = TPM_MEMREMAP((unsigned long)marker,
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mapping_size);
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if (!mapping) {
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size = 0;
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goto out;
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}
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} else {
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mapping = marker;
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}
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event_field = (struct tcg_event_field *)mapping;
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marker = marker + sizeof(event_field->event_size)
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+ event_field->event_size;
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size = marker - marker_start;
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if (event_type == 0 && event_field->event_size == 0)
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size = 0;
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out:
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if (do_mapping)
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TPM_MEMUNMAP(mapping, mapping_size);
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return size;
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}
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#endif
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