| Message ID | 1481434533-3453-3-git-send-email-nayna@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sun, Dec 11, 2016 at 12:35:33AM -0500, Nayna Jain wrote: > Unlike the device driver support for TPM 1.2, the TPM 2.0 does > not support the securityfs pseudo files for displaying the > firmware event log. > > This patch enables support for providing the TPM 2.0 event log in > binary form. TPM 2.0 event log supports a crypto agile format that > records multiple digests, which is different from TPM 1.2. This > patch enables the tpm_bios_log_setup for TPM 2.0 and adds the > event log parser which understand the TPM 2.0 crypto agile format. > > Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> There is something fundamentally wrong in this commit. You must not allow this feature unless CONFIG_OF is set. It is the only interface where the supply path of the event log is well defined on platforms that include a TPM 2.0 chip. There's buch casts in the form '(char *) foo'. They should be '(char *)foo'. > --- > drivers/char/tpm/Makefile | 2 +- > .../char/tpm/{tpm_eventlog.c => tpm1_eventlog.c} | 35 ++-- > drivers/char/tpm/tpm2_eventlog.c | 203 +++++++++++++++++++++ > drivers/char/tpm/tpm_eventlog.h | 70 +++++++ > 4 files changed, 295 insertions(+), 15 deletions(-) > rename drivers/char/tpm/{tpm_eventlog.c => tpm1_eventlog.c} (95%) > create mode 100644 drivers/char/tpm/tpm2_eventlog.c > > diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile > index a05b1eb..3d386a8 100644 > --- a/drivers/char/tpm/Makefile > +++ b/drivers/char/tpm/Makefile > @@ -3,7 +3,7 @@ > # > obj-$(CONFIG_TCG_TPM) += tpm.o > tpm-y := tpm-interface.o tpm-dev.o tpm-sysfs.o tpm-chip.o tpm2-cmd.o \ > - tpm_eventlog.o > + tpm1_eventlog.o tpm2_eventlog.o > tpm-$(CONFIG_ACPI) += tpm_ppi.o tpm_acpi.o > tpm-$(CONFIG_OF) += tpm_of.o > obj-$(CONFIG_TCG_TIS_CORE) += tpm_tis_core.o > diff --git a/drivers/char/tpm/tpm_eventlog.c b/drivers/char/tpm/tpm1_eventlog.c > similarity index 95% > rename from drivers/char/tpm/tpm_eventlog.c > rename to drivers/char/tpm/tpm1_eventlog.c > index 11bb113..9a8605e 100644 > --- a/drivers/char/tpm/tpm_eventlog.c > +++ b/drivers/char/tpm/tpm1_eventlog.c > @@ -390,9 +390,6 @@ int tpm_bios_log_setup(struct tpm_chip *chip) > unsigned int cnt; > int rc = 0; > > - if (chip->flags & TPM_CHIP_FLAG_TPM2) > - return 0; > - > rc = tpm_read_log(chip); > if (rc) > return rc; > @@ -407,7 +404,13 @@ int tpm_bios_log_setup(struct tpm_chip *chip) > cnt++; > > chip->bin_log_seqops.chip = chip; > - chip->bin_log_seqops.seqops = &tpm_binary_b_measurements_seqops; > + if (chip->flags & TPM_CHIP_FLAG_TPM2) > + chip->bin_log_seqops.seqops = > + &tpm2_binary_b_measurements_seqops; > + else > + chip->bin_log_seqops.seqops = > + &tpm_binary_b_measurements_seqops; > + > > chip->bios_dir[cnt] = > securityfs_create_file("binary_bios_measurements", > @@ -418,17 +421,21 @@ int tpm_bios_log_setup(struct tpm_chip *chip) > goto err; > cnt++; > > - chip->ascii_log_seqops.chip = chip; > - chip->ascii_log_seqops.seqops = &tpm_ascii_b_measurements_seqops; > + if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) { > > - chip->bios_dir[cnt] = > - securityfs_create_file("ascii_bios_measurements", > - 0440, chip->bios_dir[0], > - (void *)&chip->ascii_log_seqops, > - &tpm_bios_measurements_ops); > - if (IS_ERR(chip->bios_dir[cnt])) > - goto err; > - cnt++; > + chip->ascii_log_seqops.chip = chip; > + chip->ascii_log_seqops.seqops = > + &tpm_ascii_b_measurements_seqops; > + > + chip->bios_dir[cnt] = > + securityfs_create_file("ascii_bios_measurements", > + 0440, chip->bios_dir[0], > + (void *)&chip->ascii_log_seqops, > + &tpm_bios_measurements_ops); > + if (IS_ERR(chip->bios_dir[cnt])) > + goto err; > + cnt++; > + } > > return 0; > > diff --git a/drivers/char/tpm/tpm2_eventlog.c b/drivers/char/tpm/tpm2_eventlog.c > new file mode 100644 > index 0000000..63690d3 > --- /dev/null > +++ b/drivers/char/tpm/tpm2_eventlog.c > @@ -0,0 +1,203 @@ > +/* > + * Copyright (C) 2016 IBM Corporation > + * > + * Authors: > + * Nayna Jain <nayna@linux.vnet.ibm.com> > + * > + * Access to TPM 2.0 event log as written by Firmware. > + * It assumes that writer of event log has followed TCG Specification > + * for Family "2.0" and written the event data in little endian. > + * With that, it doesn't need any endian conversion for structure > + * content. > + * > + * This program is free software; you can redistribute it and/or > + * modify it under the terms of the GNU General Public License > + * as published by the Free Software Foundation; either version > + * 2 of the License, or (at your option) any later version. > + */ > + > +#include <linux/seq_file.h> > +#include <linux/fs.h> > +#include <linux/security.h> > +#include <linux/module.h> > +#include <linux/slab.h> > + > +#include "tpm.h" > +#include "tpm_eventlog.h" > + > +static int calc_tpm2_event_size(struct tcg_pcr_event2 *event, > + struct tcg_pcr_event *event_header) Bad alignment. > +{ > + struct tcg_efi_specid_event *efispecid; > + struct tcg_event_field *event_field; > + void *marker; > + void *marker_start; > + int i; > + int j; > + u16 halg; > + u32 halg_size; > + size_t size; > + > + /* > + * TPM 2.0 supports extend to multiple PCR Banks. This implies > + * event log also has multiple digest values, one for each PCR Bank. > + * This is called Crypto Agile Log Entry Format. > + * Below code implements the procedure defined in TCG EFI Protocol > + * Specification Family "2.0" to parse the event log in Crypto Agile > + * Log Entry Format. > + */ Please, document the function and remove this inline comment. > + > + marker = event; > + marker_start = marker; > + marker = marker + sizeof(event->pcr_idx) + sizeof(event->event_type) > + + sizeof(event->digests.count); > + > + efispecid = (struct tcg_efi_specid_event *) event_header->event; > + > + for (i = 0; (i < event->digests.count) && (i < TPM2_ACTIVE_PCR_BANKS); > + i++) { > + halg_size = sizeof(event->digests.digests[i].alg_id); > + memcpy(&halg, marker, halg_size); > + marker = marker + halg_size; > + for (j = 0; (j < efispecid->num_algs); j++) { > + if (halg == efispecid->digest_sizes[j].alg_id) { > + marker = marker + > + efispecid->digest_sizes[j].digest_size; > + break; > + } > + } > + } > + > + event_field = (struct tcg_event_field *) marker; > + marker = marker + sizeof(event_field->event_size) > + + event_field->event_size; > + size = marker - marker_start; > + > + if ((event->event_type == 0) && (event_field->event_size == 0)) > + return 0; > + > + return size; > +} > + > +static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos) > +{ > + struct tpm_chip *chip = m->private; > + struct tpm_bios_log *log = &chip->log; > + void *addr = log->bios_event_log; > + void *limit = log->bios_event_log_end; > + struct tcg_pcr_event *event_header; > + struct tcg_pcr_event2 *event; > + int i; > + size_t size; > + > + event_header = addr; > + size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event) > + + event_header->event_size; > + > + if (*pos == 0) { > + if (addr + size < limit) { > + if ((event_header->event_type == 0) && > + (event_header->event_size == 0)) > + return NULL; > + return SEQ_START_TOKEN; > + } > + } > + > + if (*pos > 0) { > + addr += size; > + event = addr; > + size = calc_tpm2_event_size(event, event_header); > + if ((addr + size >= limit) || (size == 0)) > + return NULL; > + } > + > + for (i = 0; i < (*pos - 1); i++) { > + event = addr; > + size = calc_tpm2_event_size(event, event_header); > + > + if ((addr + size >= limit) || (size == 0)) > + return NULL; > + addr += size; > + } > + > + return addr; > +} > + > +static void *tpm2_bios_measurements_next(struct seq_file *m, void *v, > + loff_t *pos) > +{ > + struct tcg_pcr_event *event_header; > + struct tcg_pcr_event2 *event; > + struct tpm_chip *chip = m->private; > + struct tpm_bios_log *log = &chip->log; > + void *limit = log->bios_event_log_end; > + void *marker; > + size_t event_size; > + > + event_header = log->bios_event_log; > + > + if (v == SEQ_START_TOKEN) { > + event_size = sizeof(struct tcg_pcr_event) > + - sizeof(event_header->event) > + + event_header->event_size; Bad alignment. Please, check the whole commit and if there is more of these.. > + marker = event_header; > + } else { > + event = v; > + event_size = calc_tpm2_event_size(event, event_header); > + if (event_size == 0) > + return NULL; > + marker = event; > + } > + > + marker = marker + event_size; > + if (marker >= limit) > + return NULL; > + v = marker; > + event = v; > + > + event_size = calc_tpm2_event_size(event, event_header); > + if (((v + event_size) >= limit) || (event_size == 0)) > + return NULL; > + > + (*pos)++; > + return v; > +} > + > +static void tpm2_bios_measurements_stop(struct seq_file *m, void *v) > +{ > +} > + > +static int tpm2_binary_bios_measurements_show(struct seq_file *m, void *v) > +{ > + struct tpm_chip *chip = m->private; > + struct tpm_bios_log *log = &chip->log; > + struct tcg_pcr_event *event_header = log->bios_event_log; > + struct tcg_pcr_event2 *event = v; > + void *temp_ptr; > + size_t size; > + > + if (v == SEQ_START_TOKEN) { > + size = sizeof(struct tcg_pcr_event) > + - sizeof(event_header->event) > + + event_header->event_size; > + > + temp_ptr = event_header; > + > + if (size > 0) > + seq_write(m, temp_ptr, size); > + } else { > + size = calc_tpm2_event_size(event, event_header); > + temp_ptr = event; > + if (size > 0) > + seq_write(m, temp_ptr, size); > + } > + > + return 0; > +} > + > +const struct seq_operations tpm2_binary_b_measurements_seqops = { > + .start = tpm2_bios_measurements_start, > + .next = tpm2_bios_measurements_next, > + .stop = tpm2_bios_measurements_stop, > + .show = tpm2_binary_bios_measurements_show, > +}; > diff --git a/drivers/char/tpm/tpm_eventlog.h b/drivers/char/tpm/tpm_eventlog.h > index 1660d74..6886a11 100644 > --- a/drivers/char/tpm/tpm_eventlog.h > +++ b/drivers/char/tpm/tpm_eventlog.h > @@ -2,9 +2,12 @@ > #ifndef __TPM_EVENTLOG_H__ > #define __TPM_EVENTLOG_H__ > > +#include <crypto/hash_info.h> > + > #define TCG_EVENT_NAME_LEN_MAX 255 > #define MAX_TEXT_EVENT 1000 /* Max event string length */ > #define ACPI_TCPA_SIG "TCPA" /* 0x41504354 /'TCPA' */ > +#define TPM2_ACTIVE_PCR_BANKS 3 > > #ifdef CONFIG_PPC64 > #define do_endian_conversion(x) be32_to_cpu(x) > @@ -73,6 +76,73 @@ enum tcpa_pc_event_ids { > HOST_TABLE_OF_DEVICES, > }; > > +/* > + * All the structures related to TPM 2.0 Event Log are taken from TCG EFI > + * Protocol Specification, Family "2.0". Document is available on link > + * http://www.trustedcomputinggroup.org/tcg-efi-protocol-specification/ . > + * Information is also available on TCG PC Client Platform Firmware Profile > + * Specification, Family "2.0". > + * Detailed digest structures for TPM 2.0 are defined in document > + * Trusted Platform Module Library Part 2: Structures, Family "2.0". > + */ > + > +/* TPM 2.0 Event log header algorithm spec. */ > +struct tcg_efi_specid_event_algs { > + u16 alg_id; > + u16 digest_size; > +} __packed; > + > +/* TPM 2.0 Event log header data. */ > +struct tcg_efi_specid_event { > + u8 signature[16]; > + u32 platform_class; > + u8 spec_version_minor; > + u8 spec_version_major; > + u8 spec_errata; > + u8 uintnsize; > + u32 num_algs; > + struct tcg_efi_specid_event_algs digest_sizes[TPM2_ACTIVE_PCR_BANKS]; > + u8 vendor_info_size; > + u8 vendor_info[0]; > +} __packed; > + > +/* TPM 2.0 Event Log Header. */ > +struct tcg_pcr_event { > + u32 pcr_idx; > + u32 event_type; > + u8 digest[20]; > + u32 event_size; > + u8 event[0]; > +} __packed; > + > +/* TPM 2.0 Crypto agile algorithm and respective digest. */ > +struct tpmt_ha { > + u16 alg_id; > + u8 digest[SHA384_DIGEST_SIZE]; > +} __packed; > + > +/* TPM 2.0 Crypto agile digests list. */ > +struct tpml_digest_values { > + u32 count; > + struct tpmt_ha digests[TPM2_ACTIVE_PCR_BANKS]; > +} __packed; > + > +/* TPM 2.0 Event field structure. */ > +struct tcg_event_field { > + u32 event_size; > + u8 event[0]; > +} __packed; > + > +/* TPM 2.0 Crypto agile log entry format. */ These one line comments are next to useless. Please remove them. > +struct tcg_pcr_event2 { > + u32 pcr_idx; > + u32 event_type; > + struct tpml_digest_values digests; > + 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 > -- > 2.5.0 > /Jarkko -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/03/2017 03:42 AM, Jarkko Sakkinen wrote: > On Sun, Dec 11, 2016 at 12:35:33AM -0500, Nayna Jain wrote: >> Unlike the device driver support for TPM 1.2, the TPM 2.0 does >> not support the securityfs pseudo files for displaying the >> firmware event log. >> >> This patch enables support for providing the TPM 2.0 event log in >> binary form. TPM 2.0 event log supports a crypto agile format that >> records multiple digests, which is different from TPM 1.2. This >> patch enables the tpm_bios_log_setup for TPM 2.0 and adds the >> event log parser which understand the TPM 2.0 crypto agile format. >> >> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> > > There is something fundamentally wrong in this commit. > > You must not allow this feature unless CONFIG_OF is set. It is the only > interface where the supply path of the event log is well defined on > platforms that include a TPM 2.0 chip. As per current implementation, if ACPI with TPM 2.0 doesn't support event log, tpm_read_log_acpi() is expected to return rc and tpm_bios_log_setup will not create securityfs. This is inline with our design for TPM 1.2 event log. > > There's buch casts in the form '(char *) foo'. They should be > '(char *)foo'. Will fix these and other comments. Thanks & Regards, - Nayna > >> --- >> drivers/char/tpm/Makefile | 2 +- >> .../char/tpm/{tpm_eventlog.c => tpm1_eventlog.c} | 35 ++-- >> drivers/char/tpm/tpm2_eventlog.c | 203 +++++++++++++++++++++ >> drivers/char/tpm/tpm_eventlog.h | 70 +++++++ >> 4 files changed, 295 insertions(+), 15 deletions(-) >> rename drivers/char/tpm/{tpm_eventlog.c => tpm1_eventlog.c} (95%) >> create mode 100644 drivers/char/tpm/tpm2_eventlog.c >> >> diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile >> index a05b1eb..3d386a8 100644 >> --- a/drivers/char/tpm/Makefile >> +++ b/drivers/char/tpm/Makefile >> @@ -3,7 +3,7 @@ >> # >> obj-$(CONFIG_TCG_TPM) += tpm.o >> tpm-y := tpm-interface.o tpm-dev.o tpm-sysfs.o tpm-chip.o tpm2-cmd.o \ >> - tpm_eventlog.o >> + tpm1_eventlog.o tpm2_eventlog.o >> tpm-$(CONFIG_ACPI) += tpm_ppi.o tpm_acpi.o >> tpm-$(CONFIG_OF) += tpm_of.o >> obj-$(CONFIG_TCG_TIS_CORE) += tpm_tis_core.o >> diff --git a/drivers/char/tpm/tpm_eventlog.c b/drivers/char/tpm/tpm1_eventlog.c >> similarity index 95% >> rename from drivers/char/tpm/tpm_eventlog.c >> rename to drivers/char/tpm/tpm1_eventlog.c >> index 11bb113..9a8605e 100644 >> --- a/drivers/char/tpm/tpm_eventlog.c >> +++ b/drivers/char/tpm/tpm1_eventlog.c >> @@ -390,9 +390,6 @@ int tpm_bios_log_setup(struct tpm_chip *chip) >> unsigned int cnt; >> int rc = 0; >> >> - if (chip->flags & TPM_CHIP_FLAG_TPM2) >> - return 0; >> - >> rc = tpm_read_log(chip); >> if (rc) >> return rc; >> @@ -407,7 +404,13 @@ int tpm_bios_log_setup(struct tpm_chip *chip) >> cnt++; >> >> chip->bin_log_seqops.chip = chip; >> - chip->bin_log_seqops.seqops = &tpm_binary_b_measurements_seqops; >> + if (chip->flags & TPM_CHIP_FLAG_TPM2) >> + chip->bin_log_seqops.seqops = >> + &tpm2_binary_b_measurements_seqops; >> + else >> + chip->bin_log_seqops.seqops = >> + &tpm_binary_b_measurements_seqops; >> + >> >> chip->bios_dir[cnt] = >> securityfs_create_file("binary_bios_measurements", >> @@ -418,17 +421,21 @@ int tpm_bios_log_setup(struct tpm_chip *chip) >> goto err; >> cnt++; >> >> - chip->ascii_log_seqops.chip = chip; >> - chip->ascii_log_seqops.seqops = &tpm_ascii_b_measurements_seqops; >> + if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) { >> >> - chip->bios_dir[cnt] = >> - securityfs_create_file("ascii_bios_measurements", >> - 0440, chip->bios_dir[0], >> - (void *)&chip->ascii_log_seqops, >> - &tpm_bios_measurements_ops); >> - if (IS_ERR(chip->bios_dir[cnt])) >> - goto err; >> - cnt++; >> + chip->ascii_log_seqops.chip = chip; >> + chip->ascii_log_seqops.seqops = >> + &tpm_ascii_b_measurements_seqops; >> + >> + chip->bios_dir[cnt] = >> + securityfs_create_file("ascii_bios_measurements", >> + 0440, chip->bios_dir[0], >> + (void *)&chip->ascii_log_seqops, >> + &tpm_bios_measurements_ops); >> + if (IS_ERR(chip->bios_dir[cnt])) >> + goto err; >> + cnt++; >> + } >> >> return 0; >> >> diff --git a/drivers/char/tpm/tpm2_eventlog.c b/drivers/char/tpm/tpm2_eventlog.c >> new file mode 100644 >> index 0000000..63690d3 >> --- /dev/null >> +++ b/drivers/char/tpm/tpm2_eventlog.c >> @@ -0,0 +1,203 @@ >> +/* >> + * Copyright (C) 2016 IBM Corporation >> + * >> + * Authors: >> + * Nayna Jain <nayna@linux.vnet.ibm.com> >> + * >> + * Access to TPM 2.0 event log as written by Firmware. >> + * It assumes that writer of event log has followed TCG Specification >> + * for Family "2.0" and written the event data in little endian. >> + * With that, it doesn't need any endian conversion for structure >> + * content. >> + * >> + * This program is free software; you can redistribute it and/or >> + * modify it under the terms of the GNU General Public License >> + * as published by the Free Software Foundation; either version >> + * 2 of the License, or (at your option) any later version. >> + */ >> + >> +#include <linux/seq_file.h> >> +#include <linux/fs.h> >> +#include <linux/security.h> >> +#include <linux/module.h> >> +#include <linux/slab.h> >> + >> +#include "tpm.h" >> +#include "tpm_eventlog.h" >> + >> +static int calc_tpm2_event_size(struct tcg_pcr_event2 *event, >> + struct tcg_pcr_event *event_header) > > Bad alignment. > >> +{ >> + struct tcg_efi_specid_event *efispecid; >> + struct tcg_event_field *event_field; >> + void *marker; >> + void *marker_start; >> + int i; >> + int j; >> + u16 halg; >> + u32 halg_size; >> + size_t size; >> + >> + /* >> + * TPM 2.0 supports extend to multiple PCR Banks. This implies >> + * event log also has multiple digest values, one for each PCR Bank. >> + * This is called Crypto Agile Log Entry Format. >> + * Below code implements the procedure defined in TCG EFI Protocol >> + * Specification Family "2.0" to parse the event log in Crypto Agile >> + * Log Entry Format. >> + */ > > Please, document the function and remove this inline comment. > >> + >> + marker = event; >> + marker_start = marker; >> + marker = marker + sizeof(event->pcr_idx) + sizeof(event->event_type) >> + + sizeof(event->digests.count); >> + >> + efispecid = (struct tcg_efi_specid_event *) event_header->event; >> + >> + for (i = 0; (i < event->digests.count) && (i < TPM2_ACTIVE_PCR_BANKS); >> + i++) { >> + halg_size = sizeof(event->digests.digests[i].alg_id); >> + memcpy(&halg, marker, halg_size); >> + marker = marker + halg_size; >> + for (j = 0; (j < efispecid->num_algs); j++) { >> + if (halg == efispecid->digest_sizes[j].alg_id) { >> + marker = marker + >> + efispecid->digest_sizes[j].digest_size; >> + break; >> + } >> + } >> + } >> + >> + event_field = (struct tcg_event_field *) marker; >> + marker = marker + sizeof(event_field->event_size) >> + + event_field->event_size; >> + size = marker - marker_start; >> + >> + if ((event->event_type == 0) && (event_field->event_size == 0)) >> + return 0; >> + >> + return size; >> +} >> + >> +static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos) >> +{ >> + struct tpm_chip *chip = m->private; >> + struct tpm_bios_log *log = &chip->log; >> + void *addr = log->bios_event_log; >> + void *limit = log->bios_event_log_end; >> + struct tcg_pcr_event *event_header; >> + struct tcg_pcr_event2 *event; >> + int i; >> + size_t size; >> + >> + event_header = addr; >> + size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event) >> + + event_header->event_size; >> + >> + if (*pos == 0) { >> + if (addr + size < limit) { >> + if ((event_header->event_type == 0) && >> + (event_header->event_size == 0)) >> + return NULL; >> + return SEQ_START_TOKEN; >> + } >> + } >> + >> + if (*pos > 0) { >> + addr += size; >> + event = addr; >> + size = calc_tpm2_event_size(event, event_header); >> + if ((addr + size >= limit) || (size == 0)) >> + return NULL; >> + } >> + >> + for (i = 0; i < (*pos - 1); i++) { >> + event = addr; >> + size = calc_tpm2_event_size(event, event_header); >> + >> + if ((addr + size >= limit) || (size == 0)) >> + return NULL; >> + addr += size; >> + } >> + >> + return addr; >> +} >> + >> +static void *tpm2_bios_measurements_next(struct seq_file *m, void *v, >> + loff_t *pos) >> +{ >> + struct tcg_pcr_event *event_header; >> + struct tcg_pcr_event2 *event; >> + struct tpm_chip *chip = m->private; >> + struct tpm_bios_log *log = &chip->log; >> + void *limit = log->bios_event_log_end; >> + void *marker; >> + size_t event_size; >> + >> + event_header = log->bios_event_log; >> + >> + if (v == SEQ_START_TOKEN) { >> + event_size = sizeof(struct tcg_pcr_event) >> + - sizeof(event_header->event) >> + + event_header->event_size; > > Bad alignment. Please, check the whole commit and if there is more of > these.. > >> + marker = event_header; >> + } else { >> + event = v; >> + event_size = calc_tpm2_event_size(event, event_header); >> + if (event_size == 0) >> + return NULL; >> + marker = event; >> + } >> + >> + marker = marker + event_size; >> + if (marker >= limit) >> + return NULL; >> + v = marker; >> + event = v; >> + >> + event_size = calc_tpm2_event_size(event, event_header); >> + if (((v + event_size) >= limit) || (event_size == 0)) >> + return NULL; >> + >> + (*pos)++; >> + return v; >> +} >> + >> +static void tpm2_bios_measurements_stop(struct seq_file *m, void *v) >> +{ >> +} >> + >> +static int tpm2_binary_bios_measurements_show(struct seq_file *m, void *v) >> +{ >> + struct tpm_chip *chip = m->private; >> + struct tpm_bios_log *log = &chip->log; >> + struct tcg_pcr_event *event_header = log->bios_event_log; >> + struct tcg_pcr_event2 *event = v; >> + void *temp_ptr; >> + size_t size; >> + >> + if (v == SEQ_START_TOKEN) { >> + size = sizeof(struct tcg_pcr_event) >> + - sizeof(event_header->event) >> + + event_header->event_size; >> + >> + temp_ptr = event_header; >> + >> + if (size > 0) >> + seq_write(m, temp_ptr, size); >> + } else { >> + size = calc_tpm2_event_size(event, event_header); >> + temp_ptr = event; >> + if (size > 0) >> + seq_write(m, temp_ptr, size); >> + } >> + >> + return 0; >> +} >> + >> +const struct seq_operations tpm2_binary_b_measurements_seqops = { >> + .start = tpm2_bios_measurements_start, >> + .next = tpm2_bios_measurements_next, >> + .stop = tpm2_bios_measurements_stop, >> + .show = tpm2_binary_bios_measurements_show, >> +}; >> diff --git a/drivers/char/tpm/tpm_eventlog.h b/drivers/char/tpm/tpm_eventlog.h >> index 1660d74..6886a11 100644 >> --- a/drivers/char/tpm/tpm_eventlog.h >> +++ b/drivers/char/tpm/tpm_eventlog.h >> @@ -2,9 +2,12 @@ >> #ifndef __TPM_EVENTLOG_H__ >> #define __TPM_EVENTLOG_H__ >> >> +#include <crypto/hash_info.h> >> + >> #define TCG_EVENT_NAME_LEN_MAX 255 >> #define MAX_TEXT_EVENT 1000 /* Max event string length */ >> #define ACPI_TCPA_SIG "TCPA" /* 0x41504354 /'TCPA' */ >> +#define TPM2_ACTIVE_PCR_BANKS 3 >> >> #ifdef CONFIG_PPC64 >> #define do_endian_conversion(x) be32_to_cpu(x) >> @@ -73,6 +76,73 @@ enum tcpa_pc_event_ids { >> HOST_TABLE_OF_DEVICES, >> }; >> >> +/* >> + * All the structures related to TPM 2.0 Event Log are taken from TCG EFI >> + * Protocol Specification, Family "2.0". Document is available on link >> + * http://www.trustedcomputinggroup.org/tcg-efi-protocol-specification/ . >> + * Information is also available on TCG PC Client Platform Firmware Profile >> + * Specification, Family "2.0". >> + * Detailed digest structures for TPM 2.0 are defined in document >> + * Trusted Platform Module Library Part 2: Structures, Family "2.0". >> + */ >> + >> +/* TPM 2.0 Event log header algorithm spec. */ >> +struct tcg_efi_specid_event_algs { >> + u16 alg_id; >> + u16 digest_size; >> +} __packed; >> + >> +/* TPM 2.0 Event log header data. */ >> +struct tcg_efi_specid_event { >> + u8 signature[16]; >> + u32 platform_class; >> + u8 spec_version_minor; >> + u8 spec_version_major; >> + u8 spec_errata; >> + u8 uintnsize; >> + u32 num_algs; >> + struct tcg_efi_specid_event_algs digest_sizes[TPM2_ACTIVE_PCR_BANKS]; >> + u8 vendor_info_size; >> + u8 vendor_info[0]; >> +} __packed; >> + >> +/* TPM 2.0 Event Log Header. */ >> +struct tcg_pcr_event { >> + u32 pcr_idx; >> + u32 event_type; >> + u8 digest[20]; >> + u32 event_size; >> + u8 event[0]; >> +} __packed; >> + >> +/* TPM 2.0 Crypto agile algorithm and respective digest. */ >> +struct tpmt_ha { >> + u16 alg_id; >> + u8 digest[SHA384_DIGEST_SIZE]; >> +} __packed; >> + >> +/* TPM 2.0 Crypto agile digests list. */ >> +struct tpml_digest_values { >> + u32 count; >> + struct tpmt_ha digests[TPM2_ACTIVE_PCR_BANKS]; >> +} __packed; >> + >> +/* TPM 2.0 Event field structure. */ >> +struct tcg_event_field { >> + u32 event_size; >> + u8 event[0]; >> +} __packed; >> + >> +/* TPM 2.0 Crypto agile log entry format. */ > > These one line comments are next to useless. Please remove them. > >> +struct tcg_pcr_event2 { >> + u32 pcr_idx; >> + u32 event_type; >> + struct tpml_digest_values digests; >> + 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 >> -- >> 2.5.0 >> > > /Jarkko > -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Jan 03, 2017 at 01:09:18PM +0530, Nayna wrote: > > > On 01/03/2017 03:42 AM, Jarkko Sakkinen wrote: > > On Sun, Dec 11, 2016 at 12:35:33AM -0500, Nayna Jain wrote: > > > Unlike the device driver support for TPM 1.2, the TPM 2.0 does > > > not support the securityfs pseudo files for displaying the > > > firmware event log. > > > > > > This patch enables support for providing the TPM 2.0 event log in > > > binary form. TPM 2.0 event log supports a crypto agile format that > > > records multiple digests, which is different from TPM 1.2. This > > > patch enables the tpm_bios_log_setup for TPM 2.0 and adds the > > > event log parser which understand the TPM 2.0 crypto agile format. > > > > > > Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> > > > > There is something fundamentally wrong in this commit. > > > > You must not allow this feature unless CONFIG_OF is set. It is the only > > interface where the supply path of the event log is well defined on > > platforms that include a TPM 2.0 chip. > > As per current implementation, if ACPI with TPM 2.0 doesn't support event > log, tpm_read_log_acpi() is expected to return rc and tpm_bios_log_setup > will not create securityfs. This is inline with our design for TPM 1.2 event > log. At minimum you must have a check for TPM_CHIP_FLAG_TPM2 in the beginning of tpm_read_log_acpi. It is wrong to even try to open TCPA in this case. /Jarkko -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/03/2017 07:03 PM, Jarkko Sakkinen wrote: > On Tue, Jan 03, 2017 at 01:09:18PM +0530, Nayna wrote: >> >> >> On 01/03/2017 03:42 AM, Jarkko Sakkinen wrote: >>> On Sun, Dec 11, 2016 at 12:35:33AM -0500, Nayna Jain wrote: >>>> Unlike the device driver support for TPM 1.2, the TPM 2.0 does >>>> not support the securityfs pseudo files for displaying the >>>> firmware event log. >>>> >>>> This patch enables support for providing the TPM 2.0 event log in >>>> binary form. TPM 2.0 event log supports a crypto agile format that >>>> records multiple digests, which is different from TPM 1.2. This >>>> patch enables the tpm_bios_log_setup for TPM 2.0 and adds the >>>> event log parser which understand the TPM 2.0 crypto agile format. >>>> >>>> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> >>> >>> There is something fundamentally wrong in this commit. >>> >>> You must not allow this feature unless CONFIG_OF is set. It is the only >>> interface where the supply path of the event log is well defined on >>> platforms that include a TPM 2.0 chip. >> >> As per current implementation, if ACPI with TPM 2.0 doesn't support event >> log, tpm_read_log_acpi() is expected to return rc and tpm_bios_log_setup >> will not create securityfs. This is inline with our design for TPM 1.2 event >> log. > > At minimum you must have a check for TPM_CHIP_FLAG_TPM2 in the beginning > of tpm_read_log_acpi. It is wrong to even try to open TCPA in this case. Sure, will add this check and return -ENODEV if check passes. Thanks & Regards, - Nayna > > /Jarkko > -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Jan 04, 2017 at 02:08:06PM +0530, Nayna wrote: > > > On 01/03/2017 07:03 PM, Jarkko Sakkinen wrote: > > On Tue, Jan 03, 2017 at 01:09:18PM +0530, Nayna wrote: > > > > > > > > > On 01/03/2017 03:42 AM, Jarkko Sakkinen wrote: > > > > On Sun, Dec 11, 2016 at 12:35:33AM -0500, Nayna Jain wrote: > > > > > Unlike the device driver support for TPM 1.2, the TPM 2.0 does > > > > > not support the securityfs pseudo files for displaying the > > > > > firmware event log. > > > > > > > > > > This patch enables support for providing the TPM 2.0 event log in > > > > > binary form. TPM 2.0 event log supports a crypto agile format that > > > > > records multiple digests, which is different from TPM 1.2. This > > > > > patch enables the tpm_bios_log_setup for TPM 2.0 and adds the > > > > > event log parser which understand the TPM 2.0 crypto agile format. > > > > > > > > > > Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> > > > > > > > > There is something fundamentally wrong in this commit. > > > > > > > > You must not allow this feature unless CONFIG_OF is set. It is the only > > > > interface where the supply path of the event log is well defined on > > > > platforms that include a TPM 2.0 chip. > > > > > > As per current implementation, if ACPI with TPM 2.0 doesn't support event > > > log, tpm_read_log_acpi() is expected to return rc and tpm_bios_log_setup > > > will not create securityfs. This is inline with our design for TPM 1.2 event > > > log. > > > > At minimum you must have a check for TPM_CHIP_FLAG_TPM2 in the beginning > > of tpm_read_log_acpi. It is wrong to even try to open TCPA in this case. > > Sure, will add this check and return -ENODEV if check passes. Yeah, this is acceptable for me. > Thanks & Regards, > - Nayna /Jarkko -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile index a05b1eb..3d386a8 100644 --- a/drivers/char/tpm/Makefile +++ b/drivers/char/tpm/Makefile @@ -3,7 +3,7 @@ # obj-$(CONFIG_TCG_TPM) += tpm.o tpm-y := tpm-interface.o tpm-dev.o tpm-sysfs.o tpm-chip.o tpm2-cmd.o \ - tpm_eventlog.o + tpm1_eventlog.o tpm2_eventlog.o tpm-$(CONFIG_ACPI) += tpm_ppi.o tpm_acpi.o tpm-$(CONFIG_OF) += tpm_of.o obj-$(CONFIG_TCG_TIS_CORE) += tpm_tis_core.o diff --git a/drivers/char/tpm/tpm_eventlog.c b/drivers/char/tpm/tpm1_eventlog.c similarity index 95% rename from drivers/char/tpm/tpm_eventlog.c rename to drivers/char/tpm/tpm1_eventlog.c index 11bb113..9a8605e 100644 --- a/drivers/char/tpm/tpm_eventlog.c +++ b/drivers/char/tpm/tpm1_eventlog.c @@ -390,9 +390,6 @@ int tpm_bios_log_setup(struct tpm_chip *chip) unsigned int cnt; int rc = 0; - if (chip->flags & TPM_CHIP_FLAG_TPM2) - return 0; - rc = tpm_read_log(chip); if (rc) return rc; @@ -407,7 +404,13 @@ int tpm_bios_log_setup(struct tpm_chip *chip) cnt++; chip->bin_log_seqops.chip = chip; - chip->bin_log_seqops.seqops = &tpm_binary_b_measurements_seqops; + if (chip->flags & TPM_CHIP_FLAG_TPM2) + chip->bin_log_seqops.seqops = + &tpm2_binary_b_measurements_seqops; + else + chip->bin_log_seqops.seqops = + &tpm_binary_b_measurements_seqops; + chip->bios_dir[cnt] = securityfs_create_file("binary_bios_measurements", @@ -418,17 +421,21 @@ int tpm_bios_log_setup(struct tpm_chip *chip) goto err; cnt++; - chip->ascii_log_seqops.chip = chip; - chip->ascii_log_seqops.seqops = &tpm_ascii_b_measurements_seqops; + if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) { - chip->bios_dir[cnt] = - securityfs_create_file("ascii_bios_measurements", - 0440, chip->bios_dir[0], - (void *)&chip->ascii_log_seqops, - &tpm_bios_measurements_ops); - if (IS_ERR(chip->bios_dir[cnt])) - goto err; - cnt++; + chip->ascii_log_seqops.chip = chip; + chip->ascii_log_seqops.seqops = + &tpm_ascii_b_measurements_seqops; + + chip->bios_dir[cnt] = + securityfs_create_file("ascii_bios_measurements", + 0440, chip->bios_dir[0], + (void *)&chip->ascii_log_seqops, + &tpm_bios_measurements_ops); + if (IS_ERR(chip->bios_dir[cnt])) + goto err; + cnt++; + } return 0; diff --git a/drivers/char/tpm/tpm2_eventlog.c b/drivers/char/tpm/tpm2_eventlog.c new file mode 100644 index 0000000..63690d3 --- /dev/null +++ b/drivers/char/tpm/tpm2_eventlog.c @@ -0,0 +1,203 @@ +/* + * Copyright (C) 2016 IBM Corporation + * + * Authors: + * Nayna Jain <nayna@linux.vnet.ibm.com> + * + * Access to TPM 2.0 event log as written by Firmware. + * It assumes that writer of event log has followed TCG Specification + * for Family "2.0" and written the event data in little endian. + * With that, it doesn't need any endian conversion for structure + * content. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + */ + +#include <linux/seq_file.h> +#include <linux/fs.h> +#include <linux/security.h> +#include <linux/module.h> +#include <linux/slab.h> + +#include "tpm.h" +#include "tpm_eventlog.h" + +static int calc_tpm2_event_size(struct tcg_pcr_event2 *event, + struct tcg_pcr_event *event_header) +{ + struct tcg_efi_specid_event *efispecid; + struct tcg_event_field *event_field; + void *marker; + void *marker_start; + int i; + int j; + u16 halg; + u32 halg_size; + size_t size; + + /* + * TPM 2.0 supports extend to multiple PCR Banks. This implies + * event log also has multiple digest values, one for each PCR Bank. + * This is called Crypto Agile Log Entry Format. + * Below code implements the procedure defined in TCG EFI Protocol + * Specification Family "2.0" to parse the event log in Crypto Agile + * Log Entry Format. + */ + + marker = event; + marker_start = marker; + marker = marker + sizeof(event->pcr_idx) + sizeof(event->event_type) + + sizeof(event->digests.count); + + efispecid = (struct tcg_efi_specid_event *) event_header->event; + + for (i = 0; (i < event->digests.count) && (i < TPM2_ACTIVE_PCR_BANKS); + i++) { + halg_size = sizeof(event->digests.digests[i].alg_id); + memcpy(&halg, marker, halg_size); + marker = marker + halg_size; + for (j = 0; (j < efispecid->num_algs); j++) { + if (halg == efispecid->digest_sizes[j].alg_id) { + marker = marker + + efispecid->digest_sizes[j].digest_size; + break; + } + } + } + + event_field = (struct tcg_event_field *) marker; + marker = marker + sizeof(event_field->event_size) + + event_field->event_size; + size = marker - marker_start; + + if ((event->event_type == 0) && (event_field->event_size == 0)) + return 0; + + return size; +} + +static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos) +{ + struct tpm_chip *chip = m->private; + struct tpm_bios_log *log = &chip->log; + void *addr = log->bios_event_log; + void *limit = log->bios_event_log_end; + struct tcg_pcr_event *event_header; + struct tcg_pcr_event2 *event; + int i; + size_t size; + + event_header = addr; + size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event) + + event_header->event_size; + + if (*pos == 0) { + if (addr + size < limit) { + if ((event_header->event_type == 0) && + (event_header->event_size == 0)) + return NULL; + return SEQ_START_TOKEN; + } + } + + if (*pos > 0) { + addr += size; + event = addr; + size = calc_tpm2_event_size(event, event_header); + if ((addr + size >= limit) || (size == 0)) + return NULL; + } + + for (i = 0; i < (*pos - 1); i++) { + event = addr; + size = calc_tpm2_event_size(event, event_header); + + if ((addr + size >= limit) || (size == 0)) + return NULL; + addr += size; + } + + return addr; +} + +static void *tpm2_bios_measurements_next(struct seq_file *m, void *v, + loff_t *pos) +{ + struct tcg_pcr_event *event_header; + struct tcg_pcr_event2 *event; + struct tpm_chip *chip = m->private; + struct tpm_bios_log *log = &chip->log; + void *limit = log->bios_event_log_end; + void *marker; + size_t event_size; + + event_header = log->bios_event_log; + + if (v == SEQ_START_TOKEN) { + event_size = sizeof(struct tcg_pcr_event) + - sizeof(event_header->event) + + event_header->event_size; + marker = event_header; + } else { + event = v; + event_size = calc_tpm2_event_size(event, event_header); + if (event_size == 0) + return NULL; + marker = event; + } + + marker = marker + event_size; + if (marker >= limit) + return NULL; + v = marker; + event = v; + + event_size = calc_tpm2_event_size(event, event_header); + if (((v + event_size) >= limit) || (event_size == 0)) + return NULL; + + (*pos)++; + return v; +} + +static void tpm2_bios_measurements_stop(struct seq_file *m, void *v) +{ +} + +static int tpm2_binary_bios_measurements_show(struct seq_file *m, void *v) +{ + struct tpm_chip *chip = m->private; + struct tpm_bios_log *log = &chip->log; + struct tcg_pcr_event *event_header = log->bios_event_log; + struct tcg_pcr_event2 *event = v; + void *temp_ptr; + size_t size; + + if (v == SEQ_START_TOKEN) { + size = sizeof(struct tcg_pcr_event) + - sizeof(event_header->event) + + event_header->event_size; + + temp_ptr = event_header; + + if (size > 0) + seq_write(m, temp_ptr, size); + } else { + size = calc_tpm2_event_size(event, event_header); + temp_ptr = event; + if (size > 0) + seq_write(m, temp_ptr, size); + } + + return 0; +} + +const struct seq_operations tpm2_binary_b_measurements_seqops = { + .start = tpm2_bios_measurements_start, + .next = tpm2_bios_measurements_next, + .stop = tpm2_bios_measurements_stop, + .show = tpm2_binary_bios_measurements_show, +}; diff --git a/drivers/char/tpm/tpm_eventlog.h b/drivers/char/tpm/tpm_eventlog.h index 1660d74..6886a11 100644 --- a/drivers/char/tpm/tpm_eventlog.h +++ b/drivers/char/tpm/tpm_eventlog.h @@ -2,9 +2,12 @@ #ifndef __TPM_EVENTLOG_H__ #define __TPM_EVENTLOG_H__ +#include <crypto/hash_info.h> + #define TCG_EVENT_NAME_LEN_MAX 255 #define MAX_TEXT_EVENT 1000 /* Max event string length */ #define ACPI_TCPA_SIG "TCPA" /* 0x41504354 /'TCPA' */ +#define TPM2_ACTIVE_PCR_BANKS 3 #ifdef CONFIG_PPC64 #define do_endian_conversion(x) be32_to_cpu(x) @@ -73,6 +76,73 @@ enum tcpa_pc_event_ids { HOST_TABLE_OF_DEVICES, }; +/* + * All the structures related to TPM 2.0 Event Log are taken from TCG EFI + * Protocol Specification, Family "2.0". Document is available on link + * http://www.trustedcomputinggroup.org/tcg-efi-protocol-specification/ . + * Information is also available on TCG PC Client Platform Firmware Profile + * Specification, Family "2.0". + * Detailed digest structures for TPM 2.0 are defined in document + * Trusted Platform Module Library Part 2: Structures, Family "2.0". + */ + +/* TPM 2.0 Event log header algorithm spec. */ +struct tcg_efi_specid_event_algs { + u16 alg_id; + u16 digest_size; +} __packed; + +/* TPM 2.0 Event log header data. */ +struct tcg_efi_specid_event { + u8 signature[16]; + u32 platform_class; + u8 spec_version_minor; + u8 spec_version_major; + u8 spec_errata; + u8 uintnsize; + u32 num_algs; + struct tcg_efi_specid_event_algs digest_sizes[TPM2_ACTIVE_PCR_BANKS]; + u8 vendor_info_size; + u8 vendor_info[0]; +} __packed; + +/* TPM 2.0 Event Log Header. */ +struct tcg_pcr_event { + u32 pcr_idx; + u32 event_type; + u8 digest[20]; + u32 event_size; + u8 event[0]; +} __packed; + +/* TPM 2.0 Crypto agile algorithm and respective digest. */ +struct tpmt_ha { + u16 alg_id; + u8 digest[SHA384_DIGEST_SIZE]; +} __packed; + +/* TPM 2.0 Crypto agile digests list. */ +struct tpml_digest_values { + u32 count; + struct tpmt_ha digests[TPM2_ACTIVE_PCR_BANKS]; +} __packed; + +/* TPM 2.0 Event field structure. */ +struct tcg_event_field { + u32 event_size; + u8 event[0]; +} __packed; + +/* TPM 2.0 Crypto agile log entry format. */ +struct tcg_pcr_event2 { + u32 pcr_idx; + u32 event_type; + struct tpml_digest_values digests; + 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
Unlike the device driver support for TPM 1.2, the TPM 2.0 does not support the securityfs pseudo files for displaying the firmware event log. This patch enables support for providing the TPM 2.0 event log in binary form. TPM 2.0 event log supports a crypto agile format that records multiple digests, which is different from TPM 1.2. This patch enables the tpm_bios_log_setup for TPM 2.0 and adds the event log parser which understand the TPM 2.0 crypto agile format. Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> --- drivers/char/tpm/Makefile | 2 +- .../char/tpm/{tpm_eventlog.c => tpm1_eventlog.c} | 35 ++-- drivers/char/tpm/tpm2_eventlog.c | 203 +++++++++++++++++++++ drivers/char/tpm/tpm_eventlog.h | 70 +++++++ 4 files changed, 295 insertions(+), 15 deletions(-) rename drivers/char/tpm/{tpm_eventlog.c => tpm1_eventlog.c} (95%) create mode 100644 drivers/char/tpm/tpm2_eventlog.c