Re: [PATCHC v7 02/10] ima: on soft reboot, restore the measurement list

[Dmitry Kasatkin]

On Thu, Nov 10, 2016 at 4:56 PM, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> The TPM PCRs are only reset on a hard reboot.  In order to validate a
> TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
> of the running kernel must be saved and restored on boot.  This patch
> restores the measurement list.
>
> Changelog v7:
> - add and fix missing buffer length checking (reported by D. Kasatkin)
> - clean up ima_restore_measurement_list() a bit
>
> Changelog v5:
> - replace CONFIG_KEXEC_FILE with architecture CONFIG_HAVE_IMA_KEXEC (Thiago)
> - replace kexec_get_handover_buffer() with ima_get_kexec_buffer() (Thiago)
> - replace kexec_free_handover_buffer() with ima_free_kexec_buffer() (Thiago)
> - remove unnecessary includes from ima_kexec.c (Thiago)
> - fix off-by-one error when checking hdr_v1->template_name_len (Colin King)
>
> Changelog v2:
> - redefined ima_kexec_hdr to use types with well defined sizes (M. Ellerman)
> - defined missing ima_load_kexec_buffer() stub function
>
> Changelog v1:
> - call ima_load_kexec_buffer() (Thiago)
>
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> ---
>  security/integrity/ima/Makefile       |   1 +
>  security/integrity/ima/ima.h          |  21 ++++
>  security/integrity/ima/ima_init.c     |   2 +
>  security/integrity/ima/ima_kexec.c    |  44 +++++++++
>  security/integrity/ima/ima_queue.c    |  10 ++
>  security/integrity/ima/ima_template.c | 177 ++++++++++++++++++++++++++++++++++
>  6 files changed, 255 insertions(+)
>  create mode 100644 security/integrity/ima/ima_kexec.c
>
> diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
> index 9aeaedad1e2b..29f198bde02b 100644
> --- a/security/integrity/ima/Makefile
> +++ b/security/integrity/ima/Makefile
> @@ -8,4 +8,5 @@ obj-$(CONFIG_IMA) += ima.o
>  ima-y := ima_fs.o ima_queue.o ima_init.o ima_main.o ima_crypto.o ima_api.o \
>          ima_policy.o ima_template.o ima_template_lib.o
>  ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
> +ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
>  obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index db25f54a04fe..51dc8d57d64d 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -28,6 +28,10 @@
>
>  #include "../integrity.h"
>
> +#ifdef CONFIG_HAVE_IMA_KEXEC
> +#include <asm/ima.h>
> +#endif
> +
>  enum ima_show_type { IMA_SHOW_BINARY, IMA_SHOW_BINARY_NO_FIELD_LEN,
>                      IMA_SHOW_BINARY_OLD_STRING_FMT, IMA_SHOW_ASCII };
>  enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8 };
> @@ -102,6 +106,21 @@ struct ima_queue_entry {
>  };
>  extern struct list_head ima_measurements;      /* list of all measurements */
>
> +/* Some details preceding the binary serialized measurement list */
> +struct ima_kexec_hdr {
> +       u16 version;
> +       u16 _reserved0;
> +       u32 _reserved1;
> +       u64 buffer_size;
> +       u64 count;
> +};
> +
> +#ifdef CONFIG_HAVE_IMA_KEXEC
> +void ima_load_kexec_buffer(void);
> +#else
> +static inline void ima_load_kexec_buffer(void) {}
> +#endif /* CONFIG_HAVE_IMA_KEXEC */
> +
>  /* Internal IMA function definitions */
>  int ima_init(void);
>  int ima_fs_init(void);
> @@ -122,6 +141,8 @@ int ima_init_crypto(void);
>  void ima_putc(struct seq_file *m, void *data, int datalen);
>  void ima_print_digest(struct seq_file *m, u8 *digest, u32 size);
>  struct ima_template_desc *ima_template_desc_current(void);
> +int ima_restore_measurement_entry(struct ima_template_entry *entry);
> +int ima_restore_measurement_list(loff_t bufsize, void *buf);
>  int ima_init_template(void);
>
>  /*
> diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
> index 2ac1f41db5c0..2967d497a665 100644
> --- a/security/integrity/ima/ima_init.c
> +++ b/security/integrity/ima/ima_init.c
> @@ -129,6 +129,8 @@ int __init ima_init(void)
>         if (rc != 0)
>                 return rc;
>
> +       ima_load_kexec_buffer();
> +
>         rc = ima_add_boot_aggregate();  /* boot aggregate must be first entry */
>         if (rc != 0)
>                 return rc;
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> new file mode 100644
> index 000000000000..36afd0fe9747
> --- /dev/null
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -0,0 +1,44 @@
> +/*
> + * Copyright (C) 2016 IBM Corporation
> + *
> + * Authors:
> + * Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxxxxxxx>
> + * Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> + *
> + * 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 "ima.h"
> +
> +/*
> + * Restore the measurement list from the previous kernel.
> + */
> +void ima_load_kexec_buffer(void)
> +{
> +       void *kexec_buffer = NULL;
> +       size_t kexec_buffer_size = 0;
> +       int rc;
> +
> +       rc = ima_get_kexec_buffer(&kexec_buffer, &kexec_buffer_size);
> +       switch (rc) {
> +       case 0:
> +               rc = ima_restore_measurement_list(kexec_buffer_size,
> +                                                 kexec_buffer);
> +               if (rc != 0)
> +                       pr_err("Failed to restore the measurement list: %d\n",
> +                               rc);
> +
> +               ima_free_kexec_buffer();
> +               break;
> +       case -ENOTSUPP:
> +               pr_debug("Restoring the measurement list not supported\n");
> +               break;
> +       case -ENOENT:
> +               pr_debug("No measurement list to restore\n");
> +               break;
> +       default:
> +               pr_debug("Error restoring the measurement list: %d\n", rc);
> +       }
> +}
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index 32f6ac0f96df..4b1bb7787839 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -149,3 +149,13 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>                             op, audit_cause, result, audit_info);
>         return result;
>  }
> +
> +int ima_restore_measurement_entry(struct ima_template_entry *entry)
> +{
> +       int result = 0;
> +
> +       mutex_lock(&ima_extend_list_mutex);
> +       result = ima_add_digest_entry(entry);
> +       mutex_unlock(&ima_extend_list_mutex);
> +       return result;
> +}
> diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
> index febd12ed9b55..7556a61db483 100644
> --- a/security/integrity/ima/ima_template.c
> +++ b/security/integrity/ima/ima_template.c
> @@ -37,6 +37,7 @@ static struct ima_template_field supported_fields[] = {
>         {.field_id = "sig", .field_init = ima_eventsig_init,
>          .field_show = ima_show_template_sig},
>  };
> +#define MAX_TEMPLATE_NAME_LEN 15
>
>  static struct ima_template_desc *ima_template;
>  static struct ima_template_desc *lookup_template_desc(const char *name);
> @@ -205,3 +206,179 @@ int __init ima_init_template(void)
>
>         return result;
>  }
> +
> +static int ima_restore_template_data(struct ima_template_desc *template_desc,
> +                                    void *template_data,
> +                                    int template_data_size,
> +                                    struct ima_template_entry **entry)
> +{
> +       struct binary_field_data {
> +               u32 len;
> +               u8 data[0];
> +       } __packed;
> +
> +       struct binary_field_data *field_data;
> +       int offset = 0;
> +       int ret = 0;
> +       int i;
> +
> +       *entry = kzalloc(sizeof(**entry) +
> +                   template_desc->num_fields * sizeof(struct ima_field_data),
> +                   GFP_NOFS);
> +       if (!*entry)
> +               return -ENOMEM;
> +
> +       (*entry)->template_desc = template_desc;
> +       for (i = 0; i < template_desc->num_fields; i++) {
> +               field_data = template_data + offset;
> +
> +               /* Each field of the template data is prefixed with a length. */
> +               if (offset > (template_data_size - sizeof(field_data->len))) {
> +                       pr_err("Restoring the template field failed\n");
> +                       ret = -EINVAL;
> +                       break;
> +               }

Looks a lot cleaner. But sizeof(field_data->len) is assumption that
field data header has just len.
Indeed it is currently, but isn't it better: sizeof(*field_data)


> +               offset += sizeof(field_data->len);
> +
> +               if (offset > (template_data_size - field_data->len)) {
> +                       pr_err("Restoring the template field data failed\n");
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +               offset += field_data->len;
> +
> +               (*entry)->template_data[i].len = field_data->len;
> +               (*entry)->template_data_len += sizeof(field_data->len);
> +
> +               (*entry)->template_data[i].data =
> +                       kzalloc(field_data->len + 1, GFP_KERNEL);
> +               if (!(*entry)->template_data[i].data) {
> +                       ret = -ENOMEM;
> +                       break;
> +               }
> +               memcpy((*entry)->template_data[i].data, field_data->data,
> +                       field_data->len);
> +               (*entry)->template_data_len += field_data->len;
> +       }
> +
> +       if (ret < 0) {
> +               ima_free_template_entry(*entry);
> +               *entry = NULL;
> +       }
> +
> +       return ret;
> +}
> +
> +/* Restore the serialized binary measurement list without extending PCRs. */
> +int ima_restore_measurement_list(loff_t size, void *buf)
> +{
> +       struct binary_hdr_v1 {
> +               u32 pcr;
> +               u8 digest[TPM_DIGEST_SIZE];
> +               u32 template_name_len;
> +               char template_name[0];
> +       } __packed;
> +       char template_name[MAX_TEMPLATE_NAME_LEN];
> +
> +       struct binary_data_v1 {
> +               u32 template_data_size;
> +               char template_data[0];
> +       } __packed;
> +
> +       struct ima_kexec_hdr *khdr = buf;
> +       struct binary_hdr_v1 *hdr_v1;
> +       struct binary_data_v1 *data_v1;
> +
> +       void *bufp = buf + sizeof(*khdr);
> +       void *bufendp = buf + khdr->buffer_size;
> +       struct ima_template_entry *entry;
> +       struct ima_template_desc *template_desc;
> +       unsigned long count = 0;
> +       int ret = 0;
> +
> +       if (!buf || size < sizeof(*khdr))
> +               return 0;
> +
> +       if (khdr->version != 1) {
> +               pr_err("attempting to restore a incompatible measurement list");
> +               return -EINVAL;
> +       }
> +
> +       if (khdr->count > ULONG_MAX - 1) {
> +               pr_err("attempting to restore too many measurements");
> +               return -EINVAL;
> +       }
> +
> +       /*
> +        * ima kexec buffer prefix: version, buffer size, count
> +        * v1 format: pcr, digest, template-name-len, template-name,
> +        *            template-data-size, template-data
> +        */
> +       while ((bufp < bufendp) && (count++ < khdr->count)) {
> +               hdr_v1 = bufp;
> +               if (bufp > (bufendp - sizeof(*hdr_v1))) {
> +                       pr_err("attempting to restore partial measurement\n");
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +               bufp += sizeof(*hdr_v1);
> +
> +               if ((hdr_v1->template_name_len >= MAX_TEMPLATE_NAME_LEN) ||
> +                   (bufp > (bufendp - hdr_v1->template_name_len))) {
> +                       pr_err("attempting to restore a template name \
> +                               that is too long\n");
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +               data_v1 = bufp += (u_int8_t)hdr_v1->template_name_len;
> +
> +               /* template name is not null terminated */
> +               memcpy(template_name, hdr_v1->template_name,
> +                      hdr_v1->template_name_len);
> +               template_name[hdr_v1->template_name_len] = 0;
> +
> +               if (strcmp(template_name, "ima") == 0) {
> +                       pr_err("attempting to restore an unsupported \
> +                               template \"%s\" failed\n", template_name);
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +
> +               /* get template format */
> +               template_desc = lookup_template_desc(template_name);
> +               if (!template_desc) {
> +                       pr_err("template \"%s\" not found\n", template_name);
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +
> +               if (bufp > (bufendp - sizeof(data_v1->template_data_size))) {
> +                       pr_err("restoring the template data size failed\n");
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +               bufp += (u_int8_t) sizeof(data_v1->template_data_size);
> +
> +               if (bufp > (bufendp - data_v1->template_data_size)) {
> +                       pr_err("restoring the template data failed\n");
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +               bufp += data_v1->template_data_size;
> +
> +               ret = ima_restore_template_data(template_desc,
> +                                               data_v1->template_data,
> +                                               data_v1->template_data_size,
> +                                               &entry);
> +               if (ret < 0)
> +                       break;
> +
> +               memcpy(entry->digest, hdr_v1->digest, TPM_DIGEST_SIZE);
> +               entry->pcr = hdr_v1->pcr;
> +               ret = ima_restore_measurement_entry(entry);
> +               if (ret < 0)
> +                       break;
> +
> +       }
> +       return ret;
> +}
> --
> 2.1.0
>



Looks good.

-- 
Thanks,
Dmitry