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Message-Id: <1478639004.2879.210.camel@linux.vnet.ibm.com>
Date: Tue, 08 Nov 2016 16:03:24 -0500
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
linux-security-module <linux-security-module@...r.kernel.org>,
linuxppc-dev@...ts.ozlabs.org, kexec@...ts.infradead.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
linux-ima-devel <linux-ima-devel@...ts.sourceforge.net>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Linux-ima-devel] [PATCH v6 04/10] ima: maintain memory size
needed for serializing the measurement list
On Tue, 2016-11-08 at 22:05 +0200, Dmitry Kasatkin wrote:
> On Fri, Oct 21, 2016 at 5:44 AM, Thiago Jung Bauermann
> <bauerman@...ux.vnet.ibm.com> wrote:
> > From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> >
> > In preparation for serializing the binary_runtime_measurements, this patch
> > maintains the amount of memory required.
> >
> > Changelog v5:
> > - replace CONFIG_KEXEC_FILE with architecture CONFIG_HAVE_IMA_KEXEC (Thiago)
> >
> > Changelog v3:
> > - include the ima_kexec_hdr size in the binary_runtime_measurement size.
> >
> > Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> > ---
> > security/integrity/ima/Kconfig | 12 +++++++++
> > security/integrity/ima/ima.h | 1 +
> > security/integrity/ima/ima_queue.c | 53 ++++++++++++++++++++++++++++++++++++--
> > 3 files changed, 64 insertions(+), 2 deletions(-)
> >
> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > index 5487827fa86c..370eb2f4dd37 100644
> > --- a/security/integrity/ima/Kconfig
> > +++ b/security/integrity/ima/Kconfig
> > @@ -27,6 +27,18 @@ config IMA
> > to learn more about IMA.
> > If unsure, say N.
> >
> > +config IMA_KEXEC
> > + bool "Enable carrying the IMA measurement list across a soft boot"
> > + depends on IMA && TCG_TPM && HAVE_IMA_KEXEC
> > + default n
> > + help
> > + TPM PCRs are only reset on a hard reboot. In order to validate
> > + a TPM's quote after a soft boot, the IMA measurement list of the
> > + running kernel must be saved and restored on boot.
> > +
> > + Depending on the IMA policy, the measurement list can grow to
> > + be very large.
> > +
> > config IMA_MEASURE_PCR_IDX
> > int
> > depends on IMA
> > diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> > index 51dc8d57d64d..ea1dcc452911 100644
> > --- a/security/integrity/ima/ima.h
> > +++ b/security/integrity/ima/ima.h
> > @@ -143,6 +143,7 @@ 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);
> > +unsigned long ima_get_binary_runtime_size(void);
> > int ima_init_template(void);
> >
> > /*
> > diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> > index 12d1b040bca9..3a3cc2a45645 100644
> > --- a/security/integrity/ima/ima_queue.c
> > +++ b/security/integrity/ima/ima_queue.c
> > @@ -29,6 +29,11 @@
> > #define AUDIT_CAUSE_LEN_MAX 32
> >
> > LIST_HEAD(ima_measurements); /* list of all measurements */
> > +#ifdef CONFIG_IMA_KEXEC
> > +static unsigned long binary_runtime_size;
> > +#else
> > +static unsigned long binary_runtime_size = ULONG_MAX;
> > +#endif
> >
> > /* key: inode (before secure-hashing a file) */
> > struct ima_h_table ima_htable = {
> > @@ -64,6 +69,24 @@ static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
> > return ret;
> > }
> >
> > +/*
> > + * Calculate the memory required for serializing a single
> > + * binary_runtime_measurement list entry, which contains a
> > + * couple of variable length fields (e.g template name and data).
> > + */
> > +static int get_binary_runtime_size(struct ima_template_entry *entry)
> > +{
> > + int size = 0;
> > +
> > + size += sizeof(u32); /* pcr */
> > + size += sizeof(entry->digest);
> > + size += sizeof(int); /* template name size field */
> > + size += strlen(entry->template_desc->name);
> > + size += sizeof(entry->template_data_len);
> > + size += entry->template_data_len;
> > + return size;
> > +}
> > +
>
> strlen returns len without '\0'. I cannot see how you would know how
> to read it back?
This function is used to keep a running memory size needed for
allocating the buffer to carry the measurement list across kexec.
Right, the memory need for the template name is +1.
Mimi
>
> > /* ima_add_template_entry helper function:
> > * - Add template entry to the measurement list and hash table, for
> > * all entries except those carried across kexec.
> > @@ -90,9 +113,30 @@ static int ima_add_digest_entry(struct ima_template_entry *entry, int flags)
> > key = ima_hash_key(entry->digest);
> > hlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]);
> > }
> > +
> > + if (binary_runtime_size != ULONG_MAX) {
> > + int size;
> > +
> > + size = get_binary_runtime_size(entry);
> > + binary_runtime_size = (binary_runtime_size < ULONG_MAX - size) ?
> > + binary_runtime_size + size : ULONG_MAX;
> > + }
> > return 0;
> > }
> >
> > +/*
> > + * Return the amount of memory required for serializing the
> > + * entire binary_runtime_measurement list, including the ima_kexec_hdr
> > + * structure.
> > + */
> > +unsigned long ima_get_binary_runtime_size(void)
> > +{
> > + if (binary_runtime_size >= (ULONG_MAX - sizeof(struct ima_kexec_hdr)))
> > + return ULONG_MAX;
> > + else
> > + return binary_runtime_size + sizeof(struct ima_kexec_hdr);
> > +};
> > +
> > static int ima_pcr_extend(const u8 *hash, int pcr)
> > {
> > int result = 0;
> > @@ -106,8 +150,13 @@ static int ima_pcr_extend(const u8 *hash, int pcr)
> > return result;
> > }
> >
> > -/* Add template entry to the measurement list and hash table,
> > - * and extend the pcr.
> > +/*
> > + * Add template entry to the measurement list and hash table, and
> > + * extend the pcr.
> > + *
> > + * On systems which support carrying the IMA measurement list across
> > + * kexec, maintain the total memory size required for serializing the
> > + * binary_runtime_measurements.
> > */
> > int ima_add_template_entry(struct ima_template_entry *entry, int violation,
> > const char *op, struct inode *inode,
> > --
> > 2.7.4
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