Re: [PATCH 3/4] integrity: IMA as an integrity service provider

Mimi Zohar
2008-11-17T19:05:46Z

On Fri, 2008-11-14 at 14:15 -0800, Andrew Morton wrote:
> On Wed, 12 Nov 2008 22:47:13 -0500
> Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
>
> > This is a re-release of Integrity Measurement Architecture(IMA) as an
> > independent Linunx Integrity Module(LIM) service provider.
> >
> > As a LIM integrity provider, IMA implements the new LIM must_measure(),
> > collect_measurement(), store_measurement(), and display_template() API
> > calls. The store_measurement() call supports two types of data, IMA
> > (i.e. file data) and generic template data.
> >
> > IMA provides hardware (TPM) based measurement and attestation for both
> > files and other types of template measurements. As the Trusted Computing
> > (TPM) model requires, IMA measures all files before they are accessed
> > in any way (on the bprm_check_integrity, nameidata_check_integrity,
> > file_mmap hooks), and commits the measurements to the TPM. In addition,
> > IMA maintains a list of these hash values, which can be used to validate
> > the aggregate PCR value. The TPM can sign these measurements, and thus
> > the system can prove to itself and to a third party these measurements
> > in a way that cannot be circumvented by malicious or compromised software.
> >
> > When store_measurement() is called for the IMA type of data, the file
> > measurement and the file name hint are used to form an IMA template.
> > IMA then calculates the IMA template measurement(hash) and submits it
> > to the TPM chip for inclusion in one of the chip's Platform Configuration
> > Registers (PCR).
> >
> > When store_measurement() is called for generic template data, IMA
> > calculates the measurement(hash) of the template data, and submits
> > the template measurement to the TPM chip for inclusion in one of the
> > chip's Platform Configuration Registers(PCR).
> >
> > In order to view the contents of template data through securityfs, the
> > template_display() function must be defined in the registered
> > template_operations. In the case of the IMA template, the list of
> > file names and files hashes submitted can be viewed through securityfs.
> >
> > As mentioned above, IMA maintains a list of hash values of executables
> > and other sensitive system files loaded into the run-time of the system.
> > Our work has shown that requests for integrity appraisal and measurement
> > need to be based on knowledge of the filesystem, requiring the system
> > to either be labeled with integrity data or depend on the existent LSM
> > security labels. The previous set of integrity patches modified the LSM
> > modules to be integrity context aware, meaning that the LSM modules made
> > integrity data/metadata appraisal and measurement API calls based on
> > an understanding of the LSM security labels. Both of the LSM maintainers
> > felt that the changes were too intrusive and that integrity enforcement
> > should be made by the integrity provider, not the LSM module.
> >
> > To address these concerns, Stephen Smalley suggested using the
> > security_audit_rule_match(), renamed to security_filter_rule_match(), to
> > define LSM specific integrity measurement policy rules, in lieu of
> > modifying the LSM modules. In the current set of patches, the integrity
> > API calls can be made either by IMA, based on an LSM specific integrity
> > policy, or by an integrity context aware LSM.
> >
> > ...
> >
> > +static void ima_add_boot_aggregate(void)
> > +{
> > + /* cumulative sha1 over tpm registers 0-7 */
> > + struct ima_measure_entry *entry;
> > + size_t count;
> > + int err;
> > +
> > + /* create new entry for boot aggregate */
> > + entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
>
> This uses GFP_ATOMIC, but crypto_alloc_hash() (called later) uses
> GFP_KERNEL.
>
> If this _had_ to be GFP_ATOMIC then you have a bug.

Sorry, thought I fixed this.

> Otherwise, please use the much more reliable GFP_KERNEL here.