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When the tpm module is loaded, the verifier reads entire file into memory, measures it and uses verified content as a backing buffer for file accesses. However, this process may result in high memory utilization for file operations, sometimes causing a system to run out of memory which may finally lead to boot failure. To address this issue, among others, the commit 887f98f0d (mm: Allow dynamically requesting additional memory regions) have optimized memory management by dynamically allocating heap space to maximize memory usage and reduce threat of memory exhaustion. But in some cases problems may still arise, e.g., when large ISO images are mounted using loopback or when dealing with embedded systems with limited memory resources. Unfortunately current implementation of the tpm module doesn't allow elimination of the back buffer once it is loaded. Even if the TPM device is not present or it has been explicitly disabled. This may unnecessary allocate a lot memory. To solve this issue, a patch has been developed to detect the TPM status at module load and skip verifier registration if the device is missing or deactivated. This prevents allocation of memory for the back buffer, avoiding wasting memory when no real measure boot functionality is performed. Disabling the TPM device in the system can reduce memory usage in the GRUB. It is useful in scenarios where high memory utilization is a concern and measurements of loaded artifacts are not necessary. Signed-off-by: Michael Chang <mchang@suse.com> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'