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The canary, __stack_chk_guard, is in the BSS and so will get initialized to zero if it is not explicitly initialized. If the UEFI firmware does not support the RNG protocol, then the canary will not be randomized and will be zero. This seems like a possibly easier value to write by an attacker. Initialize canary to static random bytes, so that it is still random when there is no RNG protocol. Set at least one byte to NUL to protect against string buffer overflow attacks [1]. Code that writes NUL terminated strings will terminate when a NUL is encountered in the input byte stream. So the attacker will not be able to forge the canary by including it in the input stream without terminating the string operation and thus limiting the stack corruption. [1] https://www.sans.org/blog/stack-canaries-gingerly-sidestepping-the-cage/ Signed-off-by: Glenn Washburn <development@efficientek.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'