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The "ground truth" stack protector cookie value is kept in a global variable, and loaded in every function prologue and epilogue to store it into resp. compare it with the stack slot holding the cookie. If the comparison fails, the program aborts, and this might occur spuriously when the global variable changes values between the entry and exit of a function. This implies that assigning the global variable at boot should not involve any instrumented function calls, unless special care is taken to ensure that the live call stack is synchronized, which is non-trivial. So avoid any function calls, including grub_memcpy(), which is unnecessary given that the stack cookie is always a suitably aligned variable of the native word size. While at it, leave the last byte 0x0 to avoid inadvertent unbounded strings on the stack. Note that the use of __attribute__((optimize)) is described as unsuitable for production use in the GCC documentation, so let's drop this as well now that it is no longer needed. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> 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'