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The vDSO (and its initial randomization) was introduced in commit2aae950b21("x86_64: Add vDSO for x86-64 with gettimeofday/clock_gettime/getcpu"), but had very low entropy. The entropy was improved in commit394f56fe48("x86_64, vdso: Fix the vdso address randomization algorithm"), but there is still improvement to be made. In principle there should not be executable code at a low entropy offset from the stack, since the stack and executable code having separate randomization is part of what makes ASLR stronger. Remove the only executable code near the stack region and give the vDSO the same randomized base as other mmap mappings including the linker and other shared objects. This results in higher entropy being provided and there's little to no advantage in separating this from the existing executable code there. This is already how other architectures like arm64 handle the vDSO. As an side, while it's sensible for userspace to reserve the initial mmap base as a region for executable code with a random gap for other mmap allocations, along with providing randomization within that region, there isn't much the kernel can do to help due to how dynamic linkers load the shared objects. This was extracted from the PaX RANDMMAP feature. [kees: updated commit log with historical details and other tweaks] Signed-off-by: Daniel Micay <danielmicay@gmail.com> Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Closes: https://github.com/KSPP/linux/issues/280 Link: https://lore.kernel.org/r/20240210091827.work.233-kees@kernel.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.