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diff --git a/Documentation/powerpc/kaslr-booke32.rst b/Documentation/powerpc/kaslr-booke32.rst deleted file mode 100644 index 5681c1d1b6..0000000000 --- a/Documentation/powerpc/kaslr-booke32.rst +++ /dev/null @@ -1,42 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -=========================== -KASLR for Freescale BookE32 -=========================== - -The word KASLR stands for Kernel Address Space Layout Randomization. - -This document tries to explain the implementation of the KASLR for -Freescale BookE32. KASLR is a security feature that deters exploit -attempts relying on knowledge of the location of kernel internals. - -Since CONFIG_RELOCATABLE has already supported, what we need to do is -map or copy kernel to a proper place and relocate. Freescale Book-E -parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1 -entries are not suitable to map the kernel directly in a randomized -region, so we chose to copy the kernel to a proper place and restart to -relocate. - -Entropy is derived from the banner and timer base, which will change every -build and boot. This not so much safe so additionally the bootloader may -pass entropy via the /chosen/kaslr-seed node in device tree. - -We will use the first 512M of the low memory to randomize the kernel -image. The memory will be split in 64M zones. We will use the lower 8 -bit of the entropy to decide the index of the 64M zone. Then we chose a -16K aligned offset inside the 64M zone to put the kernel in:: - - KERNELBASE - - |--> 64M <--| - | | - +---------------+ +----------------+---------------+ - | |....| |kernel| | | - +---------------+ +----------------+---------------+ - | | - |-----> offset <-----| - - kernstart_virt_addr - -To enable KASLR, set CONFIG_RANDOMIZE_BASE = y. If KASLR is enabled and you -want to disable it at runtime, add "nokaslr" to the kernel cmdline. |