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| author |   Jason Yan <yanaijie@huawei.com> | 2019-09-20 17:45:46 +0800 |
|---|---|---|
| committer |   Michael Ellerman <mpe@ellerman.id.au> | 2019-11-13 19:27:58 +1100 |
| commit | c2d1a13520eee7f0ac64ffb94f8756006320e4b8 (patch) | |
| tree | 3d0c6ab3c5d5005a821bfdec40a02ad32e87b593 /Documentation/powerpc | |
| parent | powerpc/fsl_booke/kaslr: export offset in VMCOREINFO ELF notes (diff) | |
| download | wireguard-linux-c2d1a13520eee7f0ac64ffb94f8756006320e4b8.tar.xz wireguard-linux-c2d1a13520eee7f0ac64ffb94f8756006320e4b8.zip | |
powerpc/fsl_booke/32: Document KASLR implementation
Add document to explain how we implement KASLR for fsl_booke32.
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Scott Wood <oss@buserror.net>
[mpe: Add it to the index as well]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'Documentation/powerpc')
| -rw-r--r-- | Documentation/powerpc/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/powerpc/kaslr-booke32.rst | 42 |
2 files changed, 43 insertions, 0 deletions
diff --git a/Documentation/powerpc/index.rst b/Documentation/powerpc/index.rst index db7b6a880f52..ba5edb3211c0 100644 --- a/Documentation/powerpc/index.rst +++ b/Documentation/powerpc/index.rst @@ -19,6 +19,7 @@ powerpc firmware-assisted-dump hvcs isa-versions + kaslr-booke32 mpc52xx pci_iov_resource_on_powernv pmu-ebb diff --git a/Documentation/powerpc/kaslr-booke32.rst b/Documentation/powerpc/kaslr-booke32.rst new file mode 100644 index 000000000000..8b259fdfdf03 --- /dev/null +++ b/Documentation/powerpc/kaslr-booke32.rst @@ -0,0 +1,42 @@ +.. 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 enable and you +want to disable it at runtime, add "nokaslr" to the kernel cmdline. |