This adds support for KASLR is implemented, based on entropy provided by
the bootloader in the /chosen/kaslr-seed DT property. Depending on the size
of the address space (VA_BITS) and the page size, the entropy in the
virtual displacement is up to 13 bits (16k/2 levels) and up to 25 bits (all
4 levels), with the sidenote that displacements that result in the kernel
image straddling a 1GB/32MB/512MB alignment boundary (for 4KB/16KB/64KB
granule kernels, respectively) are not allowed, and will be rounded up to
an acceptable value.
If CONFIG_RANDOMIZE_MODULE_REGION_FULL is enabled, the module region is
randomized independently from the core kernel. This makes it less likely
that the location of core kernel data structures can be determined by an
adversary, but causes all function calls from modules into the core kernel
to be resolved via entries in the module PLTs.
If CONFIG_RANDOMIZE_MODULE_REGION_FULL is not enabled, the module region is
randomized by choosing a page aligned 128 MB region inside the interval
[_etext - 128 MB, _stext + 128 MB). This gives between 10 and 14 bits of
entropy (depending on page size), independently of the kernel randomization,
but still guarantees that modules are within the range of relative branch
and jump instructions (with the caveat that, since the module region is
shared with other uses of the vmalloc area, modules may need to be loaded
further away if the module region is exhausted)
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This adds support for emitting PLTs at module load time for relative
branches that are out of range. This is a prerequisite for KASLR, which
may place the kernel and the modules anywhere in the vmalloc area,
making it more likely that branch target offsets exceed the maximum
range of +/- 128 MB.
In this version, I removed the distinction between relocations against
.init executable sections and ordinary executable sections. The reason
is that it is hardly worth the trouble, given that .init.text usually
does not contain that many far branches, and this version now only
reserves PLT entry space for jump and call relocations against undefined
symbols (since symbols defined in the same module can be assumed to be
within +/- 128 MB)
For example, the mac80211.ko module (which is fairly sizable at ~400 KB)
built with -mcmodel=large gives the following relocation counts:
relocs branches unique !local
.text 3925 3347 518 219
.init.text 11 8 7 1
.exit.text 4 4 4 1
.text.unlikely 81 67 36 17
('unique' means branches to unique type/symbol/addend combos, of which
!local is the subset referring to undefined symbols)
IOW, we are only emitting a single PLT entry for the .init sections, and
we are better off just adding it to the core PLT section instead.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This patch adds support for loadable modules. Loadable modules are
loaded 64MB below the kernel image due to branch relocation restrictions
(see Documentation/arm64/memory.txt).
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Ard Biesheuvel