x86, kaslr: Clarify RANDOMIZE_BASE_MAX_OFFSET
The help text for RANDOMIZE_BASE_MAX_OFFSET was confusing. This has been clarified, and updated to be an export-only tunable. Signed-off-by: Kees Cook <keescook@chromium.org> Link: http://lkml.kernel.org/r/20131210202745.GA2961@www.outflux.net Acked-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
parent
19259943f0
commit
da2b6fb990
|
@ -1747,26 +1747,33 @@ config RANDOMIZE_BASE
|
|||
possible. At best, due to page table layouts, 64-bit can use
|
||||
9 bits of entropy and 32-bit uses 8 bits.
|
||||
|
||||
If unsure, say N.
|
||||
|
||||
config RANDOMIZE_BASE_MAX_OFFSET
|
||||
hex "Maximum ASLR offset allowed"
|
||||
hex "Maximum kASLR offset allowed" if EXPERT
|
||||
depends on RANDOMIZE_BASE
|
||||
range 0x0 0x20000000 if X86_32
|
||||
default "0x20000000" if X86_32
|
||||
range 0x0 0x40000000 if X86_64
|
||||
default "0x40000000" if X86_64
|
||||
---help---
|
||||
Determines the maximal offset in bytes that will be applied to the
|
||||
kernel when Address Space Layout Randomization (ASLR) is active.
|
||||
Must be less than or equal to the actual physical memory on the
|
||||
system. This must be a multiple of CONFIG_PHYSICAL_ALIGN.
|
||||
The lesser of RANDOMIZE_BASE_MAX_OFFSET and available physical
|
||||
memory is used to determine the maximal offset in bytes that will
|
||||
be applied to the kernel when kernel Address Space Layout
|
||||
Randomization (kASLR) is active. This must be a multiple of
|
||||
PHYSICAL_ALIGN.
|
||||
|
||||
On 32-bit this is limited to 512MiB.
|
||||
On 32-bit this is limited to 512MiB by page table layouts. The
|
||||
default is 512MiB.
|
||||
|
||||
On 64-bit this is limited by how the kernel fixmap page table is
|
||||
positioned, so this cannot be larger that 1GiB currently. Normally
|
||||
there is a 512MiB to 1.5GiB split between kernel and modules. When
|
||||
this is raised above the 512MiB default, the modules area will
|
||||
shrink to compensate, up to the current maximum 1GiB to 1GiB split.
|
||||
On 64-bit this is limited by how the kernel fixmap page table is
|
||||
positioned, so this cannot be larger than 1GiB currently. Without
|
||||
RANDOMIZE_BASE, there is a 512MiB to 1.5GiB split between kernel
|
||||
and modules. When RANDOMIZE_BASE_MAX_OFFSET is above 512MiB, the
|
||||
modules area will shrink to compensate, up to the current maximum
|
||||
1GiB to 1GiB split. The default is 1GiB.
|
||||
|
||||
If unsure, leave at the default value.
|
||||
|
||||
# Relocation on x86 needs some additional build support
|
||||
config X86_NEED_RELOCS
|
||||
|
|
Loading…
Reference in a new issue