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arm64: fix the doc of RANDOMIZE_MODULE_REGION_FULL

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Obviously kaslr is setting the module region to 2GB rather than 4GB since
commit b2eed9b588 ("arm64/kernel: kaslr: reduce module randomization
range to 2 GB"). So fix the size of region in Kconfig.
On the other hand, even though RANDOMIZE_MODULE_REGION_FULL is not set,
module_alloc() can fall back to a 2GB window if ARM64_MODULE_PLTS is set.
In this case, veneers are still needed. !RANDOMIZE_MODULE_REGION_FULL
doesn't necessarily mean veneers are not needed.
So fix the doc to be more precise to avoid any confusion to the readers
of the code.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Qi Liu <liuqi115@huawei.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20210730125131.13724-1-song.bao.hua@hisilicon.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Barry Song 2021-07-31 00:51:31 +12:00 committed by Will Deacon
parent 64ee84c75b
commit f9c4ff2ab9
2 changed files with 9 additions and 4 deletions
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9
arch/arm64/Kconfig
View File

@ -1800,11 +1800,11 @@ config RANDOMIZE_BASE
If unsure, say N.
config RANDOMIZE_MODULE_REGION_FULL
bool "Randomize the module region over a 4 GB range"
bool "Randomize the module region over a 2 GB range"
depends on RANDOMIZE_BASE
default y
help
Randomizes the location of the module region inside a 4 GB window
Randomizes the location of the module region inside a 2 GB window
covering the core kernel. This way, it is less likely for modules
to leak information about the location of core kernel data structures
but it does imply that function calls between modules and the core
@ -1812,7 +1812,10 @@ config RANDOMIZE_MODULE_REGION_FULL
When this option is not set, the module region will be randomized over
a limited range that contains the [_stext, _etext] interval of the
core kernel, so branch relocations are always in range.
core kernel, so branch relocations are almost always in range unless
ARM64_MODULE_PLTS is enabled and the region is exhausted. In this
particular case of region exhaustion, modules might be able to fall
back to a larger 2GB area.
config CC_HAVE_STACKPROTECTOR_SYSREG
def_bool $(cc-option,-mstack-protector-guard=sysreg -mstack-protector-guard-reg=sp_el0 -mstack-protector-guard-offset=0)

4
arch/arm64/kernel/kaslr.c
View File

@ -162,7 +162,9 @@ u64 __init kaslr_early_init(void)
* a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
* _stext) . This guarantees that the resulting region still
* covers [_stext, _etext], and that all relative branches can
* be resolved without veneers.
* be resolved without veneers unless this region is exhausted
* and we fall back to a larger 2GB window in module_alloc()
* when ARM64_MODULE_PLTS is enabled.
*/
module_range = MODULES_VSIZE - (u64)(_etext - _stext);
module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;