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ANDROID: gki_defconfig: reduce KFENCE pool size

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CONFIG_KFENCE_NUM_OBJECTS controls the constant memory overhead that
KFENCE introduces for its memory pool. By default it is 255 objects
(2Mb extra memory), but since concerns have been raised that low-memory
devices may not afford that, we are lowering the number of objects
to 63 (512Kb extra memory).

So far we haven't seen Android devices allocate more than 50 KFENCE
objects. Should the kernel exhaust the pool, KFENCE will stop allocating
new objects and fall back to SLAB/SLUB until one of the objects is
freed.

An immediate consequence of reducing the pool size is that a freed
KFENCE object will be reused 4x times faster, effectively reducing the
probability of detecting a use-after-free. Since KFENCE is a best-effort
error detection tool, not a use-after-free mitigation mechanism, we
believe this should not be problematic.

Bug: 181822795
Test: run KFENCE on an Android device
Signed-off-by: Alexander Potapenko <glider@google.com>
Change-Id: I88fca80eea8b382115de03dbb104fd305b35476f
This commit is contained in:
Alexander Potapenko 2021-04-13 16:22:45 +02:00 • committed by Michael Bestas
commit a8ef4f11e4
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2 changed files with 2 additions and 0 deletions
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1
arch/arm64/configs/gki_defconfig
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@ -604,6 +604,7 @@ CONFIG_DEBUG_STACK_USAGE=y
CONFIG_DEBUG_MEMORY_INIT=y
CONFIG_KFENCE=y
CONFIG_KFENCE_SAMPLE_INTERVAL=500
CONFIG_KFENCE_NUM_OBJECTS=63
CONFIG_SOFTLOCKUP_DETECTOR=y
# CONFIG_DETECT_HUNG_TASK is not set
CONFIG_PANIC_ON_OOPS=y

1
arch/x86/configs/gki_defconfig
View file

@ -535,6 +535,7 @@ CONFIG_DEBUG_STACK_USAGE=y
CONFIG_DEBUG_MEMORY_INIT=y
CONFIG_KFENCE=y
CONFIG_KFENCE_SAMPLE_INTERVAL=500
CONFIG_KFENCE_NUM_OBJECTS=63
CONFIG_SOFTLOCKUP_DETECTOR=y
# CONFIG_DETECT_HUNG_TASK is not set
CONFIG_PANIC_ON_OOPS=y