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List: linux-arm-kernel
Subject: [PATCH 0/2] ARM: support THREAD_INFO_IN_TASK (v7 only) (v2)
From: Keith Packard <keithp () keithp ! com>
Date: 2021-09-04 6:09:05
Message-ID: 20210904060908.1310204-1-keithp () keithp ! com
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Placing thread_info in the kernel stack leaves it vulnerable to stack
overflow attacks. This short series addresses that by using the
existing THREAD_INFO_IN_TASK infrastructure.
This is the second version of this series, in this version the changes
are restricted to v7 hardware which offers a way to identify each cpu
in the system without reference to the stack it is using.
The series is broken into three pieces:
1) Change the secondary_start_kernel API to pass the cpu number to
this function. This is required for the following patch because the
raw_smp_processor_id() macro will use the per_cpu_offset value which
needs to have the cpu number to get the right value.
2) Enable THREAD_INFO_IN_TASK by creating a new per-cpu variable,
current_task, just like the x86 architecture. The largest changes
are in the assembly code where fetching the current_task value
requires a temporary register. Fortunately, each location in the
code performing this had a reasonably obvious register to use.
3) Optimize access to the cpu number using another new per-cpu
variable. This is not functionally necessary, but avoids
de-referencing through two pointers at modest memory cost.
Signed-off-by: Keith Packard <keithpac@amazon.com>
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