Messages in this thread | | | From | Keith Packard <> | Subject | [PATCH 0/2] ARM: support THREAD_INFO_IN_TASK (v7 only) (v2) | Date | Fri, 3 Sep 2021 23:09:05 -0700 |
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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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