[PATCH] arm64: Fix KASAN random tag seed initialization

[Catalin Marinas]

On Wed, Aug 14, 2024 at 02:09:53AM -0700, Samuel Holland wrote:
> Currently, kasan_init_sw_tags() is called before setup_per_cpu_areas(),
> so per_cpu(prng_state, cpu) accesses the same address regardless of the
> value of "cpu", and the same seed value gets copied to the percpu area
> for every CPU. Fix this by moving the call to smp_prepare_boot_cpu(),
> which is the first architecture hook after setup_per_cpu_areas().

Even with the fix, given the lower resolution of get_cycles(), there's a
good chance that we still have the same seed on all CPUs. If we want
separate seeds, a better bet would be to initialise each CPU separately
via the secondary_start_kernel() path. I'll let the KASAN people comment
on whether that's important.

-- 
Catalin