pstore/ram: Fix crash when setting number of cpus to an odd number

mainline inclusion
from mainline-v6.8-rc1
commit d49270a04623ce3c0afddbf3e984cb245aa48e9c
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I99JQV
CVE: CVE-2023-52619

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d49270a04623ce3c0afddbf3e984cb245aa48e9c



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When the number of cpu cores is adjusted to 7 or other odd numbers,
the zone size will become an odd number.
The address of the zone will become:
    addr of zone0 = BASE
    addr of zone1 = BASE + zone_size
    addr of zone2 = BASE + zone_size*2
    ...
The address of zone1/3/5/7 will be mapped to non-alignment va.
Eventually crashes will occur when accessing these va.

So, use ALIGN_DOWN() to make sure the zone size is even
to avoid this bug.

Fixes: de832092 ("pstore: Make ramoops_init_przs generic for other prz arrays")
Signed-off-by: Weichen Chen <weichen.chen@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Tested-by: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Link: https://lore.kernel.org/r/20230224023632.6840-1-weichen.chen@mediatek.com


Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Zeng Heng <zengheng4@huawei.com>