lkml.org 
[lkml]   [2022]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] [PATCH v4] arm64/mm: avoid fixmap race condition when create pud mapping
On Tue, Feb 01, 2022 at 07:44:00PM +0800, Jianyong Wu wrote:
> The 'fixmap' is a global resource and is used recursively by
> create pud mapping(), leading to a potential race condition in the
> presence of a concurrent call to alloc_init_pud():
>
> kernel_init thread virtio-mem workqueue thread
> ================== ===========================
>
> alloc_init_pud(...) alloc_init_pud(...)
> pudp = pud_set_fixmap_offset(...) pudp = pud_set_fixmap_offset(...)
> READ_ONCE(*pudp)
> pud_clear_fixmap(...)
> READ_ONCE(*pudp) // CRASH!
>
> As kernel may sleep during creating pud mapping, introduce a mutex lock to
> serialise use of the fixmap entries by alloc_init_pud(). However, there is
> no need for locking in early boot stage and it doesn't work well with
> KASLR enabled when early boot. So, enable lock when system_state doesn't
> equal to "SYSTEM_BOOTING".
>
> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

This looks fine to me but I'd rather leave it in -next for a bit given
that we attempted to fix it a couple of times and got it wrong.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

\
 
 \ /
  Last update: 2022-02-04 19:44    [W:0.050 / U:0.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site