linux-kernel - Re: [PATCH v2] lib: Use PFN_PHYS() in devmem_is

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Date:   Fri, 30 Jul 2021 12:36:47 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Liang Wang <wangliang101@...wei.com>
Cc:     palmerdabbelt@...gle.com, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, linux@...linux.org.uk,
        linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org,
        wangle6@...wei.com, kepler.chenxin@...wei.com,
        nixiaoming@...wei.com, wangkefeng.wang@...wei.com
Subject: Re: [PATCH v2] lib: Use PFN_PHYS() in devmem_is_allowed()

On Fri, Jul 30, 2021 at 03:43:15PM +0800, Liang Wang wrote:
> The physical address may exceed 32 bits on ARM(when ARM_LPAE enabled),
> use PFN_PHYS() in devmem_is_allowed(),

First off, good catch!

This should not be ARM specific, this should just say:

on 32-bit systems with more than 32 bits of physcial address

Also, towards then end then explain that in practice, yes,
this is probably just ARM which is affected. By explaining
this, it ensures folks are aware of the affected systems.

May be good to refer to commit 947d0496cf3e1 ("generic: make PFN_PHYS
explicitly return phys_addr_t") which added the original PFN_PHYS()
casting to phys_addr_t to resolve the same problem.

> or the physical address may overflow and be truncated.

Indeed. How did you find this issue? Can you describe that in the commit
log? Was it a real world issue or did you do just code inspection? Or
was there a bot which helped you?

> This bug was initially introduced from v2.6.37, and the function was moved
> to lib when v5.11.
> 
> Fixes: 087aaffcdf9c ("ARM: implement CONFIG_STRICT_DEVMEM by disabling access to RAM via /dev/mem")
> Fixes: 527701eda5f1 ("lib: Add a generic version of devmem_is_allowed()")
> Cc: stable@...r.kernel.org # v2.6.37
> Signed-off-by: Liang Wang <wangliang101@...wei.com>

Other than that:

Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>

  Luis