linux-kernel - Re: [PATCH 1/5] lib: Add a generic version of devmem_is

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 10 Jul 2020 08:48:17 +0300
From:   Nick Kossifidis <mick@....forth.gr>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>, mark.rutland@....com,
        steve@....org, gregory.0xf0@...il.com, catalin.marinas@....com,
        linus.walleij@...aro.org,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        zaslonko@...ux.ibm.com, glider@...gle.com, krzk@...nel.org,
        zong.li@...ive.com, mchehab+samsung@...nel.org,
        linux-riscv@...ts.infradead.org, alex.shi@...ux.alibaba.com,
        will@...nel.org, ardb@...nel.org, linux-arch@...r.kernel.org,
        paulmck@...nel.org, alex@...ti.fr, bgolaszewski@...libre.com,
        masahiroy@...nel.org, linux@...linux.org.uk, willy@...radead.org,
        takahiro.akashi@...aro.org, james.morse@....com,
        kernel-team@...roid.com, Arnd Bergmann <arnd@...db.de>,
        pmladek@...e.com, elver@...gle.com, aou@...s.berkeley.edu,
        keescook@...omium.org, uwe@...ine-koenig.org, rostedt@...dmis.org,
        broonie@...nel.org, davidgow@...gle.com,
        Paul Walmsley <paul.walmsley@...ive.com>,
        dan.j.williams@...el.com, andriy.shevchenko@...ux.intel.com,
        gxt@....edu.cn, linux-arm-kernel@...ts.infradead.org,
        Nick Desaulniers <ndesaulniers@...gle.com>, tglx@...utronix.de,
        rdunlap@...radead.org, matti.vaittinen@...rohmeurope.com,
        linux-kernel@...r.kernel.org, mcgrof@...nel.org,
        Palmer Dabbelt <palmer@...belt.com>, mhiramat@...nel.org,
        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [PATCH 1/5] lib: Add a generic version of devmem_is_allowed()

Στις 2020-07-10 08:38, Christoph Hellwig έγραψε:
> On Thu, Jul 09, 2020 at 11:49:21PM +0300, Mike Rapoport wrote:
>> > +#ifndef CONFIG_GENERIC_DEVMEM_IS_ALLOWED
>> > +extern int devmem_is_allowed(unsigned long pfn);
>> > +#endif
> 
> Nit: no need for the extern here.
> 
>> > +config GENERIC_LIB_DEVMEM_IS_ALLOWED
>> > +	bool
>> > +	select ARCH_HAS_DEVMEM_IS_ALLOWED
>> 
>> This seems to work the other way around from the usual Kconfig chains.
>> In the most cases ARCH_HAS_SOMETHING selects GENERIC_SOMETHING.
>> 
>> I believe nicer way would be to make
>> 
>> config STRICT_DEVMEM
>> 	bool "Filter access to /dev/mem"
>> 	depends on MMU && DEVMEM
>> 	depends on ARCH_HAS_DEVMEM_IS_ALLOWED || 
>> GENERIC_LIB_DEVMEM_IS_ALLOWED
>> 
>> config GENERIC_LIB_DEVMEM_IS_ALLOWED
>> 	bool
>> 
>> and then s/select ARCH_HAS_DEVMEM_IS_ALLOWED/select 
>> GENERIC_LIB_DEVMEM_IS_ALLOWED/
>> in the arch Kconfigs and drop ARCH_HAS_DEVMEM_IS_ALLOWED in the end.
> 
> To take a step back:  Is there any reason to not just always
> STRICT_DEVMEM? Maybe for a few architectures that don't currently
> support a strict /dev/mem the generic version isn't quite correct, but
> someone selecting the option and finding the issue is the best way to
> figure that out..
> 

During prototyping / testing having full access to all physical memory 
through /dev/mem is very useful. We should have it enabled by default 
but leave the config option there so that users / developers can disable 
it if needed IMHO.