linux-kernel - Re: [PATCH -next] openrisc: Define __ro_after

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Message-ID: <9cbb8e34-01d1-e600-5ea0-f057d76cdc20@roeck-us.net>
Date:   Tue, 27 Sep 2016 07:41:51 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Stafford Horne <shorne@...il.com>
Cc:     Jonas Bonn <jonas@...thpole.se>, linux-kernel@...r.kernel.org,
        stefan.kristiansson@...nalahti.fi, akpm@...ux-foundation.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH -next] openrisc: Define __ro_after_init to avoid crash

On 09/27/2016 07:15 AM, Stafford Horne wrote:
>
>
> On Sat, 24 Sep 2016, Guenter Roeck wrote:
>
>> openrisc qemu tests fail with the following crash.
>>
>> Unable to handle kernel access at virtual address 0xc0300c34
>>
>> Oops#: 0001
>> CPU #: 0
>>   PC: c016c710    SR: 0000ae67    SP: c1017e04
>>   GPR00: 00000000 GPR01: c1017e04 GPR02: c0300c34 GPR03: c0300c34
>>   GPR04: 00000000 GPR05: c0300cb0 GPR06: c0300c34 GPR07: 000000ff
>>   GPR08: c107f074 GPR09: c0199ef4 GPR10: c1016000 GPR11: 00000000
>>   GPR12: 00000000 GPR13: c107f044 GPR14: c0473774 GPR15: 07ce0000
>>   GPR16: 00000000 GPR17: c107ed8a GPR18: 00009600 GPR19: c107f044
>>   GPR20: c107ee74 GPR21: 00000003 GPR22: c0473770 GPR23: 00000033
>>   GPR24: 000000bf GPR25: 00000019 GPR26: c046400c GPR27: 00000001
>>   GPR28: c0464028 GPR29: c1018000 GPR30: 00000006 GPR31: ccf37483
>>     RES: 00000000 oGPR11: ffffffff
>>     Process swapper (pid: 1, stackpage=c1001960)
>>
>>     Stack: Stack dump [0xc1017cf8]:
>>     sp + 00: 0xc1017e04
>>     sp + 04: 0xc0300c34
>>     sp + 08: 0xc0300c34
>>     sp + 12: 0x00000000
>> ...
>>
>> Bisect points to commit d2ec3f77de8e ("pty: make ptmx file ops read-only
>> after init"). Fix by defining __ro_after_init for the openrisc
>> architecture, similar to parisc.
>
> Thanks for finding this one.
> Just for clatify __read_mostly falls back to default blank in openrisc, so it gets no special section treatment.
>

Yes, I understand. It falls back to the pre-_ro_after_init behavior, which should be
perfectly fine here.

Guenter


> Acked-by: Stafford Horne <shorne@...il.com>
>
>
>> Fixes: d2ec3f77de8e ("pty: make ptmx file ops read-only after init")
>> Cc: Kees Cook <keescook@...omium.org>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>> arch/openrisc/include/asm/cache.h | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/openrisc/include/asm/cache.h b/arch/openrisc/include/asm/cache.h
>> index 4ce7a01a252d..5f55da9cbfd5 100644
>> --- a/arch/openrisc/include/asm/cache.h
>> +++ b/arch/openrisc/include/asm/cache.h
>> @@ -23,6 +23,8 @@
>>  * they shouldn't be hard-coded!
>>  */
>>
>> +#define __ro_after_init __read_mostly
>> +
>> #define L1_CACHE_BYTES 16
>> #define L1_CACHE_SHIFT 4
>>
>> --
>> 2.5.0
>>
>>
>