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

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Date:   Tue, 27 Sep 2016 23:15:56 +0900 (JST)
From:   Stafford Horne <shorne@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
cc:     Jonas Bonn <jonas@...thpole.se>, linux-kernel@...r.kernel.org,
        shorne@...il.com, 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 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.

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
>
>