linux-kernel - Re: [PATCH] of: Prevent unaligned access in of_alias

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Message-ID: <CACxGe6secYUbnZYCpoZH44nEDAU7chfzjxehxWyyotSQE7fWHg@mail.gmail.com>
Date:   Fri, 23 Sep 2016 17:13:32 +0100
From:   Grant Likely <grant.likely@...retlab.ca>
To:     Paul Burton <paul.burton@...tec.com>
Cc:     linux-mips <linux-mips@...ux-mips.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH] of: Prevent unaligned access in of_alias_scan()

On Fri, Sep 23, 2016 at 4:38 PM, Paul Burton <paul.burton@...tec.com> wrote:
> When allocating a struct alias_prop, of_alias_scan() only requested that
> it be aligned on a 4 byte boundary. The struct contains pointers which
> leads to us attempting 64 bit writes on 64 bit systems, and if the CPU
> doesn't support unaligned memory accesses then this causes problems -
> for example on some MIPS64r2 CPUs including the "mips64r2-generic" QEMU
> emulated CPU it will trigger an address error exception.
>
> Fix this by requesting alignment for the struct alias_prop allocation
> matching that which the compiler expects, using the __alignof__ keyword.
>
> Signed-off-by: Paul Burton <paul.burton@...tec.com>

Looks right to me.

Reviewed-by: Grant Likely <grant.likely@...retlab.ca>

> Cc: devicetree@...r.kernel.org
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Frank Rowand <frowand.list@...il.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mips@...ux-mips.org
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> ---
>  drivers/of/base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 3ce6953..448aa40 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -2042,7 +2042,7 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align))
>                         continue;
>
>                 /* Allocate an alias_prop with enough space for the stem */
> -               ap = dt_alloc(sizeof(*ap) + len + 1, 4);
> +               ap = dt_alloc(sizeof(*ap) + len + 1, __alignof__(*ap));
>                 if (!ap)
>                         continue;
>                 memset(ap, 0, sizeof(*ap) + len + 1);
> --
> 2.10.0
>