Re: [Xen-devel] [PATCH] xen: arm: Update arm64 image header

[Julien Grall <julien.grall@xxxxxxx>]

Hello Dirk,

On 21/06/16 10:08, Dirk Behme wrote:
> With the Linux kernel commits
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/Documentation/arm64/booting.txt?id=4370eec05a887b0cd4392cd5dc5b2713174745c0
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/Documentation/arm64/booting.txt?id=a2c1d73b94ed49f5fac12e95052d7b140783f800
>
> the arm64 image header changed. While the size of the header isn't changed,
> some members have changed their usage.
>
> Update Xen to this updated image header.
>
> The main changes are that the first magic is gone and that there is an
> image size, now.
Whilst the first magic is gone in the new version of the header, older 
kernel will still use it. So we have to support them.
> In case we read a size != 0, let's use this image size, now. This does
> allow us to warn if the kernel Image is larger than the size given in
> the device tree, too.
Based on the code below, you don't warn but return an error.

> Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
> ---
>   xen/arch/arm/kernel.c | 41 ++++++++++++++++++++++++-----------------
>   1 file changed, 24 insertions(+), 17 deletions(-)
>
> diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c
> index 3f6cce3..1cfaf02 100644
> --- a/xen/arch/arm/kernel.c
> +++ b/xen/arch/arm/kernel.c
[...]

> @@ -354,20 +353,28 @@ static int kernel_zimage64_probe(struct kernel_info *info,
>
>       copy_from_paddr(&zimage, addr, sizeof(zimage));
>
> -    if ( zimage.magic0 != ZIMAGE64_MAGIC_V0 &&
> -         zimage.magic1 != ZIMAGE64_MAGIC_V1 )
> +    if ( zimage.magic != ZIMAGE64_MAGIC )
>           return -EINVAL;
>
> -    /* Currently there is no length in the header, so just use the size */
>       start = 0;
> -    end = size;
>
>       /*
> -     * Given the above this check is a bit pointless, but leave it
> -     * here in case someone adds a length field in the future.
> +     * Where image_size is non-zero image_size is little-endian
> +     * and must be respected.
Can you explain what "must be respected" stands for?

>        */
> -    if ( (end - start) > size )
> +    if ( zimage.image_size )
> +        end = zimage.image_size;
> +    else
> +        end = size;
> +
> +    if ( (end - start) > size ) {
> +        if ( zimage.image_size ) {
> +            printk(XENLOG_ERR "Error: Kernel Image size: %lu bytes > bootmodule 
> size: %lu bytes\n",
> +                   zimage.image_size, (uint64_t)size);
> +            printk(XENLOG_ERR "Check the device tree configuration!\n");
This message is not really helpful when using UEFI. In this case, 
multiboot is not used and the kernel image will be loaded by UEFI.
However, the size of the kernel may still mismatch the value in the 
field image_size.
> +        }
>           return -EINVAL;
> +    }
>
>       info->zimage.kernel_addr = addr;
>       info->zimage.len = end - start;
Regards,

--
Julien Grall

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