linux-kernel - Re: [PATCH v12 15/16] arm64: kexec_file: add kernel signature verification support

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Message-ID: <d3704585-9404-a56b-883a-30c123084ada@arm.com>
Date:   Thu, 26 Jul 2018 14:39:25 +0100
From:   James Morse <james.morse@....com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     catalin.marinas@....com, will.deacon@....com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, dyoung@...hat.com, bhe@...hat.com,
        arnd@...db.de, schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        ard.biesheuvel@...aro.org, bhsharma@...hat.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 15/16] arm64: kexec_file: add kernel signature
 verification support

Hi Akashi,

On 24/07/18 07:57, AKASHI Takahiro wrote:
> With this patch, kernel verification can be done without IMA security
> subsystem enabled. Turn on CONFIG_KEXEC_VERIFY_SIG instead.
> 
> On x86, a signature is embedded into a PE file (Microsoft's format) header
> of binary. Since arm64's "Image" can also be seen as a PE file as far as
> CONFIG_EFI is enabled, we adopt this format for kernel signing.
> 
> You can create a signed kernel image with:
>     $ sbsign --key ${KEY} --cert ${CERT} Image

Reviewed-by: James Morse <james.morse@....com>


> diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> index d64f5e9f9d22..578d358632d0 100644
> --- a/arch/arm64/kernel/kexec_image.c
> +++ b/arch/arm64/kernel/kexec_image.c
> @@ -102,7 +106,18 @@ static void *image_load(struct kimage *image,
>  	return ERR_PTR(ret);
>  }
>  
> +#ifdef CONFIG_KEXEC_IMAGE_VERIFY_SIG
> +static int image_verify_sig(const char *kernel, unsigned long kernel_len)
> +{
> +	return verify_pefile_signature(kernel, kernel_len, NULL,
> +				       VERIFYING_KEXEC_PE_SIGNATURE);
> +}
> +#endif

This is identical to x86's PE image verification helper. We can clean this up
later by providing some kexec_image_verify_pe() in the core kexec_file code. Its
not worth doing now.


>  const struct kexec_file_ops kexec_image_ops = {
>  	.probe = image_probe,
>  	.load = image_load,
> +#ifdef CONFIG_KEXEC_IMAGE_VERIFY_SIG
> +	.verify_sig = image_verify_sig,
> +#endif
>  };


Thanks,

James