linux-kernel - Re: [PATCH v5 3/3] arm64: kexec_file: use more system keyrings to verify kernel image signature

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Message-ID: <20220411085938.GA163591@kunlun.suse.cz>
Date:   Mon, 11 Apr 2022 10:59:38 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Coiby Xu <coxu@...hat.com>
Cc:     kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Catalin Marinas <catalin.marinas@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/3] arm64: kexec_file: use more system keyrings to
 verify kernel image signature

On Fri, Apr 01, 2022 at 09:31:18AM +0800, Coiby Xu wrote:
> Currently, a problem faced by arm64 is if a kernel image is signed by a
> MOK key, loading it via the kexec_file_load() system call would be
> rejected with the error "Lockdown: kexec: kexec of unsigned images is
> restricted; see man kernel_lockdown.7".

This is because image_verify_sig uses only the primary keyring that
contains only kernel built-in keys to verify the kexec image.

> This patch allows to verify arm64 kernel image signature using not only
> .builtin_trusted_keys but also .platform and .secondary_trusted_key
> keyring.
> 
> Acked-by: Will Deacon <will@...nel.org>
> Signed-off-by: Coiby Xu <coxu@...hat.com>
> ---
>  arch/arm64/kernel/kexec_image.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> index 9ec34690e255..51af1c22d6da 100644
> --- a/arch/arm64/kernel/kexec_image.c
> +++ b/arch/arm64/kernel/kexec_image.c
> @@ -14,7 +14,6 @@
>  #include <linux/kexec.h>
>  #include <linux/pe.h>
>  #include <linux/string.h>
> -#include <linux/verification.h>
>  #include <asm/byteorder.h>
>  #include <asm/cpufeature.h>
>  #include <asm/image.h>
> @@ -133,8 +132,7 @@ static void *image_load(struct kimage *image,
>  #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);
> +	return kexec_kernel_verify_pe_sig(kernel, kernel_len);
>  }
>  #endif

You can eliminate image_verify_sig here aswell and directly assign
kexec_kernel_verify_pe_sig to fops.

Thanks

Michal