linux-kernel - Re: [PATCH v4 1/3] kexec: clean up arch_kexec_kernel_verify

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Message-ID: <20220322025912.r2ahc2ztx3npt7av@Rk>
Date:   Tue, 22 Mar 2022 10:59:12 +0800
From:   Coiby Xu <coxu@...hat.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        Dave Young <dyoung@...hat.com>, Will Deacon <will@...nel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] kexec: clean up arch_kexec_kernel_verify_sig

On Mon, Mar 21, 2022 at 12:21:33PM +0800, Baoquan He wrote:
>On 03/18/22 at 05:40pm, Coiby Xu wrote:
>> Commit 9ec4ecef0af7 ("kexec_file,x86,powerpc: factor out kexec_file_ops
>> functions") allows implementing the arch-specific implementation of kernel
>> image verification in kexec_file_ops->verify_sig. Currently, there is no
>
>Looking back at the old commit 9ec4ecef0af7, it mistakenly added a
>generic arch_kexec_kernel_verify_sig() which is marked as __weak,
>and expects any architecture will add a arch specified version if needed.
>In fact those arch specified difference has been removed by wrapping
>them into each architecture's own struct kexec_file_ops methods. Means
>in the commit, the generic arch_kexec_kernel_verify_sig() is unnecessary
>at all.

Thanks for looking at commit 9ec4ecef0af7 for me!

Although commit 9ec4ecef0af7 added some code in arch_kexec_kernel_verify_sig
so kexec_file_ops->verify_sig can be called, this commit doesn't add __weak
arch_kexec_kernel_verify_sig itself. And kexec_file_ops isn't supposed
to replace arch-specific implementation using __weak considering s390 and x86
still make use of __weak to implement its own version of 
arch_kexec_apply_relocations_add. How about the commit message as
follows?

   Currently this no arch-specific implementation of
   arch_kexec_kernel_verify_sig. Even if we want to add an implementation
   for an architecture in the future, we can simply use "(struct
   kexec_file_ops*)->verify_sig". So clean it up.
>
>Now, you clean up that uncessary function with code change.
>
>I think description telling above analysis could be clearer.
>
>> arch-specific implementation of arch_kexec_kernel_verify_sig. So clean it
>> up.
>>
>> Suggested-by: Eric W. Biederman <ebiederm@...ssion.com>
>> Signed-off-by: Coiby Xu <coxu@...hat.com>
>> ---
>>  include/linux/kexec.h |  4 ----
>>  kernel/kexec_file.c   | 34 +++++++++++++---------------------
>>  2 files changed, 13 insertions(+), 25 deletions(-)
>>
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 0c994ae37729..755fed183224 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -196,10 +196,6 @@ int arch_kexec_apply_relocations(struct purgatory_info *pi,
>>  				 const Elf_Shdr *relsec,
>>  				 const Elf_Shdr *symtab);
>>  int arch_kimage_file_post_load_cleanup(struct kimage *image);
>> -#ifdef CONFIG_KEXEC_SIG
>> -int arch_kexec_kernel_verify_sig(struct kimage *image, void *buf,
>> -				 unsigned long buf_len);
>> -#endif
>>  int arch_kexec_locate_mem_hole(struct kexec_buf *kbuf);
>>
>>  extern int kexec_add_buffer(struct kexec_buf *kbuf);
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index 8347fc158d2b..3720435807eb 100644
>> --- a/kernel/kexec_file.c
>> +++ b/kernel/kexec_file.c
>> @@ -89,25 +89,6 @@ int __weak arch_kimage_file_post_load_cleanup(struct kimage *image)
>>  	return kexec_image_post_load_cleanup_default(image);
>>  }
>>
>> -#ifdef CONFIG_KEXEC_SIG
>> -static int kexec_image_verify_sig_default(struct kimage *image, void *buf,
>> -					  unsigned long buf_len)
>> -{
>> -	if (!image->fops || !image->fops->verify_sig) {
>> -		pr_debug("kernel loader does not support signature verification.\n");
>> -		return -EKEYREJECTED;
>> -	}
>> -
>> -	return image->fops->verify_sig(buf, buf_len);
>> -}
>> -
>> -int __weak arch_kexec_kernel_verify_sig(struct kimage *image, void *buf,
>> -					unsigned long buf_len)
>> -{
>> -	return kexec_image_verify_sig_default(image, buf, buf_len);
>> -}
>> -#endif
>> -
>>  /*
>>   * arch_kexec_apply_relocations_add - apply relocations of type RELA
>>   * @pi:		Purgatory to be relocated.
>> @@ -184,13 +165,24 @@ void kimage_file_post_load_cleanup(struct kimage *image)
>>  }
>>
>>  #ifdef CONFIG_KEXEC_SIG
>> +static int kexec_image_verify_sig(struct kimage *image, void *buf,
>> +		unsigned long buf_len)
>> +{
>> +	if (!image->fops || !image->fops->verify_sig) {
>> +		pr_debug("kernel loader does not support signature verification.\n");
>> +		return -EKEYREJECTED;
>> +	}
>> +
>> +	return image->fops->verify_sig(buf, buf_len);
>> +}
>> +
>>  static int
>>  kimage_validate_signature(struct kimage *image)
>>  {
>>  	int ret;
>>
>> -	ret = arch_kexec_kernel_verify_sig(image, image->kernel_buf,
>> -					   image->kernel_buf_len);
>> +	ret = kexec_image_verify_sig(image, image->kernel_buf,
>> +			image->kernel_buf_len);
>>  	if (ret) {
>>
>>  		if (IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) {
>> --
>> 2.34.1
>>
>

-- 
Best regards,
Coiby