[PATCH v6 6/7] x86/crash: pass dm crypt keys to kdump kernel

[Coiby Xu]

On Wed, Dec 11, 2024 at 08:55:52PM +0800, Baoquan He wrote:
>On 10/29/24 at 01:52pm, Coiby Xu wrote:
>> 1st kernel will build up the kernel command parameter dmcryptkeys as
>> similar to elfcorehdr to pass the memory address of the stored info of
>> dm crypt key to kdump kernel.
>>
>> Signed-off-by: Coiby Xu <coxu at redhat.com>
>> ---
>>  arch/x86/kernel/crash.c           | 20 ++++++++++++++++++--
>>  arch/x86/kernel/kexec-bzimage64.c |  7 +++++++
>>  2 files changed, 25 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 340af8155658..99d50c31db02 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -278,6 +278,7 @@ static int memmap_exclude_ranges(struct kimage *image, struct crash_mem *cmem,
>>  				 unsigned long long mend)
>>  {
>>  	unsigned long start, end;
>> +	int ret;
>>
>>  	cmem->ranges[0].start = mstart;
>>  	cmem->ranges[0].end = mend;
>> @@ -286,22 +287,37 @@ static int memmap_exclude_ranges(struct kimage *image, struct crash_mem *cmem,
>>  	/* Exclude elf header region */
>>  	start = image->elf_load_addr;
>>  	end = start + image->elf_headers_sz - 1;
>> -	return crash_exclude_mem_range(cmem, start, end);
>> +	ret = crash_exclude_mem_range(cmem, start, end);
>> +
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* Exclude dm crypt keys region */
>> +	if (image->dm_crypt_keys_addr) {
>> +		start = image->dm_crypt_keys_addr;
>> +		end = start + image->dm_crypt_keys_sz - 1;
>> +		return crash_exclude_mem_range(cmem, start, end);
>> +	}
>> +
>> +	return ret;
>>  }
>>
>>  /* Prepare memory map for crash dump kernel */
>>  int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>>  {
>> +	unsigned int max_nr_ranges = 3;
>
>Define a macro and add code comment to explain why this value is taken?

Good suggestion! While drafting the reason for max_nr_ranges=3, I
realize max_nr_ranges=2 is sufficient. I also notice the fill_up_crash_elf_data
function in the same source file has similar comment. So next version
I'll add the following change,


      int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
      {
     +       unsigned int nr_ranges = 0;
             int i, ret = 0;
             unsigned long flags;
             struct e820_entry ei;
             struct crash_memmap_data cmd;
             struct crash_mem *cmem;
      
     -       cmem = vzalloc(struct_size(cmem, ranges, 1));
     +       /*
     +        * Using random kexec_buf for passing dm crypt keys may cause a range
     +        * split. So use two slots here.
     +        */
     +       nr_ranges = 2;
     +       cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
             if (!cmem)
                     return -ENOMEM;
      
     +       cmem->max_nr_ranges = nr_ranges;
     +       cmem->nr_ranges = 0;

>
>>  	int i, ret = 0;
>>  	unsigned long flags;
>>  	struct e820_entry ei;
>>  	struct crash_memmap_data cmd;
>>  	struct crash_mem *cmem;
>>
>> -	cmem = vzalloc(struct_size(cmem, ranges, 1));
>> +	cmem = vzalloc(struct_size(cmem, ranges, max_nr_ranges));
>>  	if (!cmem)
>>  		return -ENOMEM;
>>
>> +	cmem->max_nr_ranges = max_nr_ranges;
>> +
>>  	memset(&cmd, 0, sizeof(struct crash_memmap_data));
>>  	cmd.params = params;
>>
>> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
>> index 68530fad05f7..9c94428927bd 100644
>> --- a/arch/x86/kernel/kexec-bzimage64.c
>> +++ b/arch/x86/kernel/kexec-bzimage64.c
>> @@ -76,6 +76,10 @@ static int setup_cmdline(struct kimage *image, struct boot_params *params,
>>  	if (image->type == KEXEC_TYPE_CRASH) {
>>  		len = sprintf(cmdline_ptr,
>>  			"elfcorehdr=0x%lx ", image->elf_load_addr);
>> +
>> +		if (image->dm_crypt_keys_addr != 0)
>> +			len += sprintf(cmdline_ptr + len,
>> +					"dmcryptkeys=0x%lx ", image->dm_crypt_keys_addr);
>>  	}
>>  	memcpy(cmdline_ptr + len, cmdline, cmdline_len);
>>  	cmdline_len += len;
>> @@ -441,6 +445,9 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
>>  		ret = crash_load_segments(image);
>>  		if (ret)
>>  			return ERR_PTR(ret);
>> +		ret = crash_load_dm_crypt_keys(image);
>> +		if (ret)
>> +			pr_debug("Either no dm crypt key or error to retrieve the dm crypt key\n");
>
>If it's error, do we need change ti to pr_debug?

Thanks for raising the concern! I think it's OK to let
crash_load_dm_crypt_keys fail since disk encryption may not be used for
kdump, thus pr_debug is sufficient. Or have I misunderstood your comment?

>>  	}
>>  #endif
>>
>> --
>> 2.47.0
>>
>

-- 
Best regards,
Coiby