linux-kernel - Re: [PATCH v4 2/7] crash_dump: make dm crypt keys persist for the kdump kernel

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Message-ID: <epa3mtnac3ekyoq7zykyjnhu3i27mivbtlkss6mbjyaa3kmhof@qwbfshfbtei4>
Date: Fri, 7 Jun 2024 20:27:07 +0800
From: Coiby Xu <coxu@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: kexec@...ts.infradead.org, Ondrej Kozina <okozina@...hat.com>, 
	Milan Broz <gmazyland@...il.com>, Thomas Staudt <tstaudt@...ibm.com>, 
	Daniel P . Berrangé <berrange@...hat.com>, Kairui Song <ryncsn@...il.com>, 
	Jan Pazdziora <jpazdziora@...hat.com>, Pingfan Liu <kernelfans@...il.com>, 
	Dave Young <dyoung@...hat.com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Dave Hansen <dave.hansen@...el.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, 
	Vivek Goyal <vgoyal@...hat.com>, Kees Cook <keescook@...omium.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, 
	"open list:KERNEL HARDENING (not covered by other areas):Keyword:b__counted_byb" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v4 2/7] crash_dump: make dm crypt keys persist for the
 kdump kernel

On Tue, Jun 04, 2024 at 04:51:03PM +0800, Baoquan He wrote:
>Hi Coiby,

Hi Baoquan,

>
>On 05/23/24 at 01:04pm, Coiby Xu wrote:
>> A sysfs /sys/kernel/crash_dm_crypt_keys is provided for user space to make
>> the dm crypt keys persist for the kdump kernel. User space can send the
>> following commands,
>> - "init KEY_NUM"
>>   Initialize needed structures
>> - "record KEY_DESC"
>>   Record a key description. The key must be a logon key.
>>
>> User space can also read this API to learn about current state.
>
>>From the subject, can I think the luks keys will persist forever? or
>only for a while? 

Yes, you are right. The keys need to stay in kdump reserved memory.

> If need and can only keep it for a while, can you
>mention it and tell why and how it will be used. Because you add a lot
>of codes, but only simply mention the sysfs, that doesn't make sense.

Thanks for raising the concern! I've added
Documentation/ABI/testing/crash_dm_crypt_keys and copy some text in the
cover letter to this patch in v5. 

>
>>
>> Signed-off-by: Coiby Xu <coxu@...hat.com>
>> ---
>>  include/linux/crash_core.h   |   5 +-
>>  kernel/Kconfig.kexec         |   8 +++
>>  kernel/Makefile              |   1 +
>>  kernel/crash_dump_dm_crypt.c | 113 +++++++++++++++++++++++++++++++++++
>>  kernel/ksysfs.c              |  22 +++++++
>>  5 files changed, 148 insertions(+), 1 deletion(-)
>>  create mode 100644 kernel/crash_dump_dm_crypt.c
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index 44305336314e..6bff1c24efa3 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -34,7 +34,10 @@ static inline void arch_kexec_protect_crashkres(void) { }
>>  static inline void arch_kexec_unprotect_crashkres(void) { }
>>  #endif
[...]
>> +static int init(const char *buf)
>              ~~~~ A more interesting name with more description?

Thanks for the suggestion! I've added some comments for this function
in v5. But I can't come up with a better name after looking at current
kernel code. You are welcome to suggest any better name:)

>> +static int process_cmd(const char *buf, size_t count)
>                                                  ~~~~
>If nobody use the count, why do you add it?

Good catch! Yes, this is no need to use count in v4. But v5 now needs it to avoid
buffer overflow.

-- 
Best regards,
Coiby