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

[Coiby Xu]

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@xxxxxxxxxx>
> > ---
> >  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