Re: Re: [PATCH v2 2/5] crash_dump: save the dm crypt key temporarily

[Coiby Xu]

On Tue, Jan 16, 2024 at 11:40:53AM +0100, Ondrej Kozina wrote:
> On 10/01/2024 08:15, Coiby Xu wrote:
> > User space is supposed to write the key description to
> > /sys/kernel/crash_dm_crypt_key so the kernel will read the key and save
> > a temporary copy for later user. User space has 2 minutes at maximum to
> > load the kdump initrd before the key gets wiped. And after kdump
> > retrieves the key, the key will be wiped immediately.
> >
> > Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
> > ---
> >  include/linux/crash_core.h   |   7 +-
> >  include/linux/kexec.h        |   4 ++
> >  kernel/Makefile              |   2 +-
> >  kernel/crash_dump_dm_crypt.c | 121 +++++++++++++++++++++++++++++++++++
> >  kernel/ksysfs.c              |  23 ++++++-
> >  5 files changed, 153 insertions(+), 4 deletions(-)
> >  create mode 100644 kernel/crash_dump_dm_crypt.c
> >
> > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> > index 5126a4fecb44..7078eda6418d 100644
> > --- a/include/linux/crash_core.h
> > +++ b/include/linux/crash_core.h
> > @@ -125,6 +125,12 @@ static inline void __init reserve_crashkernel_generic(char *cmdline,
> >  {}
> >  #endif
> > +struct kimage;
> > +
> > +int crash_sysfs_dm_crypt_key_write(const char *key_des, size_t count);
> > +int crash_pass_temp_dm_crypt_key(void **addr, unsigned long *sz);
> > +int crash_load_dm_crypt_key(struct kimage *image);
> > +
> >  /* Alignment required for elf header segment */
> >  #define ELF_CORE_HEADER_ALIGN   4096
> > @@ -140,7 +146,6 @@ extern int crash_exclude_mem_range(struct crash_mem *mem,
> >  extern int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> >  				       void **addr, unsigned long *sz);
> > -struct kimage;
> >  struct kexec_segment;
> >  #define KEXEC_CRASH_HP_NONE			0
> > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> > index 6f4626490ebf..bf7ab1e927ef 100644
> > --- a/include/linux/kexec.h
> > +++ b/include/linux/kexec.h
> > @@ -366,6 +366,10 @@ struct kimage {
> >  	void *elf_headers;
> >  	unsigned long elf_headers_sz;
> >  	unsigned long elf_load_addr;
> > +
> > +	/* dm crypt key buffer */
> > +	unsigned long dm_crypt_key_addr;
> > +	unsigned long dm_crypt_key_sz;
> >  };
> >  /* kexec interface functions */
> > diff --git a/kernel/Makefile b/kernel/Makefile
> > index 3947122d618b..48859bf63db5 100644
> > --- a/kernel/Makefile
> > +++ b/kernel/Makefile
> > @@ -119,7 +119,7 @@ obj-$(CONFIG_PERF_EVENTS) += events/
> >  obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
> >  obj-$(CONFIG_PADATA) += padata.o
> > -obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
> > +obj-$(CONFIG_CRASH_DUMP) += crash_dump.o crash_dump_dm_crypt.o
> >  obj-$(CONFIG_JUMP_LABEL) += jump_label.o
> >  obj-$(CONFIG_CONTEXT_TRACKING) += context_tracking.o
> >  obj-$(CONFIG_TORTURE_TEST) += torture.o
> > diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> > new file mode 100644
> > index 000000000000..3a0b0b773598
> > --- /dev/null
> > +++ b/kernel/crash_dump_dm_crypt.c
> > @@ -0,0 +1,121 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +#include <keys/user-type.h>
> > +#include <linux/crash_dump.h>
> > +
> > +static u8 *dm_crypt_key;
> > +static unsigned int dm_crypt_key_size;
> > +
> > +void wipe_dm_crypt_key(void)
> > +{
> > +	if (dm_crypt_key) {
> > +		memset(dm_crypt_key, 0, dm_crypt_key_size * sizeof(u8));
> > +		kfree(dm_crypt_key);
> > +		dm_crypt_key = NULL;
> > +	}
> > +}
> > +
> > +static void _wipe_dm_crypt_key(struct work_struct *dummy)
> > +{
> > +	wipe_dm_crypt_key();
> > +}
> > +
> > +static DECLARE_DELAYED_WORK(wipe_dm_crypt_key_work, _wipe_dm_crypt_key);
> > +
> > +static unsigned __read_mostly wipe_key_delay = 120; /* 2 mins */
> > +
> > +static int crash_save_temp_dm_crypt_key(const char *key_desc, size_t count)
> > +{
> > +	const struct user_key_payload *ukp;
> > +	struct key *key;
> > +
> > +	if (dm_crypt_key) {
> > +		memset(dm_crypt_key, 0, dm_crypt_key_size * sizeof(u8));
> > +		kfree(dm_crypt_key);
> > +	}
> > +
> > +	pr_debug("Requesting key %s", key_desc);
> > +	key = request_key(&key_type_user, key_desc, NULL);
>
> If we don't read the key copy form userspace (my reply to top level 
> message) you could use key_type_logon here.

I'll use key_type_logon, thanks!

--
Best regards,
Coiby