Re: [PATCH v3 3/7] crash_dump: store dm keys in kdump reserved memory

[Coiby Xu]

On Tue, May 21, 2024 at 11:42:52AM +0800, Baoquan He wrote:
> On 04/25/24 at 06:04pm, Coiby Xu wrote:
> > When the kdump kernel image and initrd are loaded, the dm crypts keys
> > will be read from keyring and then stored in kdump reserved memory.
> >
> > Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
> > ---
> >  include/linux/crash_core.h   |  3 ++
> >  include/linux/crash_dump.h   |  2 +
> >  include/linux/kexec.h        |  4 ++
> >  kernel/crash_dump_dm_crypt.c | 87 ++++++++++++++++++++++++++++++++++++
> >  4 files changed, 96 insertions(+)
> >
> > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> > index 98825b7e0ea6..1f3d5a4fa6c1 100644
> > --- a/include/linux/crash_core.h
> > +++ b/include/linux/crash_core.h
> > @@ -37,6 +37,9 @@ static inline void arch_kexec_unprotect_crashkres(void) { }
> >  #ifdef CONFIG_CRASH_DM_CRYPT
> >  int crash_sysfs_dm_crypt_keys_read(char *buf);
> >  int crash_sysfs_dm_crypt_keys_write(const char *buf, size_t count);
> > +int crash_load_dm_crypt_keys(struct kimage *image);
> > +#else
> > +static inline int crash_load_dm_crypt_keys(struct kimage *image) {return 0; }
> >  #endif
> >
> >  #ifndef arch_crash_handle_hotplug_event
> > diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> > index acc55626afdc..dfd8e4fe6129 100644
> > --- a/include/linux/crash_dump.h
> > +++ b/include/linux/crash_dump.h
> > @@ -15,6 +15,8 @@
> >  extern unsigned long long elfcorehdr_addr;
> >  extern unsigned long long elfcorehdr_size;
> >
> > +extern unsigned long long dm_crypt_keys_addr;
> > +
> >  #ifdef CONFIG_CRASH_DUMP
> >  extern int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size);
> >  extern void elfcorehdr_free(unsigned long long addr);
> > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> > index fc1e20d565d5..b6cedce66828 100644
> > --- a/include/linux/kexec.h
> > +++ b/include/linux/kexec.h
> > @@ -368,6 +368,10 @@ struct kimage {
> >  	void *elf_headers;
> >  	unsigned long elf_headers_sz;
> >  	unsigned long elf_load_addr;
> > +
> > +	/* dm crypt keys buffer */
> > +	unsigned long dm_crypt_keys_addr;
> > +	unsigned long dm_crypt_keys_sz;
> >  };
> >
> >  /* kexec interface functions */
> > diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> > index 847499cdcd42..b9997fb53351 100644
> > --- a/kernel/crash_dump_dm_crypt.c
> > +++ b/kernel/crash_dump_dm_crypt.c
> > @@ -1,4 +1,6 @@
> >  // SPDX-License-Identifier: GPL-2.0-only
> > +#include <linux/key.h>
> > +#include <linux/keyctl.h>
> >  #include <keys/user-type.h>
> >  #include <linux/crash_dump.h>
> >
> > @@ -111,3 +113,88 @@ int crash_sysfs_dm_crypt_keys_read(char *buf)
> >  	return sprintf(buf, "%s\n", STATE_STR[state]);
> >  }
> >  EXPORT_SYMBOL(crash_sysfs_dm_crypt_keys_read);
> > +
> > +static int read_key_from_user_keying(struct dm_crypt_key *dm_key)
> > +{
> > +	const struct user_key_payload *ukp;
> > +	struct key *key;
> > +
> > +	pr_debug("Requesting key %s", dm_key->key_desc);
> > +	key = request_key(&key_type_logon, dm_key->key_desc, NULL);
> > +
> > +	if (IS_ERR(key)) {
> > +		pr_warn("No such key %s\n", dm_key->key_desc);
> > +		return PTR_ERR(key);
> > +	}
> > +
> > +	ukp = user_key_payload_locked(key);
> > +	if (!ukp)
> > +		return -EKEYREVOKED;
> > +
> > +	memcpy(dm_key->data, ukp->data, ukp->datalen);
> > +	dm_key->key_size = ukp->datalen;
> > +	pr_debug("Get dm crypt key (size=%u) %s: %8ph\n", dm_key->key_size,
> > +		 dm_key->key_desc, dm_key->data);
> > +	return 0;
> > +}
> > +
> > +static int build_keys_header(void)
> > +{
> > +	int i, r;
> > +
> > +	for (i = 0; i < key_count; i++) {
> > +		r = read_key_from_user_keying(&keys_header->keys[i]);
> > +		if (r != 0) {
> > +			pr_err("Failed to read key %s\n", keys_header->keys[i].key_desc);
> > +			return r;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +int crash_load_dm_crypt_keys(struct kimage *image)
> > +{
> > +	struct kexec_buf kbuf = {
> > +		.image = image,
> > +		.buf_min = 0,
> > +		.buf_max = ULONG_MAX,
> > +		.top_down = false,
> > +		.random = true,
> > +	};
> > +
> > +	int r;
> > +
> > +	if (state == FRESH)
> > +		return 0;
> > +
> > +	if (key_count != keys_header->key_count) {
> > +		pr_err("Only record %u keys (%u in total)\n", key_count,
> > +		       keys_header->key_count);
> > +		return -EINVAL;
> > +	}
> > +
> > +	image->dm_crypt_keys_addr = 0;
> > +	r = build_keys_header();
> > +	if (r)
> > +		return r;
> > +
> > +	kbuf.buffer = keys_header;
> > +	kbuf.bufsz = keys_header_size;
> > +
> > +	kbuf.memsz = kbuf.bufsz;
> > +	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
> > +	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> > +	r = kexec_add_buffer(&kbuf);
> > +	if (r) {
> > +		vfree((void *)kbuf.buffer);
> > +		return r;
> > +	}
> > +	state = LOADED;
> > +	image->dm_crypt_keys_addr = kbuf.mem;
> > +	image->dm_crypt_keys_sz = kbuf.bufsz;
> > +	pr_debug("Loaded dm crypt keys at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> > +		 image->dm_crypt_keys_addr, kbuf.bufsz, kbuf.bufsz);
>
> Please use kexec_dprintk() instead to print debugging message.

Thanks for pointing me to kexec_dprintk! I'll use kexec_dprintk.

> And you don't worry this printing will leak the key position and the
> information?

Thanks for raising this concern! I'll remove the key position info as it
seems kernel dyndbg can be easily enabled.

--
Best regards,
Coiby