[PATCH 0/4] CRASH_ZEROIZE: Wipe secrets before kdump

I'm using linux on an embedded target in a Hardware Security Module-like
application. One requirement is that I want the system to be able to
quickly erase its memory when it detects physical tampering. I'm
approaching that by using kdump to load into a small payload that
instead of dumping RAM, erases RAM from start to end. However, writing
all of RAM, especially on an embedded target, is rather slow. For this
reason, I propose the mechanism in this patch series:

Add CONFIG_CRASH_ZEROIZE (default off), which when enabled makes various
subsystems handling secret data do a quick, targeted wipe of these
secrets before kdump. This behavior might also be interesting in cases
where you run a normal kdump kernel but you still want to keep things
like fde crypto keys out of these dumps.

CONFIG_CRASH_ZEROIZE is a best effort, defense in depth solution. There
are circumstances, such as when a panic is triggered after memory
corruption, or when a panic interrupts some operation that mutates data
structures under locks, when the kernel cannot safely wipe some memory
areas. The handlers proposed in this series will just print a warning
and skip the affected areas in this case.

This series introduces two handlers as a starting point: One for kernel
keyrings, and one for secretmem. Future places where such handlers could
be added would be for example drivers for crypto accelerators. 

The patch series applies on top of linux-next but should work on 7.0.0,
too. I've tested the patches on a Arduino uno Q (Qualcomm QRB2210)
embedded target.

Jan Sebastian Götte (4):
  of/kexec: fix typo in comment (usable-memory-range)
  kexec: add CRASH_ZEROIZE to wipe secrets before kdump
  mm/secretmem: zeroize secret pages before kdump
  security/keys: zeroize key payloads before kdump

 drivers/of/kexec.c                        |  2 +-
 include/linux/crash_core.h                |  5 +++
 include/linux/key-type.h                  |  9 ++++
 kernel/Kconfig.kexec                      |  8 ++++
 kernel/crash_core.c                       | 18 ++++++++
 mm/secretmem.c                            | 50 +++++++++++++++++++++++
 security/keys/big_key.c                   | 15 +++++++
 security/keys/encrypted-keys/encrypted.c  | 12 ++++++
 security/keys/key.c                       | 44 ++++++++++++++++++++
 security/keys/trusted-keys/trusted_core.c | 14 +++++++
 security/keys/user_defined.c              | 11 +++++
 11 files changed, 187 insertions(+), 1 deletion(-)

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2.53.0