Add a microcode disable chicken bit

From: Borislav Petkov <[email protected]>

Hi,

so there are situations where we want to be able to turn off the microcode loader, especially the early part, to rule out any possible influence from it accessing ucode blobs early from the initrd and/or having other effects on the system.

These patches add a "dis_ucode_ldr" (when early loading is not built in, use with the prefix, i.e. "microcode.dis_ucode_ldr") which enables that.

For that we needed a fairly self-contained cmdline parsing function which we almost copied from arch/x86/boot/cmdline.c

The dancing in check_loader_disabled_*() variants is needed because on 32-bit we're running before paging is enabled and there we need to deal with physical addresses.

As always, any comments and suggestions are appreciated.

Thanks.

Borislav Petkov (2):
x86: Carve out cmdline parsing function
x86, microcode: Add a disable chicken bit

 arch/x86/include/asm/cmdline.h             |  6 +++
 arch/x86/include/asm/microcode.h           |  1 +
 arch/x86/kernel/cpu/microcode/core.c       |  6 +++
 arch/x86/kernel/cpu/microcode/core_early.c | 37 +++++++++++++
 arch/x86/lib/Makefile                      |  2 +-
 arch/x86/lib/cmdline.c                     | 84 ++++++++++++++++++++++++++++++
 6 files changed, 135 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/include/asm/cmdline.h
 create mode 100644 arch/x86/lib/cmdline.c

1.9.0