[SRU Focal,Jammy,OEM-6.1,Lunar 0/3] CVE-2023-20588

[Thadeu Lima de Souza Cascardo]

[Impact]
 A division-by-zero error on some AMD processors can potentially return
 speculative data resulting in loss of confidentiality.

[Backport]
There were some minimal conflicts resulting in this being backported before
the SRSO mitigation.

But for 5.4 kernels, the entry code has been changed. And instead of
adopting those changes and introducing new code here, I opted to not touch
that divide error entry code since the added function call added in the
second patch is removed in the third patch. Then, the places where it is
called have moved and I had to manually place them in their equivalent
spots.

[Test case]
The test case here was looking at dmesg for the following line in one
affected part:

"AMD Zen1 DIV0 bug detected. Disable SMT for full protection."

I also tested that an integer division by zero in userspace doesn't cause
any crashes or hiccups in the kernel.

[Potential regression]
Booting on affected parts may be affected. Kernel exit and SVM may be
affected too. Also CPU vulnerability reporting may be affected.

Borislav Petkov (AMD) (3):
  x86/bugs: Increase the x86 bugs vector size to two u32s
  x86/CPU/AMD: Do not leak quotient data after a division by 0
  x86/CPU/AMD: Fix the DIV(0) initial fix attempt

 arch/x86/entry/common.c                  |  1 +
 arch/x86/include/asm/cpufeatures.h       |  4 +++-
 arch/x86/include/asm/processor.h         |  2 ++
 arch/x86/kernel/cpu/amd.c                | 20 ++++++++++++++++++++
 arch/x86/kvm/svm.c                       |  2 ++
 tools/arch/x86/include/asm/cpufeatures.h |  2 +-
 6 files changed, 29 insertions(+), 2 deletions(-)

-- 
2.34.1