[Xen-devel] update on the status of SP2 mitigations for Xen on Arm

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Hi all,

This is the latest status of the SP2 mitigations for Xen on Arm. Please
note that arm32 and arm64 require different mitigations.

I have just backported the arm32 mitigation to 4.10, 4.9, 4.8 and 4.7:

- 4.10
bbd093c xen/arm32: entry: Document the purpose of r11 in the traps handler
a69a8b5 xen/arm32: Invalidate icache on guest exist for Cortex-A15
f167ebf xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12
c4c0187 xen/arm32: Add skeleton to harden branch predictor aliasing attacks
19ad8a7 xen/arm32: entry: Add missing trap_reset entry
3caf32c xen/arm32: Add missing MIDR values for Cortex-A17 and A12
df7be94 xen/arm32: entry: Consolidate DEFINE_TRAP_ENTRY_* macros

- 4.9
4d01dbc xen/arm32: entry: Document the purpose of r11 in the traps handler
22379b6 xen/arm32: Invalidate icache on guest exist for Cortex-A15
6e13ad7 xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12
0d32237 xen/arm32: Add skeleton to harden branch predictor aliasing attacks
4ba59bd xen/arm32: entry: Add missing trap_reset entry
2997c5e xen/arm32: Add missing MIDR values for Cortex-A17 and A12
751c879 xen/arm32: entry: Consolidate DEFINE_TRAP_ENTRY_* macros

- 4.8
11875b7 xen/arm32: entry: Document the purpose of r11 in the traps handler
1105f3a xen/arm32: Invalidate icache on guest exist for Cortex-A15
754345c xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12
7336d0d xen/arm32: Add skeleton to harden branch predictor aliasing attacks
cf95bba xen/arm32: entry: Add missing trap_reset entry
a586cbd xen/arm32: Add missing MIDR values for Cortex-A17 and A12
6082e3b xen/arm32: entry: Consolidate DEFINE_TRAP_ENTRY_* macros

- 4.7
f50ea84 xen/arm32: entry: Document the purpose of r11 in the traps handler
de3bdaa xen/arm32: Invalidate icache on guest exist for Cortex-A15
766990b xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12
4ac0229 xen/arm32: Add skeleton to harden branch predictor aliasing attacks
bafd63f xen/arm32: entry: Add missing trap_reset entry
d5bb425 xen/arm32: Add missing MIDR values for Cortex-A17 and A12
003ec3e xen/arm32: entry: Consolidate DEFINE_TRAP_ENTRY_* macros


The arm64 backports have been in the staging trees for a while, see:
https://marc.info/?l=xen-devel&m=151690105623579

Julien posted another series to improve the SP2 mitigation for arm64:
https://marc.info/?l=xen-devel&m=151783688420038
It is not yet reviewed. This second series is highly desirable, as it
uses better firmware interfaces for the mitigation.

At present, Xen is using a PSCI get_version call (it is a call to the
PSCI firmware) for the mitigation. It relies on the firmware cleaning
the branch predictor cache in the implementation of the get_version
call. However, it appers that get_version doesn't actually do the
expected task on most arm64 platforms. Hence, the need for a new series
and a better firmware call. Julien, feel free to add more details here.

Cheers,

Stefano

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