Arm CCA includes "Memory Encryption Contexts" (MEC) which allows the private and shared data accessible to a guest to have different memory encryption keys. Consequently when converting memory to shared, the memory encryption key used to access the physical page will change.
Both the GICv3 ITS driver and the system_cc_shared dma-buf heap currently allocate memory with __GFP_ZERO and then decrypt it. With MEC the zeroing is done with the wrong encryption key and the data visible after decryption may be ciphertext. The RMM is required to scrub the data, but may perform this scrub with a different encryption key to the eventual key that will be used for shared access.
Fix these two sites by avoiding the __GFP_ZERO during the allocation and performing a clear_pages() call after the decryption.
Steven Price (2): irqchip/gic-v3-its: Zero shared pages after conversion dma-buf: heaps: Zero system shared heap pages after conversion
drivers/dma-buf/heaps/system_heap.c | 14 +++++++++++--- drivers/irqchip/irq-gic-v3-its.c | 7 ++++++- 2 files changed, 17 insertions(+), 4 deletions(-)