KVM: arm64: Fix clobbered ELR in sync abort
When the hypervisor receives a SError or synchronous exception (EL2h)
while running with the __kvm_hyp_vector and if ELR_EL2 doesn't point to
an extable entry, it panics indirectly by overwriting ELR with the
address of a panic handler in order for the ASM routine it returns to to
ERET into the handler. This is done (instead of a simple function call)
to ensure that the panic handler runs with the SPSel that was in use
when the exception was triggered, necessary to support features such as
the shadow call stack.
However, this clobbers ELR_EL2 for the handler itself. As a result,
hyp_panic(), when retrieving what it believes to be the PC where the
exception happened, actually ends up reading the address of the panic
handler that called it! This results in an erroneous and confusing panic
message where the source of any synchronous exception (e.g. BUG() or
KCFI) appears to be __hyp_panic_with_context, making it hard to locate
the actual BRK instruction.
Therefore, store the original ELR_EL2 in a per-CPU struct and point the
sysreg to a routine that first restores it to its previous value before
running __hyp_panic_with_context.
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
3 files changed
