@@ -730,10 +730,10 @@ static void do_ffa_version(struct arm_smccc_res *res,
hyp_ffa_version = ffa_req_version;
}
- if (hyp_ffa_post_init())
+ if (hyp_ffa_post_init()) {
res->a0 = FFA_RET_NOT_SUPPORTED;
- else {
- has_version_negotiated = true;
+ } else {
+ smp_store_release(&has_version_negotiated, true);
res->a0 = hyp_ffa_version;
}
unlock:
@@ -809,7 +809,8 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
if (!is_ffa_call(func_id))
return false;
- if (!has_version_negotiated && func_id != FFA_VERSION) {
+ if (func_id != FFA_VERSION &&
+ !smp_load_acquire(&has_version_negotiated)) {
ffa_to_smccc_error(&res, FFA_RET_INVALID_PARAMETERS);
goto out_handled;
}
The pKVM FF-A proxy rejects FF-A requests other than FFA_VERSION until version negotiation is complete, which is signalled by setting the global 'has_version_negotiated' variable. To avoid excessive locking, this variable is checked directly from kvm_host_ffa_handler() in response to an FF-A call, but this can race against another CPU performing the negotiation and potentially lead to reading a torn value (incredibly unlikely for a 'bool') or problematic re-ordering of the accesses to 'has_version_negotiated' and 'hyp_ffa_version' whereby a stale version number could be read by __do_ffa_mem_xfer(). Use acquire/release primitives when writing 'has_version_negotiated' with the version lock held and when reading without the lock held. Cc: Sebastian Ene <sebastianene@google.com> Cc: Sudeep Holla <sudeep.holla@arm.com> Cc: Quentin Perret <qperret@google.com> Cc: Oliver Upton <oliver.upton@linux.dev> Cc: Marc Zyngier <maz@kernel.org> Fixes: c9c012625e12 ("KVM: arm64: Trap FFA_VERSION host call in pKVM") Signed-off-by: Will Deacon <will@kernel.org> --- Found by code inspection rather than any real issue in practice. arch/arm64/kvm/hyp/nvhe/ffa.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)