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FROMGIT: KVM: arm64: Use acquire/release to communicate FF-A version negotiation

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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: c9c012625e ("KVM: arm64: Trap FFA_VERSION host call in pKVM")
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20250407152755.1041-1-will@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
(cherry picked from commit a344e258acb0a7f0e7ed10a795c52d1baf705164
 kvmarm/fixes)
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I5ce2a3ea56eff9fb2cc30026a0e46db1ea4d87fd
This commit is contained in:
Will Deacon
2025-04-07 16:27:55 +01:00
committed by Will Deacon
parent 98d798dc6b
commit 65346f1d95
1 changed files with 5 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/arm64/kvm/hyp/nvhe/ffa.c
+5 -4
View File
@@ -751,10 +751,10 @@ 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:
@@ -833,7 +833,8 @@ 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;
}