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KVM: arm64: Prevent the host from using an smc with imm16 != 0

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The ARM Service Calling Convention (SMCCC) specifies that the function
identifier and parameters should be passed in registers, leaving the
16-bit immediate field un-handled in pKVM when an SMC instruction is
trapped.
Since the HVC is a private interface between EL2 and the host,
enforce the host kernel running under pKVM to use an immediate value
of 0 only when using SMCs to make it clear for non-compliant software
talking to Trustzone that we only use SMCCC.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260330105441.3226904-1-sebastianene@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Sebastian Ene 2026-03-30 10:54:41 +00:00 committed by Marc Zyngier
parent f338e77383
commit cf6348af64
1 changed files with 7 additions and 0 deletions
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7
arch/arm64/kvm/hyp/nvhe/hyp-main.c
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@ -676,8 +676,14 @@ static void default_host_smc_handler(struct kvm_cpu_context *host_ctxt)
static void handle_host_smc(struct kvm_cpu_context *host_ctxt)
{
DECLARE_REG(u64, func_id, host_ctxt, 0);
u64 esr = read_sysreg_el2(SYS_ESR);
bool handled;
if (esr & ESR_ELx_xVC_IMM_MASK) {
cpu_reg(host_ctxt, 0) = SMCCC_RET_NOT_SUPPORTED;
goto exit_skip_instr;
}
func_id &= ~ARM_SMCCC_CALL_HINTS;
handled = kvm_host_psci_handler(host_ctxt, func_id);
@ -686,6 +692,7 @@ static void handle_host_smc(struct kvm_cpu_context *host_ctxt)
if (!handled)
default_host_smc_handler(host_ctxt);
exit_skip_instr:
/* SMC was trapped, move ELR past the current PC. */
kvm_skip_host_instr();
}