On 24/05/18 12:23, Mark Rutland wrote:

On Thu, May 24, 2018 at 12:00:58PM +0100, Mark Rutland wrote:

quoted

On Tue, May 22, 2018 at 04:06:36PM +0100, Marc Zyngier wrote:

quoted

In order for the kernel to protect itself, let's call the SSBD mitigation
implemented by the higher exception level (either hypervisor or firmware)
on each transition between userspace and kernel.

We must take the PSCI conduit into account in order to target the
right exception level, hence the introduction of a runtime patching
callback.

Signed-off-by: Marc Zyngier <redacted>
---
 arch/arm64/kernel/cpu_errata.c | 18 ++++++++++++++++++
 arch/arm64/kernel/entry.S      | 22 ++++++++++++++++++++++
 include/linux/arm-smccc.h      |  5 +++++
 3 files changed, 45 insertions(+)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index a900befadfe8..46b3aafb631a 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c

@@ -232,6 +232,24 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 }
 #endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
 
+#ifdef CONFIG_ARM64_SSBD
+void __init arm64_update_smccc_conduit(struct alt_instr *alt,
+				       __le32 *origptr, __le32 *updptr,
+				       int nr_inst)
+{
+	u32 insn;
+
+	BUG_ON(nr_inst != 1);
+
+	if (psci_ops.conduit == PSCI_CONDUIT_HVC)
+		insn = aarch64_insn_get_hvc_value();
+	else
+		insn = aarch64_insn_get_smc_value();

Shouldn't this also handle the case where there is no conduit?

Due to the config symbol not being defined yet, and various other fixups
in later patches, this is actually benign.

However, if you make this:

	switch (psci_ops.conduit) {
	case PSCI_CONDUIT_NONE:
		return;
	case PSCI_CONDUIT_HVC:
		insn = aarch64_insn_get_hvc_value();
		break;
	case PSCI_CONDUIT_SMC:
		insn = aarch64_insn_get_smc_value();
		break;
	}

... then we won't even bother patching the nop in the default case
regardless, which is nicer, IMO.

Yup, looks better to me too. I'll fold that in.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...