KVM: arm64: Don't corrupt tpidr_el2 on failed HVC call (28e81c62) · Commits · 戴 / test

The hyp-init code starts by stashing a register in TPIDR_EL2 in in order to free a register. This happens no matter if the HVC call is legal or not. Although nothing wrong seems to come out of it, it feels odd to alter the EL2 state for something that eventually returns an error. Instead, use the fact that we know exactly which bits of the __kvm_hyp_init call are non-zero to perform the check with a series of EOR/ROR instructions, combined with a build-time check that the value is the one we expect. Signed-off-by:

Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20201026095116.72051-2-maz@kernel.org

arch/arm64/kvm/hyp/nvhe/hyp-init.S

+16 −7

Original line number	Diff line number	Diff line
		@@ -57,16 +57,25 @@ __do_hyp_init:
		cmp x0, #HVC_STUB_HCALL_NR
		b.lo __kvm_handle_stub_hvc

		/* Set tpidr_el2 for use by HYP to free a register */
		msr tpidr_el2, x2

		mov x2, #KVM_HOST_SMCCC_FUNC(__kvm_hyp_init)
		cmp x0, x2
		b.eq 1f
		// We only actively check bits [24:31], and everything
		// else has to be zero, which we check at build time.
		#if (KVM_HOST_SMCCC_FUNC(__kvm_hyp_init) & 0xFFFFFFFF00FFFFFF)
		#error Unexpected __KVM_HOST_SMCCC_FUNC___kvm_hyp_init value
		#endif

		ror x0, x0, #24
		eor x0, x0, #((KVM_HOST_SMCCC_FUNC(__kvm_hyp_init) >> 24) & 0xF)
		ror x0, x0, #4
		eor x0, x0, #((KVM_HOST_SMCCC_FUNC(__kvm_hyp_init) >> 28) & 0xF)
		cbz x0, 1f
		mov x0, #SMCCC_RET_NOT_SUPPORTED
		eret

		1: phys_to_ttbr x0, x1
		1:
		/* Set tpidr_el2 for use by HYP to free a register */
		msr tpidr_el2, x2

		phys_to_ttbr x0, x1
		alternative_if ARM64_HAS_CNP
		orr x0, x0, #TTBR_CNP_BIT
		alternative_else_nop_endif

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