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From: Marc Zyngier <maz@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Santosh Shukla <sashukla@nvidia.com>,
	Gavin Shan <gshan@redhat.com>,
	kvm@vger.kernel.org, Quentin Perret <qperret@google.com>,
	kernel-team@android.com,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	Vladimir Murzin <vladimir.murzin@arm.com>,
	James Morse <james.morse@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	David Brazdil <dbrazdil@google.com>,
	Will Deacon <will@kernel.org>, Qais Yousef <qais.yousef@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>
Subject: [PATCH 01/12] KVM: arm64: Don't corrupt tpidr_el2 on failed HVC call
Date: Fri, 30 Oct 2020 16:40:06 +0000	[thread overview]
Message-ID: <20201030164017.244287-2-maz@kernel.org> (raw)
In-Reply-To: <20201030164017.244287-1-maz@kernel.org>

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 | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index 47224dc62c51..b11a9d7db677 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -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
-- 
2.28.0


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  reply	other threads:[~2020-10-30 16:42 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-30 16:40 [GIT PULL] KVM/arm64 fixes for 5.10, take #1 Marc Zyngier
2020-10-30 16:40 ` Marc Zyngier [this message]
2020-10-30 16:40 ` [PATCH 02/12] KVM: arm64: Remove leftover kern_hyp_va() in nVHE TLB invalidation Marc Zyngier
2020-10-30 16:40 ` [PATCH 03/12] KVM: arm64: Drop useless PAN setting on host EL1 to EL2 transition Marc Zyngier
2020-10-30 16:40 ` [PATCH 04/12] KVM: arm64: Allocate stage-2 pgd pages with GFP_KERNEL_ACCOUNT Marc Zyngier
2020-10-30 16:40 ` [PATCH 05/12] KVM: arm64: Fix AArch32 handling of DBGD{CCINT, SCRext} and DBGVCR Marc Zyngier
2020-10-30 16:40 ` [PATCH 06/12] KVM: arm64: Fix masks in stage2_pte_cacheable() Marc Zyngier
2020-10-30 16:40 ` [PATCH 07/12] KVM: arm64: Use fallback mapping sizes for contiguous huge page sizes Marc Zyngier
2020-10-30 16:40 ` [PATCH 08/12] KVM: arm64: Force PTE mapping on fault resulting in a device mapping Marc Zyngier
2020-10-30 16:40 ` [PATCH 09/12] KVM: arm64: Factor out is_{vhe,nvhe}_hyp_code() Marc Zyngier
2020-10-30 16:40 ` [PATCH 10/12] arm64: cpufeature: reorder cpus_have_{const, final}_cap() Marc Zyngier
2020-10-30 16:40 ` [PATCH 11/12] arm64: cpufeature: upgrade hyp caps to final Marc Zyngier
2020-10-30 16:40 ` [PATCH 12/12] KVM: arm64: Handle Asymmetric AArch32 systems Marc Zyngier
2020-10-31 14:35 ` [GIT PULL] KVM/arm64 fixes for 5.10, take #1 Paolo Bonzini

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