linux-kernel - [PATCH 5.11 296/306] KVM: arm64: Avoid corrupting vCPU context register in guest exit

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Date:   Mon, 15 Mar 2021 15:24:21 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Andrew Scull <ascull@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Will Deacon <will@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.11 296/306] KVM: arm64: Avoid corrupting vCPU context register in guest exit

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Will Deacon <will@...nel.org>

commit 31948332d5fa392ad933f4a6a10026850649ed76 upstream.

Commit 7db21530479f ("KVM: arm64: Restore hyp when panicking in guest
context") tracks the currently running vCPU, clearing the pointer to
NULL on exit from a guest.

Unfortunately, the use of 'set_loaded_vcpu' clobbers x1 to point at the
kvm_hyp_ctxt instead of the vCPU context, causing the subsequent RAS
code to go off into the weeds when it saves the DISR assuming that the
CPU context is embedded in a struct vCPU.

Leave x1 alone and use x3 as a temporary register instead when clearing
the vCPU on the guest exit path.

Cc: Marc Zyngier <maz@...nel.org>
Cc: Andrew Scull <ascull@...gle.com>
Cc: <stable@...r.kernel.org>
Fixes: 7db21530479f ("KVM: arm64: Restore hyp when panicking in guest context")
Suggested-by: Quentin Perret <qperret@...gle.com>
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Link: https://lore.kernel.org/r/20210226181211.14542-1-will@kernel.org
Message-Id: <20210305185254.3730990-3-maz@...nel.org>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/kvm/hyp/entry.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -146,7 +146,7 @@ SYM_INNER_LABEL(__guest_exit, SYM_L_GLOB
 	// Now restore the hyp regs
 	restore_callee_saved_regs x2
 
-	set_loaded_vcpu xzr, x1, x2
+	set_loaded_vcpu xzr, x2, x3
 
 alternative_if ARM64_HAS_RAS_EXTN
 	// If we have the RAS extensions we can consume a pending error