linux-kernel - [PATCH v3 12/12] KVM: arm64: BTI: Reset BTYPE when skipping emulated instructions

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Message-Id: <1571419545-20401-13-git-send-email-Dave.Martin@arm.com>
Date:   Fri, 18 Oct 2019 18:25:45 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Jones <drjones@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Sudakshina Das <sudi.das@....com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v3 12/12] KVM: arm64: BTI: Reset BTYPE when skipping emulated instructions

Since normal execution of any non-branch instruction resets the
PSTATE BTYPE field to 0, so do the same thing when emulating a
trapped instruction.

Branches don't trap directly, so we should never need to assign a
non-zero value to BTYPE here.

Signed-off-by: Dave Martin <Dave.Martin@....com>

---

Changes since v2:

 * Drop (u64) case when masking out PSR_BTYPE_MASK in
   arm64_skip_faulting_instruction().

   PSTATE may grow, but we should address this more generally rather
   than with point hacks.

 * Add { } around if () clause that was unbalanced by the previous
   patch.
---
 arch/arm64/include/asm/kvm_emulate.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index d69c1ef..f41bfdee 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -450,10 +450,12 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
 
 static inline void kvm_skip_instr(struct kvm_vcpu *vcpu, bool is_wide_instr)
 {
-	if (vcpu_mode_is_32bit(vcpu))
+	if (vcpu_mode_is_32bit(vcpu)) {
 		kvm_skip_instr32(vcpu, is_wide_instr);
-	else
+	} else {
 		*vcpu_pc(vcpu) += 4;
+		*vcpu_cpsr(vcpu) &= ~PSR_BTYPE_MASK;
+	}
 
 	/* advance the singlestep state machine */
 	*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
-- 
2.1.4