linux-kernel - [PATCH v4 10/23] KVM: x86: emulator: em

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Date:   Tue, 25 Oct 2022 15:42:10 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Yang Zhong <yang.zhong@...el.com>,
        linux-kselftest@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Borislav Petkov <bp@...en8.de>,
        Guang Zeng <guang.zeng@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        Wei Wang <wei.w.wang@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>
Subject: [PATCH v4 10/23] KVM: x86: emulator: em_sysexit should update ctxt->mode

SYSEXIT is one of the instructions that can change the
processor mode, thus ctxt->mode should be updated after it.

Note that this is likely a benign bug, because the only problematic
mode change is from 32 bit to 64 bit which can lead to truncation of RIP,
and it is not possible to do with sysexit,
since sysexit running in 32 bit mode will be limited to 32 bit version.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/emulate.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 671f7e5871ff70..e23c984d6aae09 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2525,6 +2525,7 @@ static int em_sysexit(struct x86_emulate_ctxt *ctxt)
 	ops->set_segment(ctxt, ss_sel, &ss, 0, VCPU_SREG_SS);
 
 	ctxt->_eip = rdx;
+	ctxt->mode = usermode;
 	*reg_write(ctxt, VCPU_REGS_RSP) = rcx;
 
 	return X86EMUL_CONTINUE;
-- 
2.34.3