linux-kernel - [PATCH v2 2/8] KVM: x86: Use a new flag for branch instructions

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Message-Id: <20230718131844.5706-3-guang.zeng@intel.com>
Date:   Tue, 18 Jul 2023 21:18:38 +0800
From:   Zeng Guang <guang.zeng@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        H Peter Anvin <hpa@...or.com>, kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Binbin Wu <binbin.wu@...ux.intel.com>,
        Zeng Guang <guang.zeng@...el.com>
Subject: [PATCH v2 2/8] KVM: x86: Use a new flag for branch instructions

From: Binbin Wu <binbin.wu@...ux.intel.com>

Use the new flag X86EMUL_F_BRANCH instead of X86EMUL_F_FETCH in
assign_eip(), since strictly speaking it is not behavior of instruction
fetch.

Another reason is to distinguish instruction fetch and execution of branch
instruction for feature(s) that handle differently on them.

Branch instruction is not data access instruction, so skip checking against
execute-only code segment as instruction fetch.

Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
Signed-off-by: Zeng Guang <guang.zeng@...el.com>
---
 arch/x86/kvm/emulate.c     | 5 +++--
 arch/x86/kvm/kvm_emulate.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 3ddfbc99fa4f..8e706d19ae45 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -721,7 +721,8 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
 		    (flags & X86EMUL_F_WRITE))
 			goto bad;
 		/* unreadable code segment */
-		if (!(flags & X86EMUL_F_FETCH) && (desc.type & 8) && !(desc.type & 2))
+		if (!(flags & (X86EMUL_F_FETCH | X86EMUL_F_BRANCH))
+			&& (desc.type & 8) && !(desc.type & 2))
 			goto bad;
 		lim = desc_limit_scaled(&desc);
 		if (!(desc.type & 8) && (desc.type & 4)) {
@@ -772,7 +773,7 @@ static inline int assign_eip(struct x86_emulate_ctxt *ctxt, ulong dst)
 	if (ctxt->op_bytes != sizeof(unsigned long))
 		addr.ea = dst & ((1UL << (ctxt->op_bytes << 3)) - 1);
 	rc = __linearize(ctxt, addr, &max_size, 1, ctxt->mode, &linear,
-			 X86EMUL_F_FETCH);
+			 X86EMUL_F_BRANCH);
 	if (rc == X86EMUL_CONTINUE)
 		ctxt->_eip = addr.ea;
 	return rc;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 86bbe997162d..9fc7d34a4ac1 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -91,6 +91,7 @@ struct x86_instruction_info {
 /* x86-specific emulation flags */
 #define X86EMUL_F_WRITE			BIT(0)
 #define X86EMUL_F_FETCH			BIT(1)
+#define X86EMUL_F_BRANCH		BIT(2)
 
 struct x86_emulate_ops {
 	void (*vm_bugged)(struct x86_emulate_ctxt *ctxt);
-- 
2.27.0