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Date: Tue, 14 Feb 2017 11:42:59 -0800
From: Thomas Garnier <thgarnie@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Thomas Garnier <thgarnie@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>,
	Pavel Machek <pavel@....cz>,
	Jiri Kosina <jikos@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Juergen Gross <jgross@...e.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"Luis R . Rodriguez" <mcgrof@...nel.org>,
	He Chen <he.chen@...ux.intel.com>,
	Brian Gerst <brgerst@...il.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Adam Buchbinder <adam.buchbinder@...il.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Joerg Roedel <joro@...tes.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>
Cc: x86@...nel.org,
	linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com,
	linux-pm@...r.kernel.org,
	linux-efi@...r.kernel.org,
	xen-devel@...ts.xenproject.org,
	lguest@...ts.ozlabs.org,
	kvm@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: [PATCH v3 4/4] KVM: VMX: Simplify segment_base

The KVM segment_base function is confusing. This patch replaces integers
with appropriate flags, simplify constructs and add comments.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
Based on next-20170213
---
 arch/x86/kvm/vmx.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 99167f20bc34..edb8326108dd 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2062,25 +2062,35 @@ static unsigned long segment_base(u16 selector)
 	struct desc_struct *d;
 	unsigned long table_base;
 	unsigned long v;
+	u32 high32;
 
-	if (!(selector & ~3))
+	if (!(selector & ~SEGMENT_RPL_MASK))
 		return 0;
 
-	table_base = get_current_gdt_rw_vaddr();
-
-	if (selector & 4) {           /* from ldt */
+	/* LDT selector */
+	if ((selector & SEGMENT_TI_MASK) == SEGMENT_LDT) {
 		u16 ldt_selector = kvm_read_ldt();
 
-		if (!(ldt_selector & ~3))
+		if (!(ldt_selector & ~SEGMENT_RPL_MASK))
 			return 0;
 
 		table_base = segment_base(ldt_selector);
+	} else {
+		table_base = get_current_gdt_rw_vaddr();
 	}
-	d = (struct desc_struct *)(table_base + (selector & ~7));
+
+	d = (struct desc_struct *)table_base + (selector >> 3);
 	v = get_desc_base(d);
 #ifdef CONFIG_X86_64
-       if (d->s == 0 && (d->type == 2 || d->type == 9 || d->type == 11))
-               v |= ((unsigned long)((struct ldttss_desc64 *)d)->base3) << 32;
+	/*
+	 * Extend the virtual address if we have a system descriptor entry for
+	 * LDT or TSS (available or busy).
+	 */
+	if (d->s == 0 && (d->type == DESC_LDT || d->type == DESC_TSS ||
+			  d->type == 11/*Busy TSS */)) {
+		high32 = ((struct ldttss_desc64 *)d)->base3;
+		v |= (u64)high32 << 32;
+	}
 #endif
 	return v;
 }
-- 
2.11.0.483.g087da7b7c-goog

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