linux-kernel - [tip:x86/pti] KVM: x86: Make indirect calls in emulator speculation safe

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Date:   Thu, 25 Jan 2018 02:34:12 -0800
From:   tip-bot for Peter Zijlstra <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, jpoimboe@...hat.com, dan.j.williams@...el.com,
        ashok.raj@...el.com, aarcange@...hat.com, jun.nakajima@...el.com,
        luto@...nel.org, torvalds@...ux-foundation.org,
        arjan.van.de.ven@...el.com, hpa@...or.com,
        tim.c.chen@...ux.intel.com, dwmw@...zon.co.uk,
        gregkh@...uxfoundation.org, asit.k.mallick@...el.com,
        jbaron@...mai.com, pbonzini@...hat.com, ak@...ux.intel.com,
        mingo@...nel.org, dwmw2@...radead.org, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: [tip:x86/pti] KVM: x86: Make indirect calls in emulator speculation
 safe

Commit-ID:  1a29b5b7f347a1a9230c1e0af5b37e3e571588ab
Gitweb:     https://git.kernel.org/tip/1a29b5b7f347a1a9230c1e0af5b37e3e571588ab
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 25 Jan 2018 10:58:13 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 25 Jan 2018 11:30:07 +0100

KVM: x86: Make indirect calls in emulator speculation safe

Replace the indirect calls with CALL_NOSPEC.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Ashok Raj <ashok.raj@...el.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Jun Nakajima <jun.nakajima@...el.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: rga@...zon.de
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Asit Mallick <asit.k.mallick@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Jason Baron <jbaron@...mai.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Arjan Van De Ven <arjan.van.de.ven@...el.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Link: https://lkml.kernel.org/r/20180125095843.595615683@infradead.org

---
 arch/x86/kvm/emulate.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index d90cdc7..453d8c9 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -25,6 +25,7 @@
 #include <asm/kvm_emulate.h>
 #include <linux/stringify.h>
 #include <asm/debugreg.h>
+#include <asm/nospec-branch.h>
 
 #include "x86.h"
 #include "tss.h"
@@ -1021,8 +1022,8 @@ static __always_inline u8 test_cc(unsigned int condition, unsigned long flags)
 	void (*fop)(void) = (void *)em_setcc + 4 * (condition & 0xf);
 
 	flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
-	asm("push %[flags]; popf; call *%[fastop]"
-	    : "=a"(rc) : [fastop]"r"(fop), [flags]"r"(flags));
+	asm("push %[flags]; popf; " CALL_NOSPEC
+	    : "=a"(rc) : [thunk_target]"r"(fop), [flags]"r"(flags));
 	return rc;
 }
 
@@ -5305,9 +5306,9 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
 	if (!(ctxt->d & ByteOp))
 		fop += __ffs(ctxt->dst.bytes) * FASTOP_SIZE;
 
-	asm("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n"
+	asm("push %[flags]; popf; " CALL_NOSPEC " ; pushf; pop %[flags]\n"
 	    : "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags),
-	      [fastop]"+S"(fop), ASM_CALL_CONSTRAINT
+	      [thunk_target]"+S"(fop), ASM_CALL_CONSTRAINT
 	    : "c"(ctxt->src2.val));
 
 	ctxt->eflags = (ctxt->eflags & ~EFLAGS_MASK) | (flags & EFLAGS_MASK);