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Date: Tue, 23 Jan 2018 21:28:59 +0100
From: Borislav Petkov <bp@alien8.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>, linux-kernel@vger.kernel.org,
	Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Jason Baron <jbaron@akamai.com>
Subject: Re: [PATCH 06/24] x86,kvm: Fix indirect calls in emulator
Message-ID: <20180123202859.qc5frxyonavtkhpz@pd.tnic>
References: <20180123152539.374360046@infradead.org>
 <20180123152638.336674335@infradead.org>
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On Tue, Jan 23, 2018 at 04:25:45PM +0100, Peter Zijlstra wrote:
> Replace the indirect calls with CALL_NOSPEC.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  arch/x86/kvm/emulate.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> --- 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(unsign
>  	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));

Oh, "thunk_target" is magical.

-- 
Regards/Gruss,
    Boris.

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