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Date: Wed, 6 Dec 2017 17:01:22 +0100
From: Borislav Petkov <bp@suse.de>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Eduardo Valentin <eduval@amazon.com>, aliguori@amazon.com,
        Will Deacon <will.deacon@arm.com>, daniel.gruss@iaik.tugraz.at
Subject: Re: [patch 37/60] x86mm//kpti: Force entry through trampoline when
 KPTI active
Message-ID: <20171206160122.p6i7j53pl7c7se3d@pd.tnic>
References: <20171204140706.296109558@linutronix.de>
 <20171204150607.882901465@linutronix.de>
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On Mon, Dec 04, 2017 at 03:07:43PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> Force the entry through the trampoline only when KPTI is active. Otherwise
> go through the normal entry code.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> 
> ---
>  arch/x86/kernel/cpu/common.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1458,7 +1458,10 @@ void syscall_init(void)
>  		(entry_SYSCALL_64_trampoline - _entry_trampoline);
>  
>  	wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
> -	wrmsrl(MSR_LSTAR, SYSCALL64_entry_trampoline);
> +	if (static_cpu_has_bug(X86_BUG_CPU_SECURE_MODE_KPTI))
> +		wrmsrl(MSR_LSTAR, SYSCALL64_entry_trampoline);
> +	else
> +		wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);
>  
>  #ifdef CONFIG_IA32_EMULATION
>  	wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);

Just a nitpick:

Subject: x86/mm/kpti:...

Otherwise,

Reviewed-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--