linux-kernel - Re: [patch 37/60] x86mm//kpti: Force entry through trampoline when KPTI active

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Date:   Wed, 6 Dec 2017 17:01:22 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>, keescook@...gle.com,
        hughd@...gle.com, Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>, daniel.gruss@...k.tugraz.at
Subject: Re: [patch 37/60] x86mm//kpti: Force entry through trampoline when
 KPTI active

On Mon, Dec 04, 2017 at 03:07:43PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.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@...utronix.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@...e.de>

-- 
Regards/Gruss,
    Boris.

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