linux-kernel - Re: [PATCH v7 23/26] x86/traps: Fixup general protection faults caused by UMIP

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Date:   Fri, 9 Jun 2017 15:02:48 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        Alexandre Julliard <julliard@...ehq.org>,
        Stas Sergeev <stsp@...t.ru>, Fenghua Yu <fenghua.yu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-msdos@...r.kernel.org, wine-devel@...ehq.org,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v7 23/26] x86/traps: Fixup general protection faults
 caused by UMIP

On Fri, May 05, 2017 at 11:17:21AM -0700, Ricardo Neri wrote:
> If the User-Mode Instruction Prevention CPU feature is available and
> enabled, a general protection fault will be issued if the instructions
> sgdt, sldt, sidt, str or smsw are executed from user-mode context
> (CPL > 0). If the fault was caused by any of the instructions protected
> by UMIP, fixup_umip_exception will emulate dummy results for these

Please end function names with parentheses.

> instructions. If emulation is successful, the result is passed to the
> user space program and no SIGSEGV signal is emitted.
> 
> Please note that fixup_umip_exception also caters for the case when
> the fault originated while running in virtual-8086 mode.
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Chen Yucong <slaoub@...il.com>
> Cc: Chris Metcalf <cmetcalf@...lanox.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Huang Rui <ray.huang@....com>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Liang Z. Li <liang.z.li@...el.com>
> Cc: Alexandre Julliard <julliard@...ehq.org>
> Cc: Stas Sergeev <stsp@...t.ru>
> Cc: x86@...nel.org
> Cc: linux-msdos@...r.kernel.org
> Reviewed-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
>  arch/x86/kernel/traps.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 3995d3a..cec548d 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -65,6 +65,7 @@
>  #include <asm/trace/mpx.h>
>  #include <asm/mpx.h>
>  #include <asm/vm86.h>
> +#include <asm/umip.h>
>  
>  #ifdef CONFIG_X86_64
>  #include <asm/x86_init.h>
> @@ -526,6 +527,9 @@ do_general_protection(struct pt_regs *regs, long error_code)
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
>  	cond_local_irq_enable(regs);
>  

Almost definitely:

	if (static_cpu_has(X86_FEATURE_UMIP)) {
		if (...

> +	if (user_mode(regs) && fixup_umip_exception(regs))
> +		return;

We don't want to punish !UMIP machines.

-- 
Regards/Gruss,
    Boris.

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