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Date: Thu, 9 Mar 2017 09:42:08 +0100
From: Borislav Petkov <bp@...en8.de>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: David Howells <dhowells@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>,
	Al Viro <viro@...iv.linux.org.uk>,
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	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	"David S . Miller" <davem@...emloft.net>,
	Andy Lutomirski <luto@...nel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
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	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
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	Pratyush Anand <panand@...hat.com>,
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	Chris Metcalf <cmetcalf@...lanox.com>,
	Andre Przywara <andre.przywara@....com>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 1/4] syscalls: Restore address limit after a syscall

On Wed, Mar 08, 2017 at 05:24:53PM -0800, Thomas Garnier wrote:
> @@ -191,6 +191,22 @@ extern struct trace_event_functions exit_syscall_print_funcs;
>  	SYSCALL_METADATA(sname, x, __VA_ARGS__)			\
>  	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>  
> +asmlinkage void verify_pre_usermode_state(void);
> +
> +#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
> +static inline bool has_user_ds(void) {
> +	bool ret = segment_eq(get_fs(), USER_DS);
> +	// Prevent re-ordering the call

This is not the kernel comments style. Use /* */ instead.

> +	barrier();
> +	return ret;
> +}
> +#else
> +static inline bool has_user_ds(void) {
> +	return false;
> +}
> +#endif

... and then you could slim down the ifdeffery a bit:

static inline bool has_user_ds(void) {
	bool ret = false;

#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
	ret = segment_eq(get_fs(), USER_DS);
	/* Prevent re-ordering the call. */
	barrier();
#endif

	return ret;
}

-- 
Regards/Gruss,
    Boris.

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