linux-kernel - Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140729193232.GA8153@redhat.com>
Date:	Tue, 29 Jul 2014 21:32:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	Will Drewry <wad@...omium.org>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linux-arch@...r.kernel.org, linux-security-module@...r.kernel.org,
	Alexei Starovoitov <ast@...mgrid.com>, hpa@...or.com,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ

On 07/28, Andy Lutomirski wrote:
>
> @@ -1449,7 +1449,12 @@ long syscall_trace_enter(struct pt_regs *regs)
>  {
>  	long ret = 0;
>  
> -	user_exit();
> +	/*
> +	 * If TIF_NOHZ is set, we are required to call user_exit() before
> +	 * doing anything that could touch RCU.
> +	 */
> +	if (test_thread_flag(TIF_NOHZ))
> +		user_exit();

Personally I still think this change just adds more confusion, but I leave
this to you and Frederic.

It is not that "If TIF_NOHZ is set, we are required to call user_exit()", we
need to call user_exit() just because we enter the kernel. TIF_NOHZ is just
the implementation detail which triggers this slow path.

At least it should be correct, unless I am confused even more than I think.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/