linux-kernel - Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32

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Message-ID: <20150423101840.GC28327@pd.tnic>
Date:	Thu, 23 Apr 2015 12:18:40 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32_DS to
 %ss

On Thu, Apr 23, 2015 at 11:56:21AM +0200, Denys Vlasenko wrote:
> The fix can look like this (untested):
> 
> 
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index 0c302d0..9f4c232 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -198,6 +198,18 @@ sysexit_from_sys_call:
>  	 * with 'sysenter' and it uses the SYSENTER calling convention.
>  	 */
>  	andl    $~TS_COMPAT,ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
> +	/*
> +	 * On AMD, SYSRET32 does not modify %ss cached descriptor;

Ok, but doc says that in both long and compat mode, SYSRET does load
SS.sel with the value in MSR_STAR...

Hmmm.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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