linux-kernel - Re: [PATCH] x86/asm/entry/64: Fix MSR_IA32_SYSENTER

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Date:	Fri, 3 Apr 2015 13:20:27 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Will Drewry <wad@...omium.org>
Subject: Re: [PATCH] x86/asm/entry/64: Fix MSR_IA32_SYSENTER_CS MSR value

On Fri, Apr 03, 2015 at 11:42:10AM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Commit
> 
>   d56fe4bf5f3c ("x86/asm/entry/64: Always set up SYSENTER MSRs")
> 
> missed to add "ULL" to the 0 and wrmsrl_safe() complains:
> 
>   arch/x86/kernel/cpu/common.c: In function ‘syscall_init’:
>   arch/x86/kernel/cpu/common.c:1226:2: warning: right shift count >= width of type
>     wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0);
> 
> Fix it.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Alexei Starovoitov <ast@...mgrid.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Will Drewry <wad@...omium.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> ---
>  arch/x86/kernel/cpu/common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index bb6633a87a19..2c249b57e4b5 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1223,7 +1223,7 @@ void syscall_init(void)
>  	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)ia32_sysenter_target);
>  #else
>  	wrmsrl(MSR_CSTAR, ignore_sysret);
> -	wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0);
> +	wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0ULL);

Btw, we probably should define an invalid segment

#define GDT_ENTRY_INVALID_SEGMENT		0ULL

and use that value instead of the naked 0.

-- 
Regards/Gruss,
    Boris.

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