linux-kernel - Re: [PATCH] x86: Preserve iopl on fork and execve

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Message-ID: <555117B7.6040608@zytor.com>
Date:	Mon, 11 May 2015 13:57:27 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alex Henrie <alexhenrie24@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Doug Johnson <dougvj@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Tyler Hicks <tyhicks@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Preserve iopl on fork and execve

On 05/11/2015 01:49 PM, Alex Henrie wrote:
> Signed-off-by: Alex Henrie <alexhenrie24@...il.com>
> Suggested-by: Doug Johnson <dougvj@...gvj.net>
> ---
>  arch/x86/kernel/process_32.c | 2 +-
>  arch/x86/kernel/process_64.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 8ed2106..86bfe7c 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -205,7 +205,7 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
>  	regs->cs		= __USER_CS;
>  	regs->ip		= new_ip;
>  	regs->sp		= new_sp;
> -	regs->flags		= X86_EFLAGS_IF;
> +	regs->flags		|= X86_EFLAGS_IF;
>  	force_iret();
>  }
>  EXPORT_SYMBOL_GPL(start_thread);
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index ddfdbf7..fc22e5d 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -238,7 +238,7 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip,
>  	regs->sp		= new_sp;
>  	regs->cs		= _cs;
>  	regs->ss		= _ss;
> -	regs->flags		= X86_EFLAGS_IF;
> +	regs->flags		|= X86_EFLAGS_IF;
>  	force_iret();
>  }
>  

This would seem to preserve a whole bunch of other flags that should not
be leaked between processes, such as DF or TF.

	-hpa


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