linux-kernel - Re: [PATCH] unicore32: use get_kernel_nofault in dump mem and dump

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Date:   Tue, 21 Jul 2020 10:09:20 +0800 (GMT+08:00)
From:   "Guan Xuetao" <gxt@....edu.cn>
To:     "christoph hellwig" <hch@....de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] unicore32: use get_kernel_nofault in dump mem and
 dump_instr

Very good to remove ds/fs in unicore arch.
Could u send me full patch for test?

Guan Xuetao


> -----原始邮件-----
> 发件人: "Christoph Hellwig" <hch@....de>
> 发送时间: 2020-07-20 19:43:58 (星期一)
> 收件人: gxt@....edu.cn
> 抄送: linux-kernel@...r.kernel.org
> 主题: [PATCH] unicore32: use get_kernel_nofault in dump mem and dump_instr
> 
> Use the proper get_kernel_nofault helper to access an unsafe kernel
> pointer without faulting instead of playing with set_fs and get_user.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/unicore32/kernel/traps.c | 28 +++-------------------------
>  1 file changed, 3 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/unicore32/kernel/traps.c b/arch/unicore32/kernel/traps.c
> index a3ac01df1a2e43..c1964a4a1edbb0 100644
> --- a/arch/unicore32/kernel/traps.c
> +++ b/arch/unicore32/kernel/traps.c
> @@ -65,17 +65,8 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
>  		     unsigned long top)
>  {
>  	unsigned long first;
> -	mm_segment_t fs;
>  	int i;
>  
> -	/*
> -	 * We need to switch to kernel mode so that we can use __get_user
> -	 * to safely read from kernel space.  Note that we now dump the
> -	 * code first, just in case the backtrace kills us.
> -	 */
> -	fs = get_fs();
> -	set_fs(KERNEL_DS);
> -
>  	printk(KERN_DEFAULT "%s%s(0x%08lx to 0x%08lx)\n",
>  			lvl, str, bottom, top);
>  
> @@ -89,7 +80,8 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
>  		for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
>  			if (p >= bottom && p < top) {
>  				unsigned long val;
> -				if (__get_user(val, (unsigned long *)p) == 0)
> +				if (get_kernel_nofault(val, (unsigned long *)p)
> +						== 0)
>  					sprintf(str + i * 9, " %08lx", val);
>  				else
>  					sprintf(str + i * 9, " ????????");
> @@ -97,31 +89,19 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
>  		}
>  		printk(KERN_DEFAULT "%s%04lx:%s\n", lvl, first & 0xffff, str);
>  	}
> -
> -	set_fs(fs);
>  }
>  
>  static void dump_instr(const char *lvl, struct pt_regs *regs)
>  {
>  	unsigned long addr = instruction_pointer(regs);
>  	const int width = 8;
> -	mm_segment_t fs;
>  	char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
>  	int i;
>  
> -	/*
> -	 * We need to switch to kernel mode so that we can use __get_user
> -	 * to safely read from kernel space.  Note that we now dump the
> -	 * code first, just in case the backtrace kills us.
> -	 */
> -	fs = get_fs();
> -	set_fs(KERNEL_DS);
> -
>  	for (i = -4; i < 1; i++) {
>  		unsigned int val, bad;
>  
> -		bad = __get_user(val, &((u32 *)addr)[i]);
> -
> +		bad = get_kernel_nofault(val, &((u32 *)addr)[i]);
>  		if (!bad)
>  			p += sprintf(p, i == 0 ? "(%0*x) " : "%0*x ",
>  					width, val);
> @@ -131,8 +111,6 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
>  		}
>  	}
>  	printk(KERN_DEFAULT "%sCode: %s\n", lvl, str);
> -
> -	set_fs(fs);
>  }
>  
>  static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
> -- 
> 2.27.0