linux-kernel - Re: [PATCH v7 1/5] x86/KASLR: Add kaslr

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Date:   Fri, 19 Jan 2018 10:34:05 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        tglx@...utronix.de, mingo@...hat.com, keescook@...omium.org,
        yasu.isimatu@...il.com, indou.takao@...fujitsu.com,
        lcapitulino@...hat.com
Subject: Re: [PATCH v7 1/5] x86/KASLR: Add kaslr_mem=nn[KMG]@ss[KMG]

On 01/17/18 at 06:53pm, Chao Fan wrote:
> Introduce a new kernel parameter kaslr_mem=nn[KMG]@ss[KMG] which is used
> by KASLR only during kernel decompression stage.
> 
> Users can use it to specify memory regions where kernel can be randomized
> into. E.g if movable_node specified in kernel cmdline, kernel could be
  ~ remove 'into'
> extracted into those movable regions, this will make memory hotplug fail.
> With the help of 'kaslr_mem=', limit kernel in those immovable regions
> specified.
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/compressed/kaslr.c | 73 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 70 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 8199a6187251..b21741135673 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -108,6 +108,15 @@ enum mem_avoid_index {
>  
>  static struct mem_vector mem_avoid[MEM_AVOID_MAX];
>  
> +/* Only support at most 4 usable memory regions specified for kaslr */
> +#define MAX_KASLR_MEM_USABLE	4
> +
> +/* Store the usable memory regions for kaslr */
> +static struct mem_vector mem_usable[MAX_KASLR_MEM_USABLE];

The name xx_usable sounds not so good, while I don't know what
is better. Otherwise this patch looks good to me.

Ack it.

Acked-by: Baoquan He <bhe@...hat.com>

> +
> +/* The amount of usable regions for kaslr user specify, not more than 4 */
> +static int num_usable_region;
> +
>  static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>  {
>  	/* Item one is entirely before item two. */
> @@ -206,7 +215,62 @@ static void mem_avoid_memmap(char *str)
>  		memmap_too_large = true;
>  }
>  
> -static int handle_mem_memmap(void)
> +static int parse_kaslr_mem(char *p,
> +			   unsigned long long *start,
> +			   unsigned long long *size)
> +{
> +	char *oldp;
> +
> +	if (!p)
> +		return -EINVAL;
> +
> +	oldp = p;
> +	*size = memparse(p, &p);
> +	if (p == oldp)
> +		return -EINVAL;
> +
> +	switch (*p) {
> +	case '@':
> +		*start = memparse(p + 1, &p);
> +		return 0;
> +	default:
> +		/*
> +		 * If w/o offset, only size specified, kaslr_mem=nn[KMG]
> +		 * has the same behaviour as kaslr_mem=nn[KMG]@0. It means
> +		 * the region starts from 0.
> +		 */
> +		*start = 0;
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static void parse_kaslr_mem_regions(char *str)
> +{
> +	static int i;
> +
> +	while (str && (i < MAX_KASLR_MEM_USABLE)) {
> +		int rc;
> +		unsigned long long start, size;
> +		char *k = strchr(str, ',');
> +
> +		if (k)
> +			*k++ = 0;
> +
> +		rc = parse_kaslr_mem(str, &start, &size);
> +		if (rc < 0)
> +			break;
> +		str = k;
> +
> +		mem_usable[i].start = start;
> +		mem_usable[i].size = size;
> +		i++;
> +	}
> +	num_usable_region = i;
> +}
> +
> +static int handle_mem_filter(void)
>  {
>  	char *args = (char *)get_cmd_line_ptr();
>  	size_t len = strlen((char *)args);
> @@ -214,7 +278,8 @@ static int handle_mem_memmap(void)
>  	char *param, *val;
>  	u64 mem_size;
>  
> -	if (!strstr(args, "memmap=") && !strstr(args, "mem="))
> +	if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
> +	    !strstr(args, "kaslr_mem="))
>  		return 0;
>  
>  	tmp_cmdline = malloc(len + 1);
> @@ -239,6 +304,8 @@ static int handle_mem_memmap(void)
>  
>  		if (!strcmp(param, "memmap")) {
>  			mem_avoid_memmap(val);
> +		} else if (!strcmp(param, "kaslr_mem")) {
> +			parse_kaslr_mem_regions(val);
>  		} else if (!strcmp(param, "mem")) {
>  			char *p = val;
>  
> @@ -378,7 +445,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>  	/* We don't need to set a mapping for setup_data. */
>  
>  	/* Mark the memmap regions we need to avoid */
> -	handle_mem_memmap();
> +	handle_mem_filter();
>  
>  #ifdef CONFIG_X86_VERBOSE_BOOTUP
>  	/* Make sure video RAM can be used. */
> -- 
> 2.14.3
> 
> 
>