linux-kernel - Re: [PATCH v6 1/5] kaslr: add kaslr_mem=nn[KMG]@ss[KMG] to specify extracting memory

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Date:   Mon, 15 Jan 2018 20:43:50 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bhe@...hat.com>,
        <keescook@...omium.org>, <yasu.isimatu@...il.com>
CC:     <indou.takao@...fujitsu.com>, <lcapitulino@...hat.com>
Subject: Re: [PATCH v6 1/5] kaslr: add kaslr_mem=nn[KMG]@ss[KMG] to specify
 extracting memory

On Mon, Jan 15, 2018 at 08:40:12PM +0800, Chao Fan wrote:
>In current code, kaslr only has a method to avoid some memory regions,
>but no method to specify the regions for kaslr to extract. So kaslr
>may choose the wrong position sometimes, which will cause some other
>features fail.
>
>Here is a problem that kaslr may choose the memory region in movable
>nodes to extract kernel, which will make the nodes can't be hot-removed.
>To solve it, we can specify the memory region in immovable node.
>Create "kaslr_mem=" to store the regions in immovable nodes, where should
>be chosen by kaslr.
>
>Also change the "handle_mem_memmap" to "handle_mem_filter", since
>it will not only handle memmap parameter now.
>
>Multiple regions can be specified, comma delimited.
>Considering the usage of memory, only support for 4 regions.
>4 regions contains 2 nodes at least, enough for kernel to extract.
>
>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..b071f6edd7b2 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];

Here it may should be "kaslr_mem", but there is mem_avoid in current
code, so I name it as "mem_usable" to be symmetrical with "mem_avoid".
We can see more in PATCH 05.

Thanks,
Chao Fan

>+
>+/* 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
>