Re: [PATCH v6 5/5] kaslr: add kaslr_mem=nn[KMG]!ss[KMG] to avoid memory regions

[Baoquan He]

On 01/15/18 at 08:49pm, Chao Fan wrote:
> Hi Luiz,
> 
> I don't know if this patch is OK for you.
> Of coure you can only use kaslr_mem=nn@ss to solve the 1G huge page
> issue. Because we know the region [0,1G] is not suitable for 1G huge
> page, so you can specify ksalr_mem=1G@0 of kaslr_mem=1G to solve
> your problem. But the regions may be too slow and is not good
> for the randomness.

I guess you want to say:

"Because we know the region [0,1G] is not suitable for 1G huge page, so
you can specify ksalr_mem=1G@0 or kaslr_mem=1G to solve your problem.
But the region may be too small and is not good for the randomness."

Hi Luiz,

For hugetlb issue, we can always suggest users adding "kaslr_mem=1G" to
kernel cmdline on KVM. Surely if users are very familiar with system
memory layout, they can specify "kaslr_mem=1G, kaslr_mem=1G@2G
kaslr_mem=1G@4G" for better kernel text KASLR. The "kaslr_mem=1G"
suggestion can be documented for redhat kvm usage. Any thought or
suggestion?

Thanks
Baoquan

> 
> So as Kess said, I put the regions suitable for 1G huge page to
> mem_avoid, you can use kaslr_mem=1G!1G to solve the problem in your
> email.
> 
> Thanks,
> Chao Fan
> 
> On Mon, Jan 15, 2018 at 08:40:16PM +0800, Chao Fan wrote:
> >In current code, kaslr choose the only suitable memory region for 1G
> >huge page, so the no suitable region for 1G huge page. So add this
> >feature to store these regions.
> >
> >Of coure, we can use memmap= to do this job. But memmap will be handled
> >in the later code, but kaslr_mem= only works in this period.
> >
> >It can help users to avoid more memory regions, not only the 1G huge
> >huge page issue.
> >
> >Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
> >---
> > arch/x86/boot/compressed/kaslr.c | 56 +++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 50 insertions(+), 6 deletions(-)
> >
> >diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> >index fc531fa1f10c..c71189cf8d56 100644
> >--- a/arch/x86/boot/compressed/kaslr.c
> >+++ b/arch/x86/boot/compressed/kaslr.c
> >@@ -95,6 +95,18 @@ static bool memmap_too_large;
> > /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
> > unsigned long long mem_limit = ULLONG_MAX;
> > 
> >+/*
> >+ * Only supporting at most 4 unusable memory regions for
> >+ * "kaslr_mem=nn[KMG]!ss[KMG]"
> >+ */
> >+#define MAX_KASLR_MEM_AVOID	4
> >+
> >+static bool kaslr_mem_avoid_too_large;
> >+
> >+enum kaslr_mem_type {
> >+	CMD_MEM_USABLE = 1,
> >+	CMD_MEM_AVOID,
> >+};
> > 
> > enum mem_avoid_index {
> > 	MEM_AVOID_ZO_RANGE = 0,
> >@@ -103,6 +115,8 @@ enum mem_avoid_index {
> > 	MEM_AVOID_BOOTPARAMS,
> > 	MEM_AVOID_MEMMAP_BEGIN,
> > 	MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
> >+	MEM_AVOID_KASLR_MEM_BEGIN,
> >+	MEM_AVOID_KASLR_MEM_END = MEM_AVOID_KASLR_MEM_BEGIN + MAX_KASLR_MEM_AVOID - 1,
> > 	MEM_AVOID_MAX,
> > };
> > 
> >@@ -217,7 +231,8 @@ static void mem_avoid_memmap(char *str)
> > 
> > static int parse_kaslr_mem(char *p,
> > 			   unsigned long long *start,
> >-			   unsigned long long *size)
> >+			   unsigned long long *size,
> >+			   int *cmd_type)
> > {
> > 	char *oldp;
> > 
> >@@ -230,8 +245,13 @@ static int parse_kaslr_mem(char *p,
> > 		return -EINVAL;
> > 
> > 	switch (*p) {
> >+	case '!' :
> >+		*start = memparse(p + 1, &p);
> >+		*cmd_type = CMD_MEM_AVOID;
> >+		return 0;
> > 	case '@':
> > 		*start = memparse(p + 1, &p);
> >+		*cmd_type = CMD_MEM_USABLE;
> > 		return 0;
> > 	default:
> > 		/*
> >@@ -240,6 +260,7 @@ static int parse_kaslr_mem(char *p,
> > 		 * the region starts from 0.
> > 		 */
> > 		*start = 0;
> >+		*cmd_type = CMD_MEM_USABLE;
> > 		return 0;
> > 	}
> > 
> >@@ -248,26 +269,44 @@ static int parse_kaslr_mem(char *p,
> > 
> > static void parse_kaslr_mem_regions(char *str)
> > {
> >-	static int i;
> >+	static int i = 0, j = 0;
> >+	int cmd_type = 0;
> > 
> > 	while (str && (i < MAX_KASLR_MEM_USABLE)) {
> > 		int rc;
> > 		unsigned long long start, size;
> > 		char *k = strchr(str, ',');
> > 
> >+		if (i >= MAX_KASLR_MEM_USABLE && j >= MAX_KASLR_MEM_AVOID)
> >+			break;
> >+
> > 		if (k)
> > 			*k++ = 0;
> > 
> >-		rc = parse_kaslr_mem(str, &start, &size);
> >+		rc = parse_kaslr_mem(str, &start, &size, &cmd_type);
> > 		if (rc < 0)
> > 			break;
> > 		str = k;
> > 
> >-		mem_usable[i].start = start;
> >-		mem_usable[i].size = size;
> >-		i++;
> >+		if (cmd_type == CMD_MEM_USABLE) {
> >+			if (i >= MAX_KASLR_MEM_USABLE)
> >+				continue;
> >+			mem_usable[i].start = start;
> >+			mem_usable[i].size = size;
> >+			i++;
> >+		} else if (cmd_type == CMD_MEM_AVOID) {
> >+			if (j >= MAX_KASLR_MEM_AVOID)
> >+				continue;
> >+			mem_avoid[MEM_AVOID_KASLR_MEM_BEGIN + j].start = start;
> >+			mem_avoid[MEM_AVOID_KASLR_MEM_BEGIN + j].size = size;
> >+			j++;
> >+		}
> > 	}
> > 	num_usable_region = i;
> >+
> >+	/* More than 4 kaslr_mem avoid, fail kaslr */
> >+	if ((j >= MAX_KASLR_MEM_AVOID) && str)
> >+		kaslr_mem_avoid_too_large = true;
> > }
> > 
> > static int handle_mem_filter(void)
> >@@ -799,6 +838,11 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
> > 		return 0;
> > 	}
> > 
> >+	/* Check if we had too many kaslr_mem avoid. */
> >+	if (kaslr_mem_avoid_too_large) {
> >+		debug_putstr("Aborted memory entries scan (more than 4 kaslr_mem avoid args)!\n");
> >+		return 0;
> >+	}
> > 	/* Make sure minimum is aligned. */
> > 	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
> > 
> >-- 
> >2.14.3
> >
> 
>