From 8a4a164f3e33be9b2d28d54fe430e92f40626054 Mon Sep 17 00:00:00 2001

From: Cyrill Gorcunov <gorcunov@openvz.org>

Date: Mon, 26 Jun 2017 23:55:28 +0300

Subject: [PATCH 1/2] kerndat: Detect if we have guard page mangle in procfs

 output

In vanilla kernel commit 1be7107fbe18eed3e319a6c3e83c78254b693acb

show_map_vma() no longer report PAGE_SIZE. Detect it with

simple test and remember in kdat settings.

Suggested-by: Oleg Nesterov <oleg@redhat.com>

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>

Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

---

 criu/include/kerndat.h |  1 +

 criu/kerndat.c         | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++

 2 files changed, 77 insertions(+)

diff --git a/criu/include/kerndat.h b/criu/include/kerndat.h

index ba8c10da7..891cbdd41 100644

--- a/criu/include/kerndat.h

+++ b/criu/include/kerndat.h

@@ -44,6 +44,7 @@ struct kerndat_s {

 	unsigned int has_xtlocks;

 	unsigned long mmap_min_addr;

 	bool has_tcp_half_closed;

+	bool stack_guard_gap_hidden;

 };

 extern struct kerndat_s kdat;

diff --git a/criu/kerndat.c b/criu/kerndat.c

index 354fb672b..80ec58bcf 100644

--- a/criu/kerndat.c

+++ b/criu/kerndat.c

@@ -563,6 +563,80 @@ int kerndat_tcp_repair(void)

 	return exit_code;

 }

+static int kerndat_detect_stack_guard_gap(void)

+{

+	int num, ret = -1, detected = 0;

+	unsigned long start, end;

+	char r, w, x, s;

+	char buf[1024];

+	FILE *maps;

+	void *mem;

+

+	mem = mmap(NULL, (3ul << 20), PROT_READ | PROT_WRITE,

+		   MAP_PRIVATE | MAP_ANONYMOUS | MAP_GROWSDOWN, -1, 0);

+	if (mem == MAP_FAILED) {

+		pr_perror("Can't mmap stack area");

+		return -1;

+	}

+	munmap(mem, (3ul << 20));

+

+	mem = mmap(mem + (2ul << 20), (1ul << 20), PROT_READ | PROT_WRITE,

+		   MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED | MAP_GROWSDOWN, -1, 0);

+	if (mem == MAP_FAILED) {

+		pr_perror("Can't mmap stack area");

+		return -1;

+	}

+

+	maps = fopen("/proc/self/maps", "r");

+	if (maps == NULL) {

+		munmap(mem, 4096);

+		return -1;

+	}

+

+	while (fgets(buf, sizeof(buf), maps)) {

+		num = sscanf(buf, "%lx-%lx %c%c%c%c",

+			     &start, &end, &r, &w, &x, &s);

+		if (num < 6) {

+			pr_err("Can't parse: %s\n", buf);

+			goto err;

+		}

+

+		/*

+		 * When reading /proc/$pid/[s]maps the

+		 * start/end addresses migh be cutted off

+		 * with PAGE_SIZE on kernels prior 4.12

+		 * (see kernel commit 1be7107fbe18ee).

+		 *

+		 * Same time there was semi-complete

+		 * patch released which hitted a number

+		 * of repos (Ubuntu, Fedora) where instead

+		 * of PAGE_SIZE the 1M gap is cutted off.

+		 */

+		if (start == (unsigned long)mem) {

+			kdat.stack_guard_gap_hidden = false;

+			detected = 1;

+			break;

+		} else if (start == ((unsigned long)mem + (1ul << 20))) {

+			pr_warn("Unsupported stack guard detected, confused but continue\n");

+			kdat.stack_guard_gap_hidden = true;

+			detected = 1;

+			break;

+		} else if (start == ((unsigned long)mem + PAGE_SIZE)) {

+			kdat.stack_guard_gap_hidden = true;

+			detected = 1;

+			break;

+		}

+	}

+

+	if (detected)

+		ret = 0;

+

+err:

+	munmap(mem, (1ul << 20));

+	fclose(maps);

+	return ret;

+}

+

 int kerndat_init(void)

 {

 	int ret;

@@ -676,6 +750,8 @@ int kerndat_init(void)

 		ret = kerndat_iptables_has_xtlocks();

 	if (!ret)

 		ret = kerndat_tcp_repair();

+	if (!ret)

+		ret = kerndat_detect_stack_guard_gap();

 	kerndat_lsm();

 	kerndat_mmap_min_addr();

-- 

2.13.0