UBUNTU-CVE-2025-68211
In the Linux kernel, the following vulnerability has been resolved: ksm: use range-walk function to jump over holes in scan_get_next_rmap_item Currently, scan_get_next_rmap_item() walks every page address in a VMA to locate mergeable pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions, causing ksmd to use large amount of cpu without deduplicating much pages. This patch replaces the per-address lookup with a range walk using walk_page_range(). The range walker allows KSM to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. This problem was previously discussed in [1]. Consider the following test program which creates a 32 TiB mapping in the virtual address space but only populates a single page: #include <unistd.h> #include <stdio.h> #include <sys/mman.h> /* 32 TiB */ const size_t size = 32ul * 1024 * 1024 * 1024 * 1024; int main() { char *area = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0); if (area == MAP_FAILED) { perror("mmap() failed\n"); return -1; } /* Populate a single page such that we get an anon_vma. */ *area = 0; /* Enable KSM. */ madvise(area, size, MADV_MERGEABLE); pause(); return 0; } $ ./ksm-sparse & $ echo 1 > /sys/kernel/mm/ksm/run Without this patch ksmd uses 100% of the cpu for a long time (more then 1 hour in my test machine) scanning all the 32 TiB virtual address space that contain only one mapped page. This makes ksmd essentially deadlocked not able to deduplicate anything of value. With this patch ksmd walks only the one mapped page and skips the rest of the 32 TiB virtual address space, making the scan fast using little cpu.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
53 explicit affected versions
116 explicit affected versions
82 explicit affected versions
50 explicit affected versions
6 explicit affected versions
12 explicit affected versions
19 explicit affected versions
10 explicit affected versions
6 explicit affected versions
92 explicit affected versions
24 explicit affected versions
77 explicit affected versions
77 explicit affected versions
91 explicit affected versions
80 explicit affected versions
72 explicit affected versions
10 explicit affected versions
39 explicit affected versions
26 explicit affected versions
84 explicit affected versions
191 explicit affected versions
7 explicit affected versions
79 explicit affected versions
42 explicit affected versions
13 explicit affected versions
85 explicit affected versions
46 explicit affected versions
35 explicit affected versions
44 explicit affected versions
42 explicit affected versions
18 explicit affected versions
36 explicit affected versions
118 explicit affected versions
64 explicit affected versions
48 explicit affected versions
120 explicit affected versions
13 explicit affected versions
4 explicit affected versions
121 explicit affected versions
23 explicit affected versions
55 explicit affected versions
124 explicit affected versions
1 explicit affected versions
1 explicit affected versions
21 explicit affected versions
9 explicit affected versions
16 explicit affected versions
10 explicit affected versions
12 explicit affected versions
76 explicit affected versions
51 explicit affected versions
8 explicit affected versions
7 explicit affected versions
12 explicit affected versions
11 explicit affected versions
111 explicit affected versions
7 explicit affected versions
12 explicit affected versions
14 explicit affected versions
10 explicit affected versions
1 explicit affected versions
7 explicit affected versions
19 explicit affected versions
104 explicit affected versions
12 explicit affected versions
1 explicit affected versions
105 explicit affected versions
12 explicit affected versions
44 explicit affected versions
120 explicit affected versions
38 explicit affected versions
16 explicit affected versions
9 explicit affected versions
29 explicit affected versions
37 explicit affected versions
10 explicit affected versions
37 explicit affected versions
10 explicit affected versions
1 explicit affected versions
13 explicit affected versions
42 explicit affected versions
3 explicit affected versions
10 explicit affected versions
11 explicit affected versions
59 explicit affected versions
1 explicit affected versions
26 explicit affected versions
12 explicit affected versions
13 explicit affected versions
144 explicit affected versions
32 explicit affected versions
1 explicit affected versions
29 explicit affected versions
111 explicit affected versions
13 explicit affected versions
12 explicit affected versions
89 explicit affected versions
43 explicit affected versions
43 explicit affected versions
1 explicit affected versions
100 explicit affected versions
84 explicit affected versions
47 explicit affected versions
33 explicit affected versions
23 explicit affected versions
53 explicit affected versions
10 explicit affected versions
23 explicit affected versions
188 explicit affected versions
22 explicit affected versions
11 explicit affected versions
5 explicit affected versions
12 explicit affected versions
1 explicit affected versions
7 explicit affected versions
12 explicit affected versions
8 explicit affected versions
138 explicit affected versions
2 explicit affected versions
5 explicit affected versions
69 explicit affected versions
132 explicit affected versions
85 explicit affected versions
165 explicit affected versions
154 explicit affected versions
10 explicit affected versions
26 explicit affected versions
42 explicit affected versions
1 explicit affected versions
61 explicit affected versions
37 explicit affected versions
48 explicit affected versions
11 explicit affected versions
1 explicit affected versions
13 explicit affected versions
48 explicit affected versions
139 explicit affected versions
78 explicit affected versions
16 explicit affected versions
83 explicit affected versions
53 explicit affected versions
116 explicit affected versions
3 explicit affected versions
132 explicit affected versions
93 explicit affected versions
1 explicit affected versions
7 explicit affected versions
2 explicit affected versions
7 explicit affected versions
51 explicit affected versions
8 explicit affected versions
92 explicit affected versions
18 explicit affected versions
43 explicit affected versions
12 explicit affected versions
66 explicit affected versions
72 explicit affected versions
1 explicit affected versions
27 explicit affected versions
58 explicit affected versions
121 explicit affected versions
1 explicit affected versions
1 explicit affected versions
98 explicit affected versions
45 explicit affected versions
8 explicit affected versions
49 explicit affected versions
5 explicit affected versions
8 explicit affected versions
1 explicit affected versions
10 explicit affected versions
7 explicit affected versions
49 explicit affected versions
13 explicit affected versions
110 explicit affected versions
13 explicit affected versions
72 explicit affected versions
7 explicit affected versions
140 explicit affected versions
8 explicit affected versions
94 explicit affected versions
10 explicit affected versions
12 explicit affected versions
9 explicit affected versions
31 explicit affected versions
108 explicit affected versions
80 explicit affected versions
56 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
53 explicit affected versions
14 explicit affected versions
38 explicit affected versions
167 explicit affected versions
9 explicit affected versions
9 explicit affected versions
11 explicit affected versions
42 explicit affected versions
21 explicit affected versions
6 explicit affected versions
85 explicit affected versions
8 explicit affected versions
7 explicit affected versions
97 explicit affected versions
121 explicit affected versions
4 explicit affected versions
74 explicit affected versions
1 explicit affected versions
1 explicit affected versions
1 explicit affected versions
83 explicit affected versions
73 explicit affected versions
73 explicit affected versions
13 explicit affected versions
43 explicit affected versions
77 explicit affected versions
6 explicit affected versions
119 explicit affected versions
5 explicit affected versions
10 explicit affected versions
8 explicit affected versions
48 explicit affected versions
88 explicit affected versions
14 explicit affected versions
4 explicit affected versions
78 explicit affected versions
6 explicit affected versions
11 explicit affected versions
1 explicit affected versions
69 explicit affected versions
123 explicit affected versions
22 explicit affected versions
41 explicit affected versions
73 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: ksm: use range-walk function to jump over holes in scan_get_next_rmap_item Currently, scan_get_next_rmap_item() walks every page address in a VMA to locate mergeable pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions, causing ksmd to use large amount of cpu without deduplicating much pages. This patch replaces the per-address lookup with a range walk using walk_page_range(). The range walker allows KSM to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. This problem was previously discussed in [1]. Consider the following test program which creates a 32 TiB mapping in the virtual address space but only populates a single page: #include <unistd.h> #include <stdio.h> #include <sys/mman.h> /* 32 TiB */ const size_t size = 32ul * 1024 * 1024 * 1024 * 1024; int main() { char *area = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0); if (area == MAP_FAILED) { perror("mmap() failed\n"); return -1; } /* Populate a single page such that we get an anon_vma. */ *area = 0; /* Enable KSM. */ madvise(area, size, MADV_MERGEABLE); pause(); return 0; } $ ./ksm-sparse & $ echo 1 > /sys/kernel/mm/ksm/run Without this patch ksmd uses 100% of the cpu for a long time (more then 1 hour in my test machine) scanning all the 32 TiB virtual address space that contain only one mapped page. This makes ksmd essentially deadlocked not able to deduplicate anything of value. With this patch ksmd walks only the one mapped page and skips the rest of the 32 TiB virtual address space, making the scan fast using little cpu.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/f5548c318d6520d4fa3c5ed6003eeb710763cbc5
- https://git.kernel.org/stable/c/74f78421c925b6d17695566f0c5941de57fd44b3
- https://git.kernel.org/stable/c/f5548c318d6520d4fa3c5ed6003eeb710763cbc5
- https://git.kernel.org/stable/c/f62973e0767e4fcd6799087787fca08ca2a85b8c
- https://ubuntu.com/security/CVE-2025-68211
- https://ubuntu.com/security/notices/USN-8029-1
- https://ubuntu.com/security/notices/USN-8029-2
- https://ubuntu.com/security/notices/USN-8029-3
- https://ubuntu.com/security/notices/USN-8030-1
- https://ubuntu.com/security/notices/USN-8048-1
- https://ubuntu.com/security/notices/USN-8162-1
- https://ubuntu.com/security/notices/USN-8180-1
- https://ubuntu.com/security/notices/USN-8180-2
- https://ubuntu.com/security/notices/USN-8180-3
- https://ubuntu.com/security/notices/USN-8180-4
- https://ubuntu.com/security/notices/USN-8180-5
- https://ubuntu.com/security/notices/USN-8180-6
- https://ubuntu.com/security/notices/USN-8186-1
- https://ubuntu.com/security/notices/USN-8187-1
- https://ubuntu.com/security/notices/USN-8188-1
- https://ubuntu.com/security/notices/USN-8243-1
- https://ubuntu.com/security/notices/USN-8275-1
- https://ubuntu.com/security/notices/USN-8297-1
- https://www.cve.org/CVERecord?id=CVE-2025-68211