Affected: Linux

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…

Affected: Ubuntu:25.10: linux, Ubuntu:25.10: linux-raspi, Ubuntu:25.10: linux-realtime

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM64 architecture; - MIPS architecture; - Nios II architecture; - PA-RISC architecture; - RISC-V architecture; - S390 architecture; - Sun Sparc architecture; - x86 architecture; - Xtensa architecture; - Block layer subsystem; - Cryptographic API; - Compute Acceleration Framework; - ACPI drivers; - Drivers core; - Network block device driver; - Bluetooth drivers; - Bus devices; - Hardware random number generator core; - Character device driver; - Clock framework and drivers; - Data acquisition framework and drivers; - CPU frequency scaling framework; - Hardware crypto device drivers; - CXL (Compute Express Link) drivers; - Device frequency scaling framework; - ARM SCMI message protocol; - GPIO subsystem; - GPU drivers; - Hardware monitoring drivers; - HW tracing; - InfiniBand drivers; - Input Device (Miscellaneous) drivers; - IOMMU subsystem; - ISDN/mISDN subsystem; - Mailbox framework; - Multiple devices driver; - Media drivers; - Fastrpc Driver; - PCI Endpoint Test driver; - VMware Balloon Driver; - MOST (Media Oriented Systems Transport) drivers; - Network drivers; - Mellanox network drivers; - STMicroelectronics network drivers; - NVME drivers; - PCI subsystem; - Performance monitor drivers; - Pin…