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vm_struct::nr_pages is an unsigned int, and the file keeps deriving byte counts from it as nr_pages << PAGE_SHIFT. A shift is evaluated in the type of its promoted left operand, so those are 32-bit arithmetic and wrap at 4 GiB of bytes, which is 2^20 pages. Every site depends on a cast being remembered; vmap() has one, two recent commits did not. vread_iter() then computes a size of zero for a 4 GiB VM_ALLOC area and /proc/kcore returns it as zeros while reporting a successful read, which drgn, crash or gdb cannot tell from real memory, and the vrealloc() grow-in-place check declines a request that would have fit. Widen the field so the class of bug goes away instead of one site at a time. Everything feeding or consuming it widens too: vm_area_alloc_pages() and its accumulators, nr_small_pages, new_nr_pages and old_nr_pages, the index range of vm_area_free_pages(), and three page indexes that were plain int. Five casts go. Two prints needed fixing as well, %u in vmalloc_dump_obj() and %d for the unsigned field in vmalloc_info_show(). No bug report behind this, I found it reading the code. The 4 GiB wrap needs only a machine with over 4 GiB of memory. Neither larger threshold is a practical concern: 2^32 pages, where the field itself truncates, is 16 TiB and beyond what hardware can populate, and 2^31, where the plain int indexes break, is 8 TiB and larger than anything in the tree asks for. The int *nr cursor in the mapping path is unchanged and is separate work. Users outside mm/vmalloc.c need no change either. Those handing the count to a narrower parameter cannot drive it near 2^31, and kho_preserve_vmalloc() stores it into a 32-bit ABI field that still receives the same low bits; above 2^32 pages the truncation just moves out of vm_struct into that store. sizeof(struct vm_struct) on x86-64 stays 72 bytes with CONFIG_HAVE_ARCH_HUGE_VMALLOC=n and goes from 72 to 80 with it enabled, both inside the kmalloc-96 bucket it already comes from. Link: https://lore.kernel.org/20260801114915.115224-1-iprintercanon@gmail.com Fixes:0bca238046("mm/vmalloc: use physical page count in vread_iter() for VM_ALLOC areas") Fixes:d57ac904ff("mm/vmalloc: use physical page count for vrealloc() grow-in-place check") Signed-off-by: Artem Lytkin <iprintercanon@gmail.com> Suggested-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Assisted-by: Claude:claude-fable-5 Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: <shivamkalra98@zohomail.in> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst