Date: Mon, 28 Aug 2017 14:34:41 -0700 From: Kees Cook <keescook@...omium.org> To: linux-kernel@...r.kernel.org Cc: Kees Cook <keescook@...omium.org>, linux-mm@...ck.org, kernel-hardening@...ts.openwall.com, David Windsor <dave@...lcore.net> Subject: [PATCH v2 00/30] Hardened usercopy whitelisting This series is modified from Brad Spengler/PaX Team's PAX_USERCOPY code in the last public patch of grsecurity/PaX based on our understanding of the code. Changes or omissions from the original code are ours and don't reflect the original grsecurity/PaX code. David Windsor did the bulk of the porting, refactoring, splitting, testing, etc; I just did some extra tweaks, hunk moving, traces, and extra patches. Description from patch 1: Currently, hardened usercopy performs dynamic bounds checking on slab cache objects. This is good, but still leaves a lot of kernel memory available to be copied to/from userspace in the face of bugs. To further restrict what memory is available for copying, this creates a way to whitelist specific areas of a given slab cache object for copying to/from userspace, allowing much finer granularity of access control. Slab caches that are never exposed to userspace can declare no whitelist for their objects, thereby keeping them unavailable to userspace via dynamic copy operations. (Note, an implicit form of whitelisting is the use of constant sizes in usercopy operations and get_user()/put_user(); these bypass hardened usercopy checks since these sizes cannot change at runtime.) To support this whitelist annotation, usercopy region offset and size members are added to struct kmem_cache. The slab allocator receives a new function, kmem_cache_create_usercopy(), that creates a new cache with a usercopy region defined, suitable for declaring spans of fields within the objects that get copied to/from userspace. In this patch, the default kmem_cache_create() marks the entire allocation as whitelisted, leaving it semantically unchanged. Once all fine-grained whitelists have been added (in subsequent patches), this will be changed to a usersize of 0, making caches created with kmem_cache_create() not copyable to/from userspace. After the entire usercopy whitelist series is applied, less than 15% of the slab cache memory remains exposed to potential usercopy bugs after a fresh boot: Total Slab Memory: 48074720 Usercopyable Memory: 6367532 13.2% task_struct 0.2% 4480/1630720 RAW 0.3% 300/96000 RAWv6 2.1% 1408/64768 ext4_inode_cache 3.0% 269760/8740224 dentry 11.1% 585984/5273856 mm_struct 29.1% 54912/188448 kmalloc-8 100.0% 24576/24576 kmalloc-16 100.0% 28672/28672 kmalloc-32 100.0% 81920/81920 kmalloc-192 100.0% 96768/96768 kmalloc-128 100.0% 143360/143360 names_cache 100.0% 163840/163840 kmalloc-64 100.0% 167936/167936 kmalloc-256 100.0% 339968/339968 kmalloc-512 100.0% 350720/350720 kmalloc-96 100.0% 455616/455616 kmalloc-8192 100.0% 655360/655360 kmalloc-1024 100.0% 812032/812032 kmalloc-4096 100.0% 819200/819200 kmalloc-2048 100.0% 1310720/1310720 After some kernel build workloads, the percentage (mainly driven by dentry and inode caches expanding) drops under 10%: Total Slab Memory: 95516184 Usercopyable Memory: 8497452 8.8% task_struct 0.2% 4000/1456000 RAW 0.3% 300/96000 RAWv6 2.1% 1408/64768 ext4_inode_cache 3.0% 1217280/39439872 dentry 11.1% 1623200/14608800 mm_struct 29.1% 73216/251264 kmalloc-8 100.0% 24576/24576 kmalloc-16 100.0% 28672/28672 kmalloc-32 100.0% 94208/94208 kmalloc-192 100.0% 96768/96768 kmalloc-128 100.0% 143360/143360 names_cache 100.0% 163840/163840 kmalloc-64 100.0% 245760/245760 kmalloc-256 100.0% 339968/339968 kmalloc-512 100.0% 350720/350720 kmalloc-96 100.0% 563520/563520 kmalloc-8192 100.0% 655360/655360 kmalloc-1024 100.0% 794624/794624 kmalloc-4096 100.0% 819200/819200 kmalloc-2048 100.0% 1257472/1257472 ------ The patches are broken in several stages of changes: Prepare and whitelist kmalloc: [PATCH 01/30] usercopy: Prepare for usercopy whitelisting [PATCH 02/30] usercopy: Enforce slab cache usercopy region boundaries [PATCH 03/30] usercopy: Mark kmalloc caches as usercopy caches Update VFS layer for symlinks and other inline storage: [PATCH 04/30] dcache: Define usercopy region in dentry_cache slab [PATCH 05/30] vfs: Define usercopy region in names_cache slab caches [PATCH 06/30] vfs: Copy struct mount.mnt_id to userspace using [PATCH 07/30] ext4: Define usercopy region in ext4_inode_cache slab [PATCH 08/30] ext2: Define usercopy region in ext2_inode_cache slab [PATCH 09/30] jfs: Define usercopy region in jfs_ip slab cache [PATCH 10/30] befs: Define usercopy region in befs_inode_cache slab [PATCH 11/30] exofs: Define usercopy region in exofs_inode_cache slab [PATCH 12/30] orangefs: Define usercopy region in [PATCH 13/30] ufs: Define usercopy region in ufs_inode_cache slab [PATCH 14/30] vxfs: Define usercopy region in vxfs_inode slab cache [PATCH 15/30] xfs: Define usercopy region in xfs_inode slab cache [PATCH 16/30] cifs: Define usercopy region in cifs_request slab cache Update scsi layer for inline storage: [PATCH 17/30] scsi: Define usercopy region in scsi_sense_cache slab Whitelist a few network protocol-specific areas of memory: [PATCH 18/30] net: Define usercopy region in struct proto slab cache [PATCH 19/30] ip: Define usercopy region in IP proto slab cache [PATCH 20/30] caif: Define usercopy region in caif proto slab cache [PATCH 21/30] sctp: Define usercopy region in SCTP proto slab cache [PATCH 22/30] sctp: Copy struct sctp_sock.autoclose to userspace [PATCH 23/30] net: Restrict unwhitelisted proto caches to size 0 Whitelist areas of process memory: [PATCH 24/30] fork: Define usercopy region in mm_struct slab caches [PATCH 25/30] fork: Define usercopy region in thread_stack slab Deal with per-architecture thread_struct whitelisting: [PATCH 26/30] fork: Provide usercopy whitelisting for task_struct [PATCH 27/30] x86: Implement thread_struct whitelist for hardened [PATCH 28/30] arm64: Implement thread_struct whitelist for hardened [PATCH 29/30] arm: Implement thread_struct whitelist for hardened Make blacklisting the default: [PATCH 30/30] usercopy: Restrict non-usercopy caches to size 0 v2: - added tracing of allocation and usage - refactored solutions for task_struct - split up network patches for readability I intend for this to land via my usercopy hardening tree, so Acks, Reviewed, and Tested-bys would be greatly appreciated. I have some questions in a few patches (e.g. CIFS and thread_stack) that would be nice to get answered for completeness. FWIW, this series has survived over the weekend in 0-day testing. Thanks! -Kees (and David)
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