x86/mm/pat: fix VM_PAT handling in COW mappings

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Summary

CVECVE-2024-35877
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2024-05-19 09:15:08 UTC
Updated2026-05-12 12:16:38 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: x86/mm/pat: fix VM_PAT handling in COW mappings PAT handling won't do the right thing in COW mappings: the first PTE (or, in fact, all PTEs) can be replaced during write faults to point at anon folios. Reliably recovering the correct PFN and cachemode using follow_phys() from PTEs will not work in COW mappings. Using follow_phys(), we might just get the address+protection of the anon folio (which is very wrong), or fail on swap/nonswap entries, failing follow_phys() and triggering a WARN_ON_ONCE() in untrack_pfn() and track_pfn_copy(), not properly calling free_pfn_range(). In free_pfn_range(), we either wouldn't call memtype_free() or would call it with the wrong range, possibly leaking memory. To fix that, let's update follow_phys() to refuse returning anon folios, and fallback to using the stored PFN inside vma->vm_pgoff for COW mappings if we run into that. We will now properly handle untrack_pfn() with COW mappings, where we don't need the cachemode. We'll have to fail fork()->track_pfn_copy() if the first page was replaced by an anon folio, though: we'd have to store the cachemode in the VMA to make this work, likely growing the VMA size. For now, lets keep it simple and let track_pfn_copy() just fail in that case: it would have failed in the past with swap/nonswap entries already, and it would have done the wrong thing with anon folios. Simple reproducer to trigger the WARN_ON_ONCE() in untrack_pfn(): <--- C reproducer ---> #include <stdio.h> #include <sys/mman.h> #include <unistd.h> #include <liburing.h> int main(void) { struct io_uring_params p = {}; int ring_fd; size_t size; char *map; ring_fd = io_uring_setup(1, &p); if (ring_fd < 0) { perror("io_uring_setup"); return 1; } size = p.sq_off.array + p.sq_entries * sizeof(unsigned); /* Map the submission queue ring MAP_PRIVATE */ map = mmap(0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, ring_fd, IORING_OFF_SQ_RING); if (map == MAP_FAILED) { perror("mmap"); return 1; } /* We have at least one page. Let's COW it. */ *map = 0; pause(); return 0; } <--- C reproducer ---> On a system with 16 GiB RAM and swap configured: # ./iouring & # memhog 16G # killall iouring [ 301.552930] ------------[ cut here ]------------ [ 301.553285] WARNING: CPU: 7 PID: 1402 at arch/x86/mm/pat/memtype.c:1060 untrack_pfn+0xf4/0x100 [ 301.553989] Modules linked in: binfmt_misc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_g [ 301.558232] CPU: 7 PID: 1402 Comm: iouring Not tainted 6.7.5-100.fc38.x86_64 #1 [ 301.558772] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebu4 [ 301.559569] RIP: 0010:untrack_pfn+0xf4/0x100 [ 301.559893] Code: 75 c4 eb cf 48 8b 43 10 8b a8 e8 00 00 00 3b 6b 28 74 b8 48 8b 7b 30 e8 ea 1a f7 000 [ 301.561189] RSP: 0018:ffffba2c0377fab8 EFLAGS: 00010282 [ 301.561590] RAX: 00000000ffffffea RBX: ffff9208c8ce9cc0 RCX: 000000010455e047 [ 301.562105] RDX: 07fffffff0eb1e0a RSI: 0000000000000000 RDI: ffff9208c391d200 [ 301.562628] RBP: 0000000000000000 R08: ffffba2c0377fab8 R09: 0000000000000000 [ 301.563145] R10: ffff9208d2292d50 R11: 0000000000000002 R12: 00007fea890e0000 [ 301.563669] R13: 0000000000000000 R14: ffffba2c0377fc08 R15: 0000000000000000 [ 301.564186] FS: 0000000000000000(0000) GS:ffff920c2fbc0000(0000) knlGS:0000000000000000 [ 301.564773] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 301.565197] CR2: 00007fea88ee8a20 CR3: 00000001033a8000 CR4: 0000000000750ef0 [ 301.565725] PKRU: 55555554 [ 301.565944] Call Trace: [ 301.566148] <TASK> [ 301.566325] ? untrack_pfn+0xf4/0x100 [ 301.566618] ? __warn+0x81/0x130 [ 301.566876] ? untrack_pfn+0xf4/0x100 [ 3 ---truncated---

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-401 | CWE-noinfo Not enough information

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 f18681daaec9665a15c5e7e0f591aad5d0ac622b git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 09e6bb53217bf388a0d2fd7fb21e74ab9dffc173 git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 c2b2430b48f3c9eaccd2c3d2ad75bb540d4952f4 git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 7cfee26d1950250b14c5cb0a37b142f3fcc6396a git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 97e93367e82752e475a33839a80b33bdbef1209f git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 51b7841f3fe84606ec0bd8da859d22e05e5419ec git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 1341e4b32e1fb1b0acd002ccd56f07bd32f2abc6 git Not specified
CNA Linux Linux affected 5899329b19100c0b82dc78e9b21ed8b920c9ffb3 04c35ab3bdae7fefbd7c7a7355f29fa03a035221 git Not specified
CNA Linux Linux affected 2.6.29 Not specified
CNA Linux Linux unaffected 2.6.29 semver Not specified
CNA Linux Linux unaffected 4.19.312 4.19.* semver Not specified
CNA Linux Linux unaffected 5.4.274 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.215 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.155 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.85 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.26 6.6.* semver Not specified
CNA Linux Linux unaffected 6.8.5 6.8.* semver Not specified
CNA Linux Linux unaffected 6.9 * original_commit_for_fix Not specified
ADP Siemens SIMATIC S7-1500 TM MFP - GNU/Linux Subsystem affected * custom Not specified

References

ReferenceSourceLinkTags
lists.debian.org/debian-lts-announce/2024/06/msg00017.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
cert-portal.siemens.com/productcert/html/ssa-265688.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/97e93367e82752e475a33839a80b33bdbef1209f af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/1341e4b32e1fb1b0acd002ccd56f07bd32f2abc6 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/f18681daaec9665a15c5e7e0f591aad5d0ac622b af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/51b7841f3fe84606ec0bd8da859d22e05e5419ec af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/09e6bb53217bf388a0d2fd7fb21e74ab9dffc173 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/c2b2430b48f3c9eaccd2c3d2ad75bb540d4952f4 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2024/06/msg00020.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/7cfee26d1950250b14c5cb0a37b142f3fcc6396a af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/04c35ab3bdae7fefbd7c7a7355f29fa03a035221 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
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