CVE-2024-45024

In the Linux kernel, the following vulnerability has been resolved:

mm/hugetlb: fix hugetlb vs. core-mm PT locking

We recently made GUP's common page table walking code to also walk hugetlb

VMAs without most hugetlb special-casing, preparing for the future of

having less hugetlb-specific page table walking code in the codebase.

Turns out that we missed one page table locking detail: page table locking

for hugetlb folios that are not mapped using a single PMD/PUD.

Assume we have hugetlb folio that spans multiple PTEs (e.g., 64 KiB

hugetlb folios on arm64 with 4 KiB base page size). GUP, as it walks the

page tables, will perform a pte_offset_map_lock() to grab the PTE table

lock.

However, hugetlb that concurrently modifies these page tables would

actually grab the mm->page_table_lock: with USE_SPLIT_PTE_PTLOCKS, the

locks would differ. Something similar can happen right now with hugetlb

folios that span multiple PMDs when USE_SPLIT_PMD_PTLOCKS.

This issue can be reproduced [1], for example triggering:

[ 3105.936100] ------------[ cut here ]------------

[ 3105.939323] WARNING: CPU: 31 PID: 2732 at mm/gup.c:142 try_grab_folio+0x11c/0x188

[ 3105.944634] Modules linked in: [...]

[ 3105.974841] CPU: 31 PID: 2732 Comm: reproducer Not tainted 6.10.0-64.eln141.aarch64 #1

[ 3105.980406] Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20240524-4.fc40 05/24/2024

[ 3105.986185] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)

[ 3105.991108] pc : try_grab_folio+0x11c/0x188

[ 3105.994013] lr : follow_page_pte+0xd8/0x430

[ 3105.996986] sp : ffff80008eafb8f0

[ 3105.999346] x29: ffff80008eafb900 x28: ffffffe8d481f380 x27: 00f80001207cff43

[ 3106.004414] x26: 0000000000000001 x25: 0000000000000000 x24: ffff80008eafba48

[ 3106.009520] x23: 0000ffff9372f000 x22: ffff7a54459e2000 x21: ffff7a546c1aa978

[ 3106.014529] x20: ffffffe8d481f3c0 x19: 0000000000610041 x18: 0000000000000001

[ 3106.019506] x17: 0000000000000001 x16: ffffffffffffffff x15: 0000000000000000

[ 3106.024494] x14: ffffb85477fdfe08 x13: 0000ffff9372ffff x12: 0000000000000000

[ 3106.029469] x11: 1fffef4a88a96be1 x10: ffff7a54454b5f0c x9 : ffffb854771b12f0

[ 3106.034324] x8 : 0008000000000000 x7 : ffff7a546c1aa980 x6 : 0008000000000080

[ 3106.038902] x5 : 00000000001207cf x4 : 0000ffff9372f000 x3 : ffffffe8d481f000

[ 3106.043420] x2 : 0000000000610041 x1 : 0000000000000001 x0 : 0000000000000000

[ 3106.047957] Call trace:

[ 3106.049522] try_grab_folio+0x11c/0x188

[ 3106.051996] follow_pmd_mask.constprop.0.isra.0+0x150/0x2e0

[ 3106.055527] follow_page_mask+0x1a0/0x2b8

[ 3106.058118] __get_user_pages+0xf0/0x348

[ 3106.060647] faultin_page_range+0xb0/0x360

[ 3106.063651] do_madvise+0x340/0x598

Let's make huge_pte_lockptr() effectively use the same PT locks as any

core-mm page table walker would. Add ptep_lockptr() to obtain the PTE

page table lock using a pte pointer -- unfortunately we cannot convert

pte_lockptr() because virt_to_page() doesn't work with kmap'ed page tables

we can have with CONFIG_HIGHPTE.

Handle CONFIG_PGTABLE_LEVELS correctly by checking in reverse order, such

that when e.g., CONFIG_PGTABLE_LEVELS==2 with

PGDIR_SIZE==P4D_SIZE==PUD_SIZE==PMD_SIZE will work as expected. Document

why that works.

There is one ugly case: powerpc 8xx, whereby we have an 8 MiB hugetlb

folio being mapped using two PTE page tables. While hugetlb wants to take

the PMD table lock, core-mm would grab the PTE table lock of one of both

PTE page tables. In such corner cases, we have to make sure that both

locks match, which is (fortunately!) currently guaranteed for 8xx as it

does not support SMP and consequently doesn't use split PT locks.

[1] https://lore.kernel.org/all/[email protected]/