CVE-2022-50045

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

powerpc/pci: Fix get_phb_number() locking

The recent change to get_phb_number() causes a DEBUG_ATOMIC_SLEEP warning on some systems:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 1 lock held by swapper/1: #0: c157efb0 (hose_spinlock){+.+.}-{2:2}, at: pcibios_alloc_controller+0x64/0x220 Preemption disabled at: [<00000000>] 0x0 CPU: 0 PID: 1 Comm: swapper Not tainted 5.19.0-yocto-standard+ #1 Call Trace: [d101dc90] [c073b264] dump_stack_lvl+0x50/0x8c (unreliable) [d101dcb0] [c0093b70] __might_resched+0x258/0x2a8 [d101dcd0] [c0d3e634] __mutex_lock+0x6c/0x6ec [d101dd50] [c0a84174] of_alias_get_id+0x50/0xf4 [d101dd80] [c002ec78] pcibios_alloc_controller+0x1b8/0x220 [d101ddd0] [c140c9dc] pmac_pci_init+0x198/0x784 [d101de50] [c140852c] discover_phbs+0x30/0x4c [d101de60] [c0007fd4] do_one_initcall+0x94/0x344 [d101ded0] [c1403b40] kernel_init_freeable+0x1a8/0x22c [d101df10] [c00086e0] kernel_init+0x34/0x160 [d101df30] [c001b334] ret_from_kernel_thread+0x5c/0x64

This is because pcibios_alloc_controller() holds hose_spinlock but of_alias_get_id() takes of_mutex which can sleep.

The hose_spinlock protects the phb_bitmap, and also the hose_list, but it doesnt need to be held while get_phb_number() calls the OF routines, because those are only looking up information in the device tree.

So fix it by having get_phb_number() take the hose_spinlock itself, only where required, and then dropping the lock before returning. pcibios_alloc_controller() then needs to take the lock again before the list_add() but thats safe, the order of the list is not important.

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/1d9e75c3d8cdf7c96a94cb77450d4ee070279e6a
• https://git.kernel.org/stable/c/5db5ce0f1963c6c8275719a80cb65e9c98d32726
• https://git.kernel.org/stable/c/6f75057c21eab12c6ccb7f06f859641a6edfab99
• https://git.kernel.org/stable/c/8d48562a2729742f767b0fdd994d6b2a56a49c63
• https://git.kernel.org/stable/c/90f195c01a2e8d8da6281791617e21109719c981
• https://git.kernel.org/stable/c/a868f771ee41c97a25a04b8c632a7f06689b307b
• https://git.kernel.org/stable/c/ccb0a42d3f40c436295e0fef57ab613ae5b925a4