Subject: CVE-2024-41070: KVM: PPC: Book3S HV: Prevent UAF in kvm_spapr_tce_attach_iommu_group()

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

KVM: PPC: Book3S HV: Prevent UAF in kvm_spapr_tce_attach_iommu_group()

Al reported a possible use-after-free (UAF) in kvm_spapr_tce_attach_iommu_group().

It looks up `stt` from tablefd, but then continues to use it after doing
fdput() on the returned fd. After the fdput() the tablefd is free to be
closed by another thread. The close calls kvm_spapr_tce_release() and
then release_spapr_tce_table() (via call_rcu()) which frees `stt`.

Although there are calls to rcu_read_lock() in
kvm_spapr_tce_attach_iommu_group() they are not sufficient to prevent
the UAF, because `stt` is used outside the locked regions.

With an artifcial delay after the fdput() and a userspace program which
triggers the race, KASAN detects the UAF:

  BUG: KASAN: slab-use-after-free in kvm_spapr_tce_attach_iommu_group+0x298/0x720 [kvm]
  Read of size 4 at addr c000200027552c30 by task kvm-vfio/2505
  CPU: 54 PID: 2505 Comm: kvm-vfio Not tainted 6.10.0-rc3-next-20240612-dirty #1
  Hardware name: 8335-GTH POWER9 0x4e1202 opal:skiboot-v6.5.3-35-g1851b2a06 PowerNV
  Call Trace:
    dump_stack_lvl+0xb4/0x108 (unreliable)
    print_report+0x2b4/0x6ec
    kasan_report+0x118/0x2b0
    __asan_load4+0xb8/0xd0
    kvm_spapr_tce_attach_iommu_group+0x298/0x720 [kvm]
    kvm_vfio_set_attr+0x524/0xac0 [kvm]
    kvm_device_ioctl+0x144/0x240 [kvm]
    sys_ioctl+0x62c/0x1810
    system_call_exception+0x190/0x440
    system_call_vectored_common+0x15c/0x2ec
  ...
  Freed by task 0:
   ...
   kfree+0xec/0x3e0
   release_spapr_tce_table+0xd4/0x11c [kvm]
   rcu_core+0x568/0x16a0
   handle_softirqs+0x23c/0x920
   do_softirq_own_stack+0x6c/0x90
   do_softirq_own_stack+0x58/0x90
   __irq_exit_rcu+0x218/0x2d0
   irq_exit+0x30/0x80
   arch_local_irq_restore+0x128/0x230
   arch_local_irq_enable+0x1c/0x30
   cpuidle_enter_state+0x134/0x5cc
   cpuidle_enter+0x6c/0xb0
   call_cpuidle+0x7c/0x100
   do_idle+0x394/0x410
   cpu_startup_entry+0x60/0x70
   start_secondary+0x3fc/0x410
   start_secondary_prolog+0x10/0x14

Fix it by delaying the fdput() until `stt` is no longer in use, which
is effectively the entire function. To keep the patch minimal add a call
to fdput() at each of the existing return paths. Future work can convert
the function to goto or __cleanup style cleanup.

With the fix in place the test case no longer triggers the UAF.

The Linux kernel CVE team has assigned CVE-2024-41070 to this issue.

Affected and fixed versions
===========================

	Fixed in 5.4.281 with commit be847bb20c80
	Fixed in 5.10.223 with commit 4cdf6926f443
	Fixed in 5.15.164 with commit b26c8c85463e
	Fixed in 6.1.101 with commit 5f856023971f
	Fixed in 6.6.42 with commit 82c7a4cf14aa
	Fixed in 6.9.11 with commit 9975f93c760a
	Fixed in 6.10 with commit a986fa57fd81

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-41070
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	arch/powerpc/kvm/book3s_64_vio.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/be847bb20c809de8ac124431b556f244400b0491
	https://git.kernel.org/stable/c/4cdf6926f443c84f680213c7aafbe6f91a5fcbc0
	https://git.kernel.org/stable/c/b26c8c85463ef27a522d24fcd05651f0bb039e47
	https://git.kernel.org/stable/c/5f856023971f97fff74cfaf21b48ec320147b50a
	https://git.kernel.org/stable/c/82c7a4cf14aa866f8f7f09e662b02eddc49ee0bf
	https://git.kernel.org/stable/c/9975f93c760a32453d7639cf6fcf3f73b4e71ffe
	https://git.kernel.org/stable/c/a986fa57fd81a1430e00b3c6cf8a325d6f894a63