Subject: CVE-2024-26745: powerpc/pseries/iommu: IOMMU table is not initialized for kdump over SR-IOV

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

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

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

powerpc/pseries/iommu: IOMMU table is not initialized for kdump over SR-IOV

When kdump kernel tries to copy dump data over SR-IOV, LPAR panics due
to NULL pointer exception:

  Kernel attempted to read user page (0) - exploit attempt? (uid: 0)
  BUG: Kernel NULL pointer dereference on read at 0x00000000
  Faulting instruction address: 0xc000000020847ad4
  Oops: Kernel access of bad area, sig: 11 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
  Modules linked in: mlx5_core(+) vmx_crypto pseries_wdt papr_scm libnvdimm mlxfw tls psample sunrpc fuse overlay squashfs loop
  CPU: 12 PID: 315 Comm: systemd-udevd Not tainted 6.4.0-Test102+ #12
  Hardware name: IBM,9080-HEX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1060.00 (NH1060_008) hv:phyp pSeries
  NIP:  c000000020847ad4 LR: c00000002083b2dc CTR: 00000000006cd18c
  REGS: c000000029162ca0 TRAP: 0300   Not tainted  (6.4.0-Test102+)
  MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 48288244  XER: 00000008
  CFAR: c00000002083b2d8 DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 1
  ...
  NIP _find_next_zero_bit+0x24/0x110
  LR  bitmap_find_next_zero_area_off+0x5c/0xe0
  Call Trace:
    dev_printk_emit+0x38/0x48 (unreliable)
    iommu_area_alloc+0xc4/0x180
    iommu_range_alloc+0x1e8/0x580
    iommu_alloc+0x60/0x130
    iommu_alloc_coherent+0x158/0x2b0
    dma_iommu_alloc_coherent+0x3c/0x50
    dma_alloc_attrs+0x170/0x1f0
    mlx5_cmd_init+0xc0/0x760 [mlx5_core]
    mlx5_function_setup+0xf0/0x510 [mlx5_core]
    mlx5_init_one+0x84/0x210 [mlx5_core]
    probe_one+0x118/0x2c0 [mlx5_core]
    local_pci_probe+0x68/0x110
    pci_call_probe+0x68/0x200
    pci_device_probe+0xbc/0x1a0
    really_probe+0x104/0x540
    __driver_probe_device+0xb4/0x230
    driver_probe_device+0x54/0x130
    __driver_attach+0x158/0x2b0
    bus_for_each_dev+0xa8/0x130
    driver_attach+0x34/0x50
    bus_add_driver+0x16c/0x300
    driver_register+0xa4/0x1b0
    __pci_register_driver+0x68/0x80
    mlx5_init+0xb8/0x100 [mlx5_core]
    do_one_initcall+0x60/0x300
    do_init_module+0x7c/0x2b0

At the time of LPAR dump, before kexec hands over control to kdump
kernel, DDWs (Dynamic DMA Windows) are scanned and added to the FDT.
For the SR-IOV case, default DMA window "ibm,dma-window" is removed from
the FDT and DDW added, for the device.

Now, kexec hands over control to the kdump kernel.

When the kdump kernel initializes, PCI busses are scanned and IOMMU
group/tables created, in pci_dma_bus_setup_pSeriesLP(). For the SR-IOV
case, there is no "ibm,dma-window". The original commit: b1fc44eaa9ba,
fixes the path where memory is pre-mapped (direct mapped) to the DDW.
When TCEs are direct mapped, there is no need to initialize IOMMU
tables.

iommu_table_setparms_lpar() only considers "ibm,dma-window" property
when initiallizing IOMMU table. In the scenario where TCEs are
dynamically allocated for SR-IOV, newly created IOMMU table is not
initialized. Later, when the device driver tries to enter TCEs for the
SR-IOV device, NULL pointer execption is thrown from iommu_area_alloc().

The fix is to initialize the IOMMU table with DDW property stored in the
FDT. There are 2 points to remember:

	1. For the dedicated adapter, kdump kernel would encounter both
	   default and DDW in FDT. In this case, DDW property is used to
	   initialize the IOMMU table.

	2. A DDW could be direct or dynamic mapped. kdump kernel would
	   initialize IOMMU table and mark the existing DDW as
	   "dynamic". This works fine since, at the time of table
	   initialization, iommu_table_clear() makes some space in the
	   DDW, for some predefined number of TCEs which are needed for
	   kdump to succeed.

The Linux kernel CVE team has assigned CVE-2024-26745 to this issue.

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

	Issue introduced in 6.0 with commit b1fc44eaa9ba and fixed in 6.1.81 with commit 7eb95e0af5c9
	Issue introduced in 6.0 with commit b1fc44eaa9ba and fixed in 6.6.21 with commit d4d1e4b1513d
	Issue introduced in 6.0 with commit b1fc44eaa9ba and fixed in 6.7.9 with commit 5da6d306f315
	Issue introduced in 6.0 with commit b1fc44eaa9ba and fixed in 6.8 with commit 09a3c1e46142
	Issue introduced in 5.18.18 with commit b9f08b2649dd
	Issue introduced in 5.19.2 with commit 58942f672c6d

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-2024-26745
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/platforms/pseries/iommu.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/7eb95e0af5c9c2e6fad50356eaf32d216d0e7bc3
	https://git.kernel.org/stable/c/d4d1e4b1513d975961de7bb4f75e450a92d65ebf
	https://git.kernel.org/stable/c/5da6d306f315344af1ca2eff4bd9b10b130f0c28
	https://git.kernel.org/stable/c/09a3c1e46142199adcee372a420b024b4fc61051