CVE-2026-93180: drm/panthor: Fix NPD issue on partial unmap of an evicted BO

CVE-2026-93180: drm/panthor: Fix NPD issue on partial unmap of an evicted BO

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

drm/panthor: Fix NPD issue on partial unmap of an evicted BO

This commit fixes the NULL pointer dereference issue that would have
happened on the split of GPU mapping due to partial unmap of an evicted
BO. There is a logic to handle the partial unmap of huge pages when the
GPU mapping is split. That logic was not being completely skipped for
the VMA of an evicted BO and that resulted in a NPD possibility for the
'bo->backing.pages' pointer, which is set to NULL when pages of a
BO are released on eviction.

Following dump was seen when a partial unmap was exercised for an
evicted BO.
Unable to handle kernel paging request at virtual address 0000000000002000
Mem abort info:
  ESR = 0x0000000096000004
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x04: level 0 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=00000008842e8000
[0000000000002000] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 0000000096000004 [#1]  SMP
<snip>
pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : iova_mapped_as_huge_page+0x20/0x68 [panthor]
lr : panthor_gpuva_sm_step_remap+0x39c/0x498 [panthor]
sp : ffff800086193920
x29: ffff800086193920 x28: ffff800086193a18 x27: ffff800086193b80
x26: 0000000000400000 x25: 0000000000810000 x24: 0000000000400000
x23: ffff000808af1800 x22: 0000000000a00000 x21: ffff800086193a00
x20: ffff000806fd3f00 x19: 0000000000410000 x18: 00000000ffffffff
x17: 0000000000000000 x16: 0000000000000000 x15: ffff800083ce2d83
x14: 0000000000000000 x13: 3120646574636976 x12: 6520303030303138
x11: 2d30303030313420 x10: ffff8000836e6c80 x9 : ffff80007bfc889c
x8 : 3fffffffffffefff x7 : ffff8000836e6c80 x6 : 0000000000000000
x5 : ffff00097ef19088 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 0000000000010000 x1 : 0000000000000400 x0 : 0000000000000000
Call trace:
 iova_mapped_as_huge_page+0x20/0x68 [panthor] (P)
 op_remap_cb.isra.0+0x70/0xb0
 __drm_gpuvm_sm_unmap+0xf8/0x1c0
 drm_gpuvm_sm_unmap+0x40/0x60
 panthor_vm_exec_op+0xa0/0x168 [panthor]
 panthor_vm_bind_exec_sync_op+0x8c/0xb8 [panthor]
 panthor_ioctl_vm_bind+0xbc/0x170 [panthor]
 drm_ioctl_kernel+0xc0/0x140
 drm_ioctl+0x20c/0x500
 __arm64_sys_ioctl+0xb4/0x118
 invoke_syscall+0x5c/0x120
 el0_svc_common.constprop.0+0x48/0xf8
 do_el0_svc+0x28/0x40
 el0_svc+0x38/0x128
 el0t_64_sync_handler+0xa0/0xe8
 el0t_64_sync+0x198/0x1a0
Code: 8b030021 cb020021 f940b800 d34cfc21 (f8617801)
---[ end trace 0000000000000000 ]---

v2: Fix indentation

The Linux kernel CVE team has assigned CVE-2026-93180 to this issue.


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

	Issue introduced in 7.0 with commit 8e7460eac786c72f48c4e04ce9be692b939428ce and fixed in 7.2.6 with commit 23d41b2e68765ad7095b1424f70c21c281f8a600
	Issue introduced in 7.0 with commit 8e7460eac786c72f48c4e04ce9be692b939428ce and fixed in 7.3-rc1 with commit 5fb40edc7439b99d001988da63485ca51dbd3550

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-2026-93180
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:
	drivers/gpu/drm/panthor/panthor_mmu.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/23d41b2e68765ad7095b1424f70c21c281f8a600
	https://git.kernel.org/stable/c/5fb40edc7439b99d001988da63485ca51dbd3550