Subject: CVE-2022-48762: arm64: extable: fix load_unaligned_zeropad() reg indices

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

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

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

arm64: extable: fix load_unaligned_zeropad() reg indices

In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
addr register indices from ex->type rather than ex->data. As ex->type will
contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
 * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
   extracted from bits [9:5]. Thus, we may attempt to dereference an
   arbitrary address as X0 may hold an arbitrary value.
 * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
   extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
   behaviour within load_unaligned_zeropad() and its caller.

Fix this by extracting both values from ex->data as originally intended.

On an MTE-enabled QEMU image we are hitting the following crash:
 Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
 Call trace:
  fixup_exception+0xc4/0x108
  __do_kernel_fault+0x3c/0x268
  do_tag_check_fault+0x3c/0x104
  do_mem_abort+0x44/0xf4
  el1_abort+0x40/0x64
  el1h_64_sync_handler+0x60/0xa0
  el1h_64_sync+0x7c/0x80
  link_path_walk+0x150/0x344
  path_openat+0xa0/0x7dc
  do_filp_open+0xb8/0x168
  do_sys_openat2+0x88/0x17c
  __arm64_sys_openat+0x74/0xa0
  invoke_syscall+0x48/0x148
  el0_svc_common+0xb8/0xf8
  do_el0_svc+0x28/0x88
  el0_svc+0x24/0x84
  el0t_64_sync_handler+0x88/0xec
  el0t_64_sync+0x1b4/0x1b8
 Code: f8695a69 71007d1f 540000e0 927df12a (f940014a)

The Linux kernel CVE team has assigned CVE-2022-48762 to this issue.

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

	Issue introduced in 5.16 with commit 753b32368705 and fixed in 5.16.5 with commit 47fe7a1c5e3e
	Issue introduced in 5.16 with commit 753b32368705 and fixed in 5.17 with commit 3758a6c74e08

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-2022-48762
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/arm64/mm/extable.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/47fe7a1c5e3e011eeb4ab79f2d54a794fdd1c3eb
	https://git.kernel.org/stable/c/3758a6c74e08bdc15ccccd6872a6ad37d165239a