cve/published/2022/CVE-2022-49214.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2022-49214: powerpc/64s: Don't use DSISR for SLB faults

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

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

powerpc/64s: Don't use DSISR for SLB faults

Since commit 46ddcb3950a2 ("powerpc/mm: Show if a bad page fault on data
is read or write.") we use page_fault_is_write(regs->dsisr) in
__bad_page_fault() to determine if the fault is for a read or write, and
change the message printed accordingly.

But SLB faults, aka Data Segment Interrupts, don't set DSISR (Data
Storage Interrupt Status Register) to a useful value. All ISA versions
from v2.03 through v3.1 specify that the Data Segment Interrupt sets
DSISR "to an undefined value". As far as I can see there's no mention of
SLB faults setting DSISR in any BookIV content either.

This manifests as accesses that should be a read being incorrectly
reported as writes, for example, using the xmon "dump" command:

  0:mon> d 0x5deadbeef0000000
  5deadbeef0000000
  [359526.415354][    C6] BUG: Unable to handle kernel data access on write at 0x5deadbeef0000000
  [359526.415611][    C6] Faulting instruction address: 0xc00000000010a300
  cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf400]
      pc: c00000000010a300: mread+0x90/0x190

If we disassemble the PC, we see a load instruction:

  0:mon> di c00000000010a300
  c00000000010a300 89490000      lbz     r10,0(r9)

We can also see in exceptions-64s.S that the data_access_slb block
doesn't set IDSISR=1, which means it doesn't load DSISR into pt_regs. So
the value we're using to determine if the fault is a read/write is some
stale value in pt_regs from a previous page fault.

Rework the printing logic to separate the SLB fault case out, and only
print read/write in the cases where we can determine it.

The result looks like eg:

  0:mon> d 0x5deadbeef0000000
  5deadbeef0000000
  [  721.779525][    C6] BUG: Unable to handle kernel data access at 0x5deadbeef0000000
  [  721.779697][    C6] Faulting instruction address: 0xc00000000014cbe0
  cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf390]

  0:mon> d 0
  0000000000000000
  [  742.793242][    C6] BUG: Kernel NULL pointer dereference at 0x00000000
  [  742.793316][    C6] Faulting instruction address: 0xc00000000014cbe0
  cpu 0x6: Vector: 380 (Data SLB Access) at [c00000000ffbf390]

The Linux kernel CVE team has assigned CVE-2022-49214 to this issue.


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

	Issue introduced in 5.5 with commit 46ddcb3950a28c0df4815e8dbb8d4b91d5d9f22d and fixed in 5.15.33 with commit 4a852ff9b7bea9c640540e2c1bc70bd3ba455d61
	Issue introduced in 5.5 with commit 46ddcb3950a28c0df4815e8dbb8d4b91d5d9f22d and fixed in 5.16.19 with commit a3dae36d632b2cf6eb20314273e512a96cb43c9a
	Issue introduced in 5.5 with commit 46ddcb3950a28c0df4815e8dbb8d4b91d5d9f22d and fixed in 5.17.2 with commit 093449bb182db885dae816d62874cccab7a4c42a
	Issue introduced in 5.5 with commit 46ddcb3950a28c0df4815e8dbb8d4b91d5d9f22d and fixed in 5.18 with commit d4679ac8ea2e5078704aa1c026db36580cc1bf9a

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-2022-49214
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/mm/fault.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/4a852ff9b7bea9c640540e2c1bc70bd3ba455d61
	https://git.kernel.org/stable/c/a3dae36d632b2cf6eb20314273e512a96cb43c9a
	https://git.kernel.org/stable/c/093449bb182db885dae816d62874cccab7a4c42a
	https://git.kernel.org/stable/c/d4679ac8ea2e5078704aa1c026db36580cc1bf9a