Message-ID: <2024102115-CVE-2024-49878-8099@gregkh>
Date: Mon, 21 Oct 2024 20:01:26 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-49878: resource: fix region_intersects() vs add_memory_driver_managed()

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

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

resource: fix region_intersects() vs add_memory_driver_managed()

On a system with CXL memory, the resource tree (/proc/iomem) related to
CXL memory may look like something as follows.

490000000-50fffffff : CXL Window 0
  490000000-50fffffff : region0
    490000000-50fffffff : dax0.0
      490000000-50fffffff : System RAM (kmem)

Because drivers/dax/kmem.c calls add_memory_driver_managed() during
onlining CXL memory, which makes "System RAM (kmem)" a descendant of "CXL
Window X".  This confuses region_intersects(), which expects all "System
RAM" resources to be at the top level of iomem_resource.  This can lead to
bugs.

For example, when the following command line is executed to write some
memory in CXL memory range via /dev/mem,

 $ dd if=data of=/dev/mem bs=$((1 << 10)) seek=$((0x490000000 >> 10)) count=1
 dd: error writing '/dev/mem': Bad address
 1+0 records in
 0+0 records out
 0 bytes copied, 0.0283507 s, 0.0 kB/s

the command fails as expected.  However, the error code is wrong.  It
should be "Operation not permitted" instead of "Bad address".  More
seriously, the /dev/mem permission checking in devmem_is_allowed() passes
incorrectly.  Although the accessing is prevented later because ioremap()
isn't allowed to map system RAM, it is a potential security issue.  During
command executing, the following warning is reported in the kernel log for
calling ioremap() on system RAM.

 ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff
 WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d
 Call Trace:
  memremap+0xcb/0x184
  xlate_dev_mem_ptr+0x25/0x2f
  write_mem+0x94/0xfb
  vfs_write+0x128/0x26d
  ksys_write+0xac/0xfe
  do_syscall_64+0x9a/0xfd
  entry_SYSCALL_64_after_hwframe+0x4b/0x53

The details of command execution process are as follows.  In the above
resource tree, "System RAM" is a descendant of "CXL Window 0" instead of a
top level resource.  So, region_intersects() will report no System RAM
resources in the CXL memory region incorrectly, because it only checks the
top level resources.  Consequently, devmem_is_allowed() will return 1
(allow access via /dev/mem) for CXL memory region incorrectly. 
Fortunately, ioremap() doesn't allow to map System RAM and reject the
access.

So, region_intersects() needs to be fixed to work correctly with the
resource tree with "System RAM" not at top level as above.  To fix it, if
we found a unmatched resource in the top level, we will continue to search
matched resources in its descendant resources.  So, we will not miss any
matched resources in resource tree anymore.

In the new implementation, an example resource tree

|------------- "CXL Window 0" ------------|
|-- "System RAM" --|

will behave similar as the following fake resource tree for
region_intersects(, IORESOURCE_SYSTEM_RAM, ),

|-- "System RAM" --||-- "CXL Window 0a" --|

Where "CXL Window 0a" is part of the original "CXL Window 0" that
isn't covered by "System RAM".

The Linux kernel CVE team has assigned CVE-2024-49878 to this issue.


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

	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 5.10.227 with commit 1d5f85f1b7db
	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 5.15.168 with commit 8a6fef7d22a1
	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 6.1.113 with commit 4b90d2eb451b
	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 6.6.55 with commit 393331e16ce2
	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 6.10.14 with commit 06ff97a20b8c
	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 6.11.3 with commit 927abc5b7d6d
	Issue introduced in 5.1 with commit c221c0b0308f and fixed in 6.12-rc1 with commit b4afe4183ec7

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-2024-49878
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:
	kernel/resource.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/1d5f85f1b7db79c75c9e07d6571ce2a7bdf725c4
	https://git.kernel.org/stable/c/8a6fef7d22a1d952aed68584d3fcc0d018d2bdc3
	https://git.kernel.org/stable/c/4b90d2eb451b357681063ba4552b10b39d7ad885
	https://git.kernel.org/stable/c/393331e16ce205e036e58b3d8ca4ee2e635f21d9
	https://git.kernel.org/stable/c/06ff97a20b8c9e9d256b0d2c3e87f78f8ccea3de
	https://git.kernel.org/stable/c/927abc5b7d6d2c2e936bec5a2f71d9512c5e72f7
	https://git.kernel.org/stable/c/b4afe4183ec77f230851ea139d91e5cf2644c68b

Powered by blists - more mailing lists