Message-ID: <2025022611-CVE-2022-49164-12d7@gregkh>
Date: Wed, 26 Feb 2025 02:56:09 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2022-49164: powerpc/tm: Fix more userspace r13 corruption

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

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

powerpc/tm: Fix more userspace r13 corruption

Commit cf13435b730a ("powerpc/tm: Fix userspace r13 corruption") fixes a
problem in treclaim where a SLB miss can occur on the
thread_struct->ckpt_regs while SCRATCH0 is live with the saved user r13
value, clobbering it with the kernel r13 and ultimately resulting in
kernel r13 being stored in ckpt_regs.

There is an equivalent problem in trechkpt where the user r13 value is
loaded into r13 from chkpt_regs to be recheckpointed, but a SLB miss
could occur on ckpt_regs accesses after that, which will result in r13
being clobbered with a kernel value and that will get recheckpointed and
then restored to user registers.

The same memory page is accessed right before this critical window where
a SLB miss could cause corruption, so hitting the bug requires the SLB
entry be removed within a small window of instructions, which is
possible if a SLB related MCE hits there. PAPR also permits the
hypervisor to discard this SLB entry (because slb_shadow->persistent is
only set to SLB_NUM_BOLTED) although it's not known whether any
implementations would do this (KVM does not). So this is an extremely
unlikely bug, only found by inspection.

Fix this by also storing user r13 in a temporary location on the kernel
stack and don't change the r13 register from kernel r13 until the RI=0
critical section that does not fault.

The SCRATCH0 change is not strictly part of the fix, it's only used in
the RI=0 section so it does not have the same problem as the previous
SCRATCH0 bug.

The Linux kernel CVE team has assigned CVE-2022-49164 to this issue.


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

	Issue introduced in 3.9 with commit 98ae22e15b430bfed5def01ac1a88ec9396284c8 and fixed in 5.15.54 with commit 5dce84f475d13b773a1a4c823581cab25044d86a
	Issue introduced in 3.9 with commit 98ae22e15b430bfed5def01ac1a88ec9396284c8 and fixed in 5.17.2 with commit 73d8082c90f17dfba57cad4ca94db5cae323f1b1
	Issue introduced in 3.9 with commit 98ae22e15b430bfed5def01ac1a88ec9396284c8 and fixed in 5.18 with commit 9d71165d3934e607070c4e48458c0cf161b1baea

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-2022-49164
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/kernel/tm.S


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/5dce84f475d13b773a1a4c823581cab25044d86a
	https://git.kernel.org/stable/c/73d8082c90f17dfba57cad4ca94db5cae323f1b1
	https://git.kernel.org/stable/c/9d71165d3934e607070c4e48458c0cf161b1baea

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