Subject: CVE-2022-49001: riscv: fix race when vmap stack overflow

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

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

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

riscv: fix race when vmap stack overflow

Currently, when detecting vmap stack overflow, riscv firstly switches
to the so called shadow stack, then use this shadow stack to call the
get_overflow_stack() to get the overflow stack. However, there's
a race here if two or more harts use the same shadow stack at the same
time.

To solve this race, we introduce spin_shadow_stack atomic var, which
will be swap between its own address and 0 in atomic way, when the
var is set, it means the shadow_stack is being used; when the var
is cleared, it means the shadow_stack isn't being used.

[Palmer: Add AQ to the swap, and also some comments.]

The Linux kernel CVE team has assigned CVE-2022-49001 to this issue.

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

	Issue introduced in 5.14 with commit 31da94c25aea and fixed in 5.15.82 with commit ac00301adb19
	Issue introduced in 5.14 with commit 31da94c25aea and fixed in 6.0.12 with commit 879fabc5a954
	Issue introduced in 5.14 with commit 31da94c25aea and fixed in 6.1 with commit 7e1864332fbc

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-2022-49001
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/riscv/include/asm/asm.h
	arch/riscv/kernel/entry.S
	arch/riscv/kernel/traps.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/ac00301adb19df54f2eae1efc4bad7447c0156ce
	https://git.kernel.org/stable/c/879fabc5a95401d9bce357e4b1d24ae4a360a81f
	https://git.kernel.org/stable/c/7e1864332fbc1b993659eab7974da9fe8bf8c128