Message-ID: <2024053042-CVE-2024-36936-3116@gregkh>
Date: Thu, 30 May 2024 17:29:28 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-36936: efi/unaccepted: touch soft lockup during memory accept

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

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

efi/unaccepted: touch soft lockup during memory accept

Commit 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused by
parallel memory acceptance") has released the spinlock so other CPUs can
do memory acceptance in parallel and not triggers softlockup on other
CPUs.

However the softlock up was intermittent shown up if the memory of the
TD guest is large, and the timeout of softlockup is set to 1 second:

 RIP: 0010:_raw_spin_unlock_irqrestore
 Call Trace:
 ? __hrtimer_run_queues
 <IRQ>
 ? hrtimer_interrupt
 ? watchdog_timer_fn
 ? __sysvec_apic_timer_interrupt
 ? __pfx_watchdog_timer_fn
 ? sysvec_apic_timer_interrupt
 </IRQ>
 ? __hrtimer_run_queues
 <TASK>
 ? hrtimer_interrupt
 ? asm_sysvec_apic_timer_interrupt
 ? _raw_spin_unlock_irqrestore
 ? __sysvec_apic_timer_interrupt
 ? sysvec_apic_timer_interrupt
 accept_memory
 try_to_accept_memory
 do_huge_pmd_anonymous_page
 get_page_from_freelist
 __handle_mm_fault
 __alloc_pages
 __folio_alloc
 ? __tdx_hypercall
 handle_mm_fault
 vma_alloc_folio
 do_user_addr_fault
 do_huge_pmd_anonymous_page
 exc_page_fault
 ? __do_huge_pmd_anonymous_page
 asm_exc_page_fault
 __handle_mm_fault

When the local irq is enabled at the end of accept_memory(), the
softlockup detects that the watchdog on single CPU has not been fed for
a while. That is to say, even other CPUs will not be blocked by
spinlock, the current CPU might be stunk with local irq disabled for a
while, which hurts not only nmi watchdog but also softlockup.

Chao Gao pointed out that the memory accept could be time costly and
there was similar report before. Thus to avoid any softlocup detection
during this stage, give the softlockup a flag to skip the timeout check
at the end of accept_memory(), by invoking touch_softlockup_watchdog().

The Linux kernel CVE team has assigned CVE-2024-36936 to this issue.


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

	Issue introduced in 6.6 with commit 50e782a86c98 and fixed in 6.8.10 with commit 781e34b73601
	Issue introduced in 6.6 with commit 50e782a86c98 and fixed in 6.9 with commit 1c5a1627f481
	Issue introduced in 6.5.9 with commit b583bfcc5a36

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-2024-36936
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:
	drivers/firmware/efi/unaccepted_memory.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/781e34b736014188ba9e46a71535237313dcda81
	https://git.kernel.org/stable/c/1c5a1627f48105cbab81d25ec2f72232bfaa8185

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