Goal Reached Thanks to every supporter — we hit 100%!

Goal: 1000 CNY · Raised: 1359 CNY

100%
Buy Us a Coffee

CVE-2021-4440— x86/xen: Drop USERGS_SYSRET64 paravirt call

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于x86/xen USERGS_SYSRET64中存在安全问题。

AI Predicted 5.3 Difficulty: Trivial EPSS 0.22% · P12

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 2

VendorProduct Version RangeStatus
Linux Linux cea750c99d8f6391080c420f811a46b21bad7cf4< 1424ab4bb386df9cc590c73afa55f13e9b00dea2 affected
5.10.215< 5.10.218 affected
Get alerts for future matching vulnerabilities Log in to subscribe

I. Basic Information for CVE-2021-4440

Vulnerability Information
Have questions about the vulnerability? See if Shenlong's analysis helps!
View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title
x86/xen: Drop USERGS_SYSRET64 paravirt call
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: x86/xen: Drop USERGS_SYSRET64 paravirt call commit afd30525a659ac0ae0904f0cb4a2ca75522c3123 upstream. USERGS_SYSRET64 is used to return from a syscall via SYSRET, but a Xen PV guest will nevertheless use the IRET hypercall, as there is no sysret PV hypercall defined. So instead of testing all the prerequisites for doing a sysret and then mangling the stack for Xen PV again for doing an iret just use the iret exit from the beginning. This can easily be done via an ALTERNATIVE like it is done for the sysenter compat case already. It should be noted that this drops the optimization in Xen for not restoring a few registers when returning to user mode, but it seems as if the saved instructions in the kernel more than compensate for this drop (a kernel build in a Xen PV guest was slightly faster with this patch applied). While at it remove the stale sysret32 remnants. [ pawan: Brad Spengler and Salvatore Bonaccorso <carnil@debian.org> reported a problem with the 5.10 backport commit edc702b4a820 ("x86/entry_64: Add VERW just before userspace transition"). When CONFIG_PARAVIRT_XXL=y, CLEAR_CPU_BUFFERS is not executed in syscall_return_via_sysret path as USERGS_SYSRET64 is runtime patched to: .cpu_usergs_sysret64 = { 0x0f, 0x01, 0xf8, 0x48, 0x0f, 0x07 }, // swapgs; sysretq which is missing CLEAR_CPU_BUFFERS. It turns out dropping USERGS_SYSRET64 simplifies the code, allowing CLEAR_CPU_BUFFERS to be explicitly added to syscall_return_via_sysret path. Below is with CONFIG_PARAVIRT_XXL=y and this patch applied: syscall_return_via_sysret: ... <+342>: swapgs <+345>: xchg %ax,%ax <+347>: verw -0x1a2(%rip) <------ <+354>: sysretq ]
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于x86/xen USERGS_SYSRET64中存在安全问题。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux cea750c99d8f6391080c420f811a46b21bad7cf4 ~ 1424ab4bb386df9cc590c73afa55f13e9b00dea2 -
Linux Linux 5.10.215 ~ 5.10.218 -

II. Public POCs for CVE-2021-4440

# POC Description Source Link Shenlong Link
AI-Generated POC Premium

No public POC found.

Login to generate AI POC

III. Intelligence Information for CVE-2021-4440

请登录查看更多情报信息。

Other References for CVE-2021-4440 (2)

Same Patch Batch · Linux · 2024-06-25 · 24 CVEs total

CVE-2024-39293 9.8 CRITICAL Revert "xsk: Support redirect to any socket bound to the same umem"
CVE-2024-37354 7.8 HIGH btrfs: fix crash on racing fsync and size-extending write into prealloc
CVE-2024-39471 7.8 HIGH drm/amdgpu: add error handle to avoid out-of-bounds
CVE-2024-39467 7.8 HIGH f2fs: fix to do sanity check on i_xattr_nid in sanity_check_inode()
CVE-2024-39463 7.8 HIGH 9p: add missing locking around taking dentry fid list
CVE-2024-38385 7.8 HIGH genirq/irqdesc: Prevent use-after-free in irq_find_at_or_after()
CVE-2024-37078 7.8 HIGH nilfs2: fix potential kernel bug due to lack of writeback flag waiting
CVE-2024-38306 7.8 HIGH btrfs: protect folio::private when attaching extent buffer folios
CVE-2024-39468 7.5 HIGH smb: client: fix deadlock in smb2_find_smb_tcon()
CVE-2024-39469 7.1 HIGH nilfs2: fix nilfs_empty_dir() misjudgment and long loop on I/O errors
CVE-2022-48772 media: lgdt3306a: Add a check against null-pointer-def
CVE-2024-38661 s390/ap: Fix crash in AP internal function modify_bitmap()
CVE-2024-39470 eventfs: Fix a possible null pointer dereference in eventfs_find_events()
CVE-2024-39466 thermal/drivers/qcom/lmh: Check for SCM availability at probe
CVE-2024-39464 media: v4l: async: Fix notifier list entry init
CVE-2024-39465 media: mgb4: Fix double debugfs remove
CVE-2024-39462 clk: bcm: dvp: Assign ->num before accessing ->hws
CVE-2024-39461 clk: bcm: rpi: Assign ->num before accessing ->hws
CVE-2024-39371 io_uring: check for non-NULL file pointer in io_file_can_poll()
CVE-2024-39301 net/9p: fix uninit-value in p9_client_rpc()

Showing top 20 of 24 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2021-4440

No comments yet

Leave a comment