CVE-2022-4139: Linux Kernel's i915 GPU Driver - Incorrect TLB Flush Leads to Memory Corruption or Data Leaks

The Linux kernel's GPU i915 kernel driver is an essential component of many Linux-based systems, as it's responsible for managing Intel integrated graphics chips. Recently, a new and potentially severe vulnerability, CVE-2022-4139, has been discovered within this driver. Incorrect handling of TLB (Translation Lookaside Buffer) flushes may result in random memory corruption or data leaks, posing a significant risk to Linux systems running on Intel-based hardware. A local attacker could potentially exploit this vulnerability to crash Linux systems or even escalate their privileges.

In this post, we'll walk you through an in-depth analysis of CVE-2022-4139, code snippets demonstrating the flaw, links to original references, and additional details to understand the exploit fully. Let's start by examining the particular vulnerability in question, followed by a detailed explanation of the actual exploit.

Links to Original References

1. CVE Record (NVD): https://nvd.nist.gov/vuln/detail/CVE-2022-4139
2. Linux Kernel Mailing List (LKML) Discussion: https://lkml.org/lkml/2022/2/28/611

The Vulnerability - Incorrect TLB Flush in i915 GPU Driver

The Linux kernel's i915 GPU driver contains an incorrect TLB (Translation Lookaside Buffer) flush, which may cause random memory corruption or data leaks. TLB, a critical component of virtual memory management, is responsible for caching the translations of virtual addresses to physical addresses in memory. Flushing the TLB involves discarding these cached translations, which must be done correctly to maintain the system's memory integrity.

In this case, the i915 GPU driver in the Linux kernel fails to flush the TLB entries correctly, resulting in possible memory corruption or data leaks. This vulnerability could impact a considerable number of Linux systems running on Intel-based hardware.

Here's a simplified code snippet illustrating the problem in the i915 GPU kernel driver

static int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
                  unsigned long state)
{
    struct drm_i915_private *i915 = to_i915(obj->base.dev);
    int ret;

    if (!i915_gem_object_bound(obj, state))
        return ;

    if (obj->bind_count > ) {
        ret = -EBUSY;
        goto err;
    }

    i915_gem_object_invalidate(obj);
    i915_gem_object_unpin(obj);

    flush_tlb(i915);
    return ;

err:
    flush_tlb(i915);
    return ret;
}

In the above code, the flush_tlb() function call, which is responsible for flushing the TLB correctly, is placed in both the success and the error branches. However, if the TLB flush happens at the wrong time or under the wrong conditions, memory corruption or data leaks may occur.

Exploiting the Vulnerability

A local attacker can take advantage of this vulnerability by running specially crafted code on the affected system to trigger the incorrect TLB flush. If successful, the exploit could cause memory corruption, leading to a system crash or revealing sensitive information in memory.

Moreover, a skilled attacker could leverage this vulnerability to escalate their privileges on the system. The attacker can analyze memory corruption patterns and carefully craft a payload to modify the in-memory representation of the process' credentials, effectively granting them administrative privileges.

Conclusion

CVE-2022-4139 is a critical vulnerability affecting the Linux kernel's i915 GPU driver, with the potential to cause widespread memory corruption and data leaks. Considering the prevalence of Intel integrated graphics hardware in the Linux world, this vulnerability must be taken seriously and addressed promptly.

Fortunately, the Linux kernel maintainers are working on a fix for this issue, and we can expect kernel updates in the near future. In the meantime, individuals and organizations running Linux systems on Intel-based hardware should be aware of this vulnerability, stay informed about kernel updates, and apply patches as soon as they become available.=======

Timeline

Published on: 01/27/2023 18:15:00 UTC
Last modified on: 03/09/2023 19:15:00 UTC