CVE-2026-63878 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: check num_entries in GEM_OP GET_MAPPING_INFO
kvcalloc(args->num_entries, sizeof(*vm_entries), GFP_KERNEL) at amdgpu_gem.c:1050 uses the user-supplied num_entries directly without any upper bounds check. Since num_entries is a __u32 and sizeof(drm_amdgpu_gem_vm_entry) is 32 bytes, a large num_entries produces an allocation exceeding INT_MAX, triggering WARNING in __kvmalloc_node_noprof(), causing a kernel WARNING, TAINT_WARN, and panic on CONFIG_PANIC_ON_WARN=y systems.
Add a size bounds check before we invoke the kvzalloc() to reject oversized num_entries early with -EINVAL.
(cherry picked from commit 1fe7bf5457f6efd7be60b17e23163ba54341d73d)
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability in question resides within the Linux kernel's AMDGPU driver implementation, specifically in the drm/amdgpu subsystem where improper input validation leads to potential system instability. This flaw manifests in the GEM_OP GET_MAPPING_INFO operation where the driver fails to validate user-supplied parameters before memory allocation. The core issue occurs at line 1050 in amdgpu_gem.c where kvcalloc() is called with a direct user-provided value for num_entries without any upper bounds verification.
The technical implementation flaw stems from the driver's lack of parameter validation when processing GPU memory management operations. The variable num_entries is treated as an unsigned 32-bit integer while sizeof(drm_amdgpu_gem_vm_entry) equals 32 bytes, creating a mathematical overflow condition. When userspace provides an excessively large value for num_entries, the multiplication of this value with 32 bytes can exceed the maximum value that can be handled by the kernel's memory allocation subsystem, specifically triggering warnings within __kvmalloc_node_noprof() function. This condition results in a kernel WARNING message being logged along with TAINT_WARN flag being set, indicating potential system instability.
The operational impact of this vulnerability extends beyond simple warning messages to potentially cause system panics on configurations where CONFIG_PANIC_ON_WARN is enabled. This represents a significant security concern as it allows for denial-of-service conditions that could be exploited by malicious users or applications to destabilize systems running the affected kernel versions. The vulnerability specifically affects systems utilizing AMDGPU graphics drivers and can be triggered through improper GEM operations, making it particularly concerning for server and workstation environments where system stability is paramount.
The mitigation strategy involves implementing a size bounds check before invoking the memory allocation function to reject oversized num_entries values early in the processing pipeline with an appropriate -EINVAL error code. This approach aligns with security best practices outlined in CWE-129, which addresses improper validation of array indices and buffer overflows. The fix follows established patterns recommended by the ATT&CK framework for kernel-level defenses, specifically targeting privilege escalation and system stability threats that could be leveraged by adversaries to gain unauthorized access or disrupt system operations. The solution ensures that memory allocations remain within safe boundaries while maintaining proper error handling and user feedback mechanisms.
This vulnerability demonstrates the critical importance of input validation in kernel space operations, particularly when dealing with user-supplied parameters that directly influence memory management behavior. The fix represents a defensive programming approach that prevents potential exploitation pathways while maintaining system functionality and stability. The implementation follows standard security practices for preventing buffer overflows and memory allocation abuses that could be leveraged in advanced persistent threat scenarios or privilege escalation attacks targeting kernel-level components.