CVE-2023-52750

/// Technical description

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

arm64: Restrict CPU_BIG_ENDIAN to GNU as or LLVM IAS 15.x or newer

Prior to LLVM 15.0.0, LLVM's integrated assembler would incorrectly

byte-swap NOP when compiling for big-endian, and the resulting series of

bytes happened to match the encoding of FNMADD S21, S30, S0, S0.

This went unnoticed until commit:

34f66c4c4d5518c1 ("arm64: Use a positive cpucap for FP/SIMD")

Prior to that commit, the kernel would always enable the use of FPSIMD

early in boot when __cpu_setup() initialized CPACR_EL1, and so usage of

FNMADD within the kernel was not detected, but could result in the

corruption of user or kernel FPSIMD state.

After that commit, the instructions happen to trap during boot prior to

FPSIMD being detected and enabled, e.g.

| Unhandled 64-bit el1h sync exception on CPU0, ESR 0x000000001fe00000 -- ASIMD

| CPU: 0 PID: 0 Comm: swapper Not tainted 6.6.0-rc3-00013-g34f66c4c4d55 #1

| Hardware name: linux,dummy-virt

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References