The Linux kernel's s390/percpu code used the MVIY_PERCPU() macro which stringified arguments already as C string literals, generating assembler macro invocations with whitespace-separated quoted arguments. GNU assembler versions before binutils 2.39 removed whitespace between quoted macro arguments during input scrubbing, causing the macro to be parsed as a single argument and emit warnings, resulting in the assembler skipping the mviy instruction. This omission caused the interrupted per-CPU sequence not to be marked in lowcore, preventing the exception return path from repairing the per-CPU address register after migration. The fix was to pass C string literals directly and separate assembler macro arguments with explicit commas, producing unambiguous invocations compatible with GNU as and LLVM assemblers. This resolves the issue for systems using binutils versions older than 2.39, which Linux still supports.

The vulnerability caused the assembler to omit critical instructions in the s390 per-CPU code path, leading to the per-CPU address register not being properly repaired after migration. This could affect kernel stability or correctness on affected systems using older binutils versions. There is no indication of active exploitation or direct security compromise from the provided data.

A fix is available in the Linux kernel source that changes the macro invocation syntax to be compatible with older binutils versions. Users should update their Linux kernel to a version including this fix. Since this is a source-level fix, recompilation with the patched kernel source is required. There is no indication of vendor advisories stating no action is required.