Re: [PATCH 2/3] arm64: patching: Fix instruction byte order in aarch64_insn_set()

[Catalin Marinas <catalin.marinas@arm.com>]

On Sat, Oct 10, 2026 at 04:50:54PM +0800, Rui Qi wrote:
> aarch64_insn_set() passes the host-endian u32 instruction straight to
> text_poke_memset(), which memset32()'s it into memory in host byte order.
> AArch64 instructions must be little-endian in memory, so on a big-endian
> kernel the written bytes are reversed and the CPU takes an UNDEFINED
> instruction exception when fetching them.  The sibling aarch64_insn_write()
> already converts with cpu_to_le32(); aarch64_insn_set() does not.
> 
> This is reachable in-tree: bpf_arch_text_invalidate() fills freed JIT
> regions with AARCH64_BREAK_FAULT through aarch64_insn_set(), and arm64
> selects HAVE_EBPF_JIT without a big-endian guard, so the path is taken on
> BE kernels with BPF JIT.  The direct-fill loop in the same file already
> cpu_to_le32()'s the constant, confirming the expected byte order.
> 
> Convert the instruction to little-endian before the memset, mirroring
> aarch64_insn_write().  On LE the conversion is a no-op, so behaviour is
> unchanged.

We are just about to remove big-endian support (in 7.4).

-- 
Catalin