arm64: patching: Add aarch64_insn_write_literal_u64()

In subsequent patches we'll need to atomically write to a
naturally-aligned 64-bit literal embedded within the kernel text.

Add a helper for this. For consistency with other text patching code we
use copy_to_kernel_nofault(), which is atomic for naturally-aligned
accesses up to 64-bits.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230123134603.1064407-7-mark.rutland@arm.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/patching.h

@@ -7,6 +7,8 @@
 int aarch64_insn_read(void *addr, u32 *insnp);
 int aarch64_insn_write(void *addr, u32 insn);
 
+int aarch64_insn_write_literal_u64(void *addr, u64 val);
+
 int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
 int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
 

arch/arm64/kernel/patching.c

@@ -88,6 +88,23 @@ int __kprobes aarch64_insn_write(void *addr, u32 insn)
 	return __aarch64_insn_write(addr, cpu_to_le32(insn));
 }
 
+noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
+{
+	u64 *waddr;
+	unsigned long flags;
+	int ret;
+
+	raw_spin_lock_irqsave(&patch_lock, flags);
+	waddr = patch_map(addr, FIX_TEXT_POKE0);
+
+	ret = copy_to_kernel_nofault(waddr, &val, sizeof(val));
+
+	patch_unmap(FIX_TEXT_POKE0);
+	raw_spin_unlock_irqrestore(&patch_lock, flags);
+
+	return ret;
+}
+
 int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
 {
 	u32 *tp = addr;