1 files changed, 164 insertions, 0 deletions
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
new file mode 100644
index 000000000..160e5c1ca
--- /dev/null
+++ b/arch/riscv/kernel/patch.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 SiFive
+ */
+
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/memory.h>
+#include <linux/uaccess.h>
+#include <linux/stop_machine.h>
+#include <asm/kprobes.h>
+#include <asm/cacheflush.h>
+#include <asm/fixmap.h>
+#include <asm/ftrace.h>
+#include <asm/patch.h>
+#include <asm/sections.h>
+
+struct patch_insn {
+	void *addr;
+	u32 insn;
+	atomic_t cpu_count;
+};
+
+int riscv_patch_in_stop_machine = false;
+
+#ifdef CONFIG_MMU
+
+static inline bool is_kernel_exittext(uintptr_t addr)
+{
+	return system_state < SYSTEM_RUNNING &&
+		addr >= (uintptr_t)__exittext_begin &&
+		addr < (uintptr_t)__exittext_end;
+}
+
+/*
+ * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
+ * reg-a0) or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
+ * So use '__always_inline' and 'const unsigned int fixmap' here.
+ */
+static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
+{
+	uintptr_t uintaddr = (uintptr_t) addr;
+	struct page *page;
+
+	if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr))
+		page = phys_to_page(__pa_symbol(addr));
+	else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+		page = vmalloc_to_page(addr);
+	else
+		return addr;
+
+	BUG_ON(!page);
+
+	return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
+					 (uintaddr & ~PAGE_MASK));
+}
+
+static void patch_unmap(int fixmap)
+{
+	clear_fixmap(fixmap);
+}
+NOKPROBE_SYMBOL(patch_unmap);
+
+static int patch_insn_write(void *addr, const void *insn, size_t len)
+{
+	void *waddr = addr;
+	bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
+	int ret;
+
+	/*
+	 * Before reaching here, it was expected to lock the text_mutex
+	 * already, so we don't need to give another lock here and could
+	 * ensure that it was safe between each cores.
+	 *
+	 * We're currently using stop_machine() for ftrace & kprobes, and while
+	 * that ensures text_mutex is held before installing the mappings it
+	 * does not ensure text_mutex is held by the calling thread.  That's
+	 * safe but triggers a lockdep failure, so just elide it for that
+	 * specific case.
+	 */
+	if (!riscv_patch_in_stop_machine)
+		lockdep_assert_held(&text_mutex);
+
+	if (across_pages)
+		patch_map(addr + len, FIX_TEXT_POKE1);
+
+	waddr = patch_map(addr, FIX_TEXT_POKE0);
+
+	ret = copy_to_kernel_nofault(waddr, insn, len);
+
+	patch_unmap(FIX_TEXT_POKE0);
+
+	if (across_pages)
+		patch_unmap(FIX_TEXT_POKE1);
+
+	return ret;
+}
+NOKPROBE_SYMBOL(patch_insn_write);
+#else
+static int patch_insn_write(void *addr, const void *insn, size_t len)
+{
+	return copy_to_kernel_nofault(addr, insn, len);
+}
+NOKPROBE_SYMBOL(patch_insn_write);
+#endif /* CONFIG_MMU */
+
+int patch_text_nosync(void *addr, const void *insns, size_t len)
+{
+	u32 *tp = addr;
+	int ret;
+
+	ret = patch_insn_write(tp, insns, len);
+
+	if (!ret)
+		flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
+
+	return ret;
+}
+NOKPROBE_SYMBOL(patch_text_nosync);
+
+static int patch_text_cb(void *data)
+{
+	struct patch_insn *patch = data;
+	int ret = 0;
+
+	if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
+		ret =
+		    patch_text_nosync(patch->addr, &patch->insn,
+					    GET_INSN_LENGTH(patch->insn));
+		atomic_inc(&patch->cpu_count);
+	} else {
+		while (atomic_read(&patch->cpu_count) <= num_online_cpus())
+			cpu_relax();
+		smp_mb();
+	}
+
+	return ret;
+}
+NOKPROBE_SYMBOL(patch_text_cb);
+
+int patch_text(void *addr, u32 insn)
+{
+	int ret;
+	struct patch_insn patch = {
+		.addr = addr,
+		.insn = insn,
+		.cpu_count = ATOMIC_INIT(0),
+	};
+
+	/*
+	 * kprobes takes text_mutex, before calling patch_text(), but as we call
+	 * calls stop_machine(), the lockdep assertion in patch_insn_write()
+	 * gets confused by the context in which the lock is taken.
+	 * Instead, ensure the lock is held before calling stop_machine(), and
+	 * set riscv_patch_in_stop_machine to skip the check in
+	 * patch_insn_write().
+	 */
+	lockdep_assert_held(&text_mutex);
+	riscv_patch_in_stop_machine = true;
+	ret = stop_machine_cpuslocked(patch_text_cb, &patch, cpu_online_mask);
+	riscv_patch_in_stop_machine = false;
+	return ret;
+}
+NOKPROBE_SYMBOL(patch_text);