riscv: patch: Flush the icache right after patching to avoid illegal insns

We cannot delay the icache flush after patching some functions as we may
have patched a function that will get called before the icache flush.

The only way to completely avoid such scenario is by flushing the icache
as soon as we patch a function. This will probably be costly as we don't
batch the icache maintenance anymore.

Fixes: 6ca445d8 ("riscv: Fix early ftrace nop patching")
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Closes: https://lore.kernel.org/linux-riscv/20240613-lubricant-breath-061192a9489a@wendy/Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20240624082141.153871-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/ftrace.c

@@ -120,9 +120,6 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
 	mutex_unlock(&text_mutex);
 
-	if (!mod)
-		local_flush_icache_range(rec->ip, rec->ip + MCOUNT_INSN_SIZE);
-
 	return out;
 }
 
@@ -156,9 +153,9 @@ static int __ftrace_modify_code(void *data)
 	} else {
 		while (atomic_read(&param->cpu_count) <= num_online_cpus())
 			cpu_relax();
-	}
 
-	local_flush_icache_all();
+		local_flush_icache_all();
+	}
 
 	return 0;
 }

arch/riscv/kernel/patch.c

@@ -89,6 +89,14 @@ static int __patch_insn_set(void *addr, u8 c, size_t len)
 
 	memset(waddr, c, len);
 
+	/*
+	 * We could have just patched a function that is about to be
+	 * called so make sure we don't execute partially patched
+	 * instructions by flushing the icache as soon as possible.
+	 */
+	local_flush_icache_range((unsigned long)waddr,
+				 (unsigned long)waddr + len);
+
 	patch_unmap(FIX_TEXT_POKE0);
 
 	if (across_pages)
@@ -135,6 +143,14 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
 
 	ret = copy_to_kernel_nofault(waddr, insn, len);
 
+	/*
+	 * We could have just patched a function that is about to be
+	 * called so make sure we don't execute partially patched
+	 * instructions by flushing the icache as soon as possible.
+	 */
+	local_flush_icache_range((unsigned long)waddr,
+				 (unsigned long)waddr + len);
+
 	patch_unmap(FIX_TEXT_POKE0);
 
 	if (across_pages)
@@ -189,9 +205,6 @@ int patch_text_set_nosync(void *addr, u8 c, size_t len)
 
 	ret = patch_insn_set(tp, c, len);
 
-	if (!ret)
-		flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
-
 	return ret;
 }
 NOKPROBE_SYMBOL(patch_text_set_nosync);
@@ -224,9 +237,6 @@ int patch_text_nosync(void *addr, const void *insns, size_t len)
 
 	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);
@@ -253,9 +263,9 @@ static int patch_text_cb(void *data)
 	} else {
 		while (atomic_read(&patch->cpu_count) <= num_online_cpus())
 			cpu_relax();
-	}
 
-	local_flush_icache_all();
+		local_flush_icache_all();
+	}
 
 	return ret;
 }