[PATCH -fixes] riscv: patch: Flush the icache right after patching to avoid illegal insns

[Alexandre Ghiti]

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: 6ca445d8af0e ("riscv: Fix early ftrace nop patching")
Reported-by: Conor Dooley <conor.doo...@microchip.com>
Closes: 
https://lore.kernel.org/linux-riscv/20240613-lubricant-breath-061192a9489a@wendy/
Signed-off-by: Alexandre Ghiti <alexgh...@rivosinc.com>
---
 arch/riscv/kernel/ftrace.c |  7 ++-----
 arch/riscv/kernel/patch.c  | 26 ++++++++++++++++++--------
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 87cbd86576b2..4b95c574fd04 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/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;
 }
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 4007563fb607..ab03732d06c4 100644
--- a/arch/riscv/kernel/patch.c
+++ b/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;
 }
-- 
2.39.2