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

[Andy Chiu]

Hi Alex,

On Mon, Jun 24, 2024 at 4:21 PM Alexandre Ghiti <alexghiti at rivosinc.com> wrote:
>
> 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.dooley at microchip.com>
> Closes: https://lore.kernel.org/linux-riscv/20240613-lubricant-breath-061192a9489a@wendy/
> Signed-off-by: Alexandre Ghiti <alexghiti at 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();
> +       }

Sorry, maybe I should point it out directly earlier. But I don't think
this diff chunk is required. Threads running in the else clause from
stop_machine must not run into any patchable entry. If it runs into a
patchable entry, running the local fence.i is not going to fix the
problem.

>
>         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
>

Thanks,
Andy