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

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Date: Tue, 25 Jun 2024 10:38:59 +0800
From: Andy Chiu <andy.chiu@...ive.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Björn Töpel <bjorn@...osinc.com>, 
	Puranjay Mohan <puranjay12@...il.com>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH -fixes] riscv: patch: Flush the icache right after
 patching to avoid illegal insns

On Mon, Jun 24, 2024 at 7:49 PM Andy Chiu <andy.chiu@...ive.com> wrote:
>
> Hi Alex,
>
> On Mon, Jun 24, 2024 at 4:21 PM Alexandre Ghiti <alexghiti@...osinc.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@...rochip.com>
> > Closes: https://lore.kernel.org/linux-riscv/20240613-lubricant-breath-061192a9489a@wendy/
> > Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>

Reviewed-by: Andy Chiu <andy.chiu@...ive.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.

Sorry, I read the code wrong. The local flush is not in the while
loop. I have no problem with this chunk after properly seeing them.

>
> >
> >         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