linux-kernel - Re: [PATCH] RISC-V: Don't mark init section as non-executable

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Date:   Mon, 1 Jun 2020 09:50:13 +0530
From:   Anup Patel <anup@...infault.org>
To:     Anup Patel <anup.patel@....com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] RISC-V: Don't mark init section as non-executable

On Sun, May 31, 2020 at 3:28 PM Anup Patel <anup.patel@....com> wrote:
>
> The head text section (i.e. _start, secondary_start_sbi, etc) and the
> init section fall under same page table level-1 mapping.
>
> Currently, the runtime CPU hotplug is broken because we are marking
> init section as non-executable which in-turn marks head text section
> as non-executable.
>
> Further investigating other architectures, it seems marking the init
> section as non-executable is redundant because the init section pages
> are anyway poisoned and freed.
>
> To fix broken runtime CPU hotplug, we simply remove the code marking
> the init section as non-executable.
>
> Fixes: d27c3c90817e ("riscv: add STRICT_KERNEL_RWX support")
> Cc: stable@...r.kernel.org
> Signed-off-by: Anup Patel <anup.patel@....com>
> ---
>  arch/riscv/mm/init.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 736de6c8739f..e0f8ccab8a41 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -482,11 +482,6 @@ static void __init setup_vm_final(void)
>
>  void free_initmem(void)
>  {
> -       unsigned long init_begin = (unsigned long)__init_begin;
> -       unsigned long init_end = (unsigned long)__init_end;
> -
> -       /* Make the region as non-execuatble. */
> -       set_memory_nx(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
>         free_initmem_default(POISON_FREE_INITMEM);
>  }

I just realized that updated free_initmem() over here is exactly
same as generic free_initmem() defined in init/main.c so it's better
to remove free_initmem() from here. I will send v2.

Regards,
Anup