linux-kernel - Re: [PATCH 2/3] arm64: use PAGE_KERNEL_ROX directly in alloc_insn

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Date:   Thu, 18 Jun 2020 11:27:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Jessica Yu <jeyu@...nel.org>,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/3] arm64: use PAGE_KERNEL_ROX directly in
 alloc_insn_page

On Thu, Jun 18, 2020 at 08:43:06AM +0200, Christoph Hellwig wrote:
> Use PAGE_KERNEL_ROX directly instead of allocating RWX and setting the
> page read-only just after the allocation.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/arm64/kernel/probes/kprobes.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index d1c95dcf1d7833..cbe49cd117cfec 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -120,15 +120,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  
>  void *alloc_insn_page(void)
>  {
> -	void *page;
> -
> -	page = vmalloc_exec(PAGE_SIZE);
> -	if (page) {
> -		set_memory_ro((unsigned long)page, 1);
> -		set_vm_flush_reset_perms(page);
> -	}
> -
> -	return page;
> +	return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
> +			GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
> +			NUMA_NO_NODE, __func__);
>  }

I think this has the exact same range issue as the x86 user. But it
might be less fatal if their PLT magic can cover the full range.