Re: [PATCH] mm/memory-failure: don't allow to unpoison hw corrupted page

[Andrew Morton]

On Sat,  4 Jun 2022 18:32:29 +0800 zhenwei pi <pizhenwei@xxxxxxxxxxxxx> wrote:

> Currently unpoison_memory(unsigned long pfn) is designed for soft
> poison(hwpoison-inject) only. Unpoisoning a hardware corrupted page
> puts page back buddy only, this leads BUG during accessing on the
> corrupted KPTE.
> 
> Do not allow to unpoison hardware corrupted page in unpoison_memory()
> to avoid BUG like this:
> 
>  Unpoison: Software-unpoisoned page 0x61234
>  BUG: unable to handle page fault for address: ffff888061234000

Thanks.

> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2090,6 +2090,7 @@ int unpoison_memory(unsigned long pfn)
>  {
>  	struct page *page;
>  	struct page *p;
> +	pte_t *kpte;
>  	int ret = -EBUSY;
>  	int freeit = 0;
>  	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
> @@ -2101,6 +2102,13 @@ int unpoison_memory(unsigned long pfn)
>  	p = pfn_to_page(pfn);
>  	page = compound_head(p);
>  
> +	kpte = virt_to_kpte((unsigned long)page_to_virt(p));
> +	if (kpte && !pte_present(*kpte)) {
> +		unpoison_pr_info("Unpoison: Page was hardware poisoned %#lx\n",
> +				 pfn, &unpoison_rs);
> +		return -EPERM;
> +	}
> +
>  	mutex_lock(&mf_mutex);
>  
>  	if (!PageHWPoison(p)) {

I guess we don't want to let fault injection crash the kernel, so a
cc:stable seems appropriate here.

Can we think up a suitable Fixes: commit?  I'm suspecting this bug has
been there for a long time?