linux-kernel - Re: [PATCH 2/3] mm/pagemap: Fix wr-protect even if PM_SCAN_WP

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Date:   Fri, 17 Nov 2023 07:27:40 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        syzbot+7ca4b2719dc742b8d0a4@...kaller.appspotmail.com
Subject: Re: [PATCH 2/3] mm/pagemap: Fix wr-protect even if
 PM_SCAN_WP_MATCHING not set

On Thu, Nov 16, 2023 at 12:15 PM Peter Xu <peterx@...hat.com> wrote:
>
> The new pagemap ioctl contains a fast path for wr-protections without
> looking into category masks.  It forgets to check PM_SCAN_WP_MATCHING
> before applying the wr-protections.  It can cause, e.g., pte markers
> installed on archs that do not even support uffd wr-protect.
>
> WARNING: CPU: 0 PID: 5059 at mm/memory.c:1520 zap_pte_range mm/memory.c:1520 [inline]
>
> Fixes: 12f6b01a0bcb ("fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag")
> Reported-by: syzbot+7ca4b2719dc742b8d0a4@...kaller.appspotmail.com
> Signed-off-by: Peter Xu <peterx@...hat.com>

Reviewed-by: Andrei Vagin <avagin@...il.com>

> ---
>  fs/proc/task_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e91085d79926..d19924bf0a39 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -2171,7 +2171,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
>                 return 0;
>         }
>
> -       if (!p->vec_out) {
> +       if ((p->arg.flags & PM_SCAN_WP_MATCHING) && !p->vec_out) {
>                 /* Fast path for performing exclusive WP */
>                 for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
>                         if (pte_uffd_wp(ptep_get(pte)))
> --
> 2.41.0
>