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KVM: s390: fix race in gmap_make_secure() 

Fix a potential race in gmap_make_secure() and remove the last user of
follow_page() without FOLL_GET.

The old code is locking something it doesn't have a reference to, and
as explained by Jason and David in this discussion:
https://lore.kernel.org/linux-mm/Y9J4P%2FRNvY1Ztn0Q@nvidia.com/
it can lead to all kind of bad things, including the page getting
unmapped (MADV_DONTNEED), freed, reallocated as a larger folio and the
unlock_page() would target the wrong bit.
There is also another race with the FOLL_WRITE, which could race
between the follow_page() and the get_locked_pte().

The main point is to remove the last use of follow_page() without
FOLL_GET or FOLL_PIN, removing the races can be considered a nice
bonus.

Link: https://lore.kernel.org/linux-mm/Y9J4P%2FRNvY1Ztn0Q@nvidia.com/
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Fixes: 214d9bbcd3 ("s390/mm: provide memory management functions for protected KVM guests")
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20230428092753.27913-2-imbrenda@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda 2023-04-28 11:27:53 +02:00
parent 292a7d6fca
commit c148dc8e2f
1 changed files with 11 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
arch/s390/kernel/uv.c
View File

@ -192,21 +192,10 @@ static int expected_page_refs(struct page *page)
return res;
}
static int make_secure_pte(pte_t *ptep, unsigned long addr,
struct page *exp_page, struct uv_cb_header *uvcb)
static int make_page_secure(struct page *page, struct uv_cb_header *uvcb)
{
pte_t entry = READ_ONCE(*ptep);
struct page *page;
int expected, cc = 0;
if (!pte_present(entry))
return -ENXIO;
if (pte_val(entry) & _PAGE_INVALID)
return -ENXIO;
page = pte_page(entry);
if (page != exp_page)
return -ENXIO;
if (PageWriteback(page))
return -EAGAIN;
expected = expected_page_refs(page);
@ -304,17 +293,18 @@ again:
goto out;
rc = -ENXIO;
page = follow_page(vma, uaddr, FOLL_WRITE);
if (IS_ERR_OR_NULL(page))
goto out;
lock_page(page);
ptep = get_locked_pte(gmap->mm, uaddr, &ptelock);
if (should_export_before_import(uvcb, gmap->mm))
uv_convert_from_secure(page_to_phys(page));
rc = make_secure_pte(ptep, uaddr, page, uvcb);
if (pte_present(*ptep) && !(pte_val(*ptep) & _PAGE_INVALID) && pte_write(*ptep)) {
page = pte_page(*ptep);
rc = -EAGAIN;
if (trylock_page(page)) {
if (should_export_before_import(uvcb, gmap->mm))
uv_convert_from_secure(page_to_phys(page));
rc = make_page_secure(page, uvcb);
unlock_page(page);
}
}
pte_unmap_unlock(ptep, ptelock);
unlock_page(page);
out:
mmap_read_unlock(gmap->mm);