[PATCH v2 1/1] KVM: s390: fix race in gmap_make_secure

Claudio Imbrenda
2023-04-26T13:48:54Z

This patch fixes a potential race in gmap_make_secure and removes the
last user of follow_page without FOLL_GET.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Fixes: 214d9bbcd3a6 ("s390/mm: provide memory management functions for protected KVM guests")
---
arch/s390/kernel/uv.c | 32 +++++++++++---------------------
1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9f18a4af9c13..cb2ee06df286 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -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 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
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);

--
2.40.0