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authorClaudio Imbrenda <imbrenda@linux.ibm.com>2023-04-28 11:27:53 +0200
committerClaudio Imbrenda <imbrenda@linux.ibm.com>2023-05-04 18:26:27 +0200
commitc148dc8e2fa403be501612ee409db866eeed35c0 (patch)
tree7f2c58e528c596849603797177ba515c69bbacf3 /arch
parent292a7d6fca33df70ca4b8e9b0d0e74adf87582dc (diff)
downloadlwn-c148dc8e2fa403be501612ee409db866eeed35c0.tar.gz
lwn-c148dc8e2fa403be501612ee409db866eeed35c0.zip
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: 214d9bbcd3a6 ("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>
Diffstat (limited to 'arch')
-rw-r--r--arch/s390/kernel/uv.c32
1 files 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 @@ 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);