5.15-stable review patch. If anyone has any objections, please let me know.
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From: Claudio Imbrenda imbrenda@linux.ibm.com
[ Upstream commit c148dc8e2fa403be501612ee409db866eeed35c0 ]
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 Stable-dep-of: 3f29f6537f54 ("s390/uv: Don't call folio_wait_writeback() without a folio reference") Signed-off-by: Sasha Levin sashal@kernel.org --- 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 56bb0a4829770..bdf4d2bed87c5 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); @@ -297,17 +286,18 @@ 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);