From: Gerald Schaefer gerald.schaefer@de.ibm.com
commit ab874f22d35a8058d8fdee5f13eb69d8867efeae upstream.
On older HW or under a hypervisor, w/o the instruction-execution- protection (IEP) facility, and also w/o EDAT-1, a translation-specification exception may be recognized when bit 55 of a pte is one (_PAGE_NOEXEC).
The current code tries to prevent setting _PAGE_NOEXEC in such cases, by removing it within set_pte_at(). However, ptep_set_access_flags() will modify a pte directly, w/o using set_pte_at(). There is at least one scenario where this can result in an active pte with _PAGE_NOEXEC set, which would then lead to a panic due to a translation-specification exception (write to swapped out page):
do_swap_page pte = mk_pte (with _PAGE_NOEXEC bit) set_pte_at (will remove _PAGE_NOEXEC bit in page table, but keep it in local variable pte) vmf->orig_pte = pte (pte still contains _PAGE_NOEXEC bit) do_wp_page wp_page_reuse entry = vmf->orig_pte (still with _PAGE_NOEXEC bit) ptep_set_access_flags (writes entry with _PAGE_NOEXEC bit)
Fix this by clearing _PAGE_NOEXEC already in mk_pte_phys(), where the pgprot value is applied, so that no pte with _PAGE_NOEXEC will ever be visible, if it is not supported. The check in set_pte_at() can then also be removed.
Cc: stable@vger.kernel.org # 4.11+ Fixes: 57d7f939e7bd ("s390: add no-execute support") Signed-off-by: Gerald Schaefer gerald.schaefer@de.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/s390/include/asm/pgtable.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/s390/include/asm/pgtable.h +++ b/arch/s390/include/asm/pgtable.h @@ -1173,8 +1173,6 @@ void gmap_pmdp_idte_global(struct mm_str static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t entry) { - if (!MACHINE_HAS_NX) - pte_val(entry) &= ~_PAGE_NOEXEC; if (pte_present(entry)) pte_val(entry) &= ~_PAGE_UNUSED; if (mm_has_pgste(mm)) @@ -1191,6 +1189,8 @@ static inline pte_t mk_pte_phys(unsigned { pte_t __pte; pte_val(__pte) = physpage + pgprot_val(pgprot); + if (!MACHINE_HAS_NX) + pte_val(__pte) &= ~_PAGE_NOEXEC; return pte_mkyoung(__pte); }