lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20211115165446.022539392@linuxfoundation.org>
Date:   Mon, 15 Nov 2021 18:00:04 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 509/917] s390/mm: fix VMA and page table handling code in storage key handling functions

From: David Hildenbrand <david@...hat.com>

[ Upstream commit 949f5c1244ee6c36d2e81c588d1200eaa83a3df6 ]

There are multiple things broken about our storage key handling
functions:

1. We should not walk/touch page tables outside of VMA boundaries when
   holding only the mmap sem in read mode. Evil user space can modify the
   VMA layout just before this function runs and e.g., trigger races with
   page table removal code since commit dd2283f2605e ("mm: mmap: zap pages
   with read mmap_sem in munmap"). gfn_to_hva() will only translate using
   KVM memory regions, but won't validate the VMA.

2. We should not allocate page tables outside of VMA boundaries: if
   evil user space decides to map hugetlbfs to these ranges, bad things
   will happen because we suddenly have PTE or PMD page tables where we
   shouldn't have them.

3. We don't handle large PUDs that might suddenly appeared inside our page
   table hierarchy.

Don't manually allocate page tables, properly validate that we have VMA and
bail out on pud_large().

All callers of page table handling functions, except
get_guest_storage_key(), call fixup_user_fault() in case they
receive an -EFAULT and retry; this will allocate the necessary page tables
if required.

To keep get_guest_storage_key() working as expected and not requiring
kvm_s390_get_skeys() to call fixup_user_fault() distinguish between
"there is simply no page table or huge page yet and the key is assumed
to be 0" and "this is a fault to be reported".

Although commit 637ff9efe5ea ("s390/mm: Add huge pmd storage key handling")
introduced most of the affected code, it was actually already broken
before when using get_locked_pte() without any VMA checks.

Note: Ever since commit 637ff9efe5ea ("s390/mm: Add huge pmd storage key
handling") we can no longer set a guest storage key (for example from
QEMU during VM live migration) without actually resolving a fault.
Although we would have created most page tables, we would choke on the
!pmd_present(), requiring a call to fixup_user_fault(). I would
have thought that this is problematic in combination with postcopy life
migration ... but nobody noticed and this patch doesn't change the
situation. So maybe it's just fine.

Fixes: 9fcf93b5de06 ("KVM: S390: Create helper function get_guest_storage_key")
Fixes: 24d5dd0208ed ("s390/kvm: Provide function for setting the guest storage key")
Fixes: a7e19ab55ffd ("KVM: s390: handle missing storage-key facility")
Signed-off-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Acked-by: Heiko Carstens <hca@...ux.ibm.com>
Link: https://lore.kernel.org/r/20210909162248.14969-5-david@redhat.com
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/s390/mm/pgtable.c | 57 +++++++++++++++++++++++++++++-------------
 1 file changed, 39 insertions(+), 18 deletions(-)

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 2717a406edeb3..6ad634a27d5b9 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -429,22 +429,36 @@ static inline pmd_t pmdp_flush_lazy(struct mm_struct *mm,
 }
 
 #ifdef CONFIG_PGSTE
-static pmd_t *pmd_alloc_map(struct mm_struct *mm, unsigned long addr)
+static int pmd_lookup(struct mm_struct *mm, unsigned long addr, pmd_t **pmdp)
 {
+	struct vm_area_struct *vma;
 	pgd_t *pgd;
 	p4d_t *p4d;
 	pud_t *pud;
-	pmd_t *pmd;
+
+	/* We need a valid VMA, otherwise this is clearly a fault. */
+	vma = vma_lookup(mm, addr);
+	if (!vma)
+		return -EFAULT;
 
 	pgd = pgd_offset(mm, addr);
-	p4d = p4d_alloc(mm, pgd, addr);
-	if (!p4d)
-		return NULL;
-	pud = pud_alloc(mm, p4d, addr);
-	if (!pud)
-		return NULL;
-	pmd = pmd_alloc(mm, pud, addr);
-	return pmd;
+	if (!pgd_present(*pgd))
+		return -ENOENT;
+
+	p4d = p4d_offset(pgd, addr);
+	if (!p4d_present(*p4d))
+		return -ENOENT;
+
+	pud = pud_offset(p4d, addr);
+	if (!pud_present(*pud))
+		return -ENOENT;
+
+	/* Large PUDs are not supported yet. */
+	if (pud_large(*pud))
+		return -EFAULT;
+
+	*pmdp = pmd_offset(pud, addr);
+	return 0;
 }
 #endif
 
@@ -778,8 +792,7 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
 	pmd_t *pmdp;
 	pte_t *ptep;
 
-	pmdp = pmd_alloc_map(mm, addr);
-	if (unlikely(!pmdp))
+	if (pmd_lookup(mm, addr, &pmdp))
 		return -EFAULT;
 
 	ptl = pmd_lock(mm, pmdp);
@@ -881,8 +894,7 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr)
 	pte_t *ptep;
 	int cc = 0;
 
-	pmdp = pmd_alloc_map(mm, addr);
-	if (unlikely(!pmdp))
+	if (pmd_lookup(mm, addr, &pmdp))
 		return -EFAULT;
 
 	ptl = pmd_lock(mm, pmdp);
@@ -935,15 +947,24 @@ int get_guest_storage_key(struct mm_struct *mm, unsigned long addr,
 	pmd_t *pmdp;
 	pte_t *ptep;
 
-	pmdp = pmd_alloc_map(mm, addr);
-	if (unlikely(!pmdp))
+	/*
+	 * If we don't have a PTE table and if there is no huge page mapped,
+	 * the storage key is 0.
+	 */
+	*key = 0;
+
+	switch (pmd_lookup(mm, addr, &pmdp)) {
+	case -ENOENT:
+		return 0;
+	case 0:
+		break;
+	default:
 		return -EFAULT;
+	}
 
 	ptl = pmd_lock(mm, pmdp);
 	if (!pmd_present(*pmdp)) {
-		/* Not yet mapped memory has a zero key */
 		spin_unlock(ptl);
-		*key = 0;
 		return 0;
 	}
 
-- 
2.33.0



Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ