x86/speculation/l1tf: Disallow non privileged high MMIO PROT_NONE mappings
commit 42e4089c7890725fcd329999252dc489b72f2921 upstream.
For L1TF PROT_NONE mappings are protected by inverting the PFN in the page
table entry. This sets the high bits in the CPU's address space, thus
making sure to point to not point an unmapped entry to valid cached memory.
Some server system BIOSes put the MMIO mappings high up in the physical
address space. If such an high mapping was mapped to unprivileged users
they could attack low memory by setting such a mapping to PROT_NONE. This
could happen through a special device driver which is not access
protected. Normal /dev/mem is of course access protected.
To avoid this forbid PROT_NONE mappings or mprotect for high MMIO mappings.
Valid page mappings are allowed because the system is then unsafe anyways.
It's not expected that users commonly use PROT_NONE on MMIO. But to
minimize any impact this is only enforced if the mapping actually refers to
a high MMIO address (defined as the MAX_PA-1 bit being set), and also skip
the check for root.
For mmaps this is straight forward and can be handled in vm_insert_pfn and
in remap_pfn_range().
For mprotect it's a bit trickier. At the point where the actual PTEs are
accessed a lot of state has been changed and it would be difficult to undo
on an error. Since this is a uncommon case use a separate early page talk
walk pass for MMIO PROT_NONE mappings that checks for this condition
early. For non MMIO and non PROT_NONE there are no changes.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index efbe653..ed4d50a 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1338,6 +1338,14 @@
return __pte_access_permitted(pud_val(pud), write);
}
+#define __HAVE_ARCH_PFN_MODIFY_ALLOWED 1
+extern bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot);
+
+static inline bool arch_has_pfn_modify_check(void)
+{
+ return boot_cpu_has_bug(X86_BUG_L1TF);
+}
+
#include <asm-generic/pgtable.h>
#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 48c5912..f40ab81 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -240,3 +240,24 @@
return phys_addr_valid(addr + count - 1);
}
+
+/*
+ * Only allow root to set high MMIO mappings to PROT_NONE.
+ * This prevents an unpriv. user to set them to PROT_NONE and invert
+ * them, then pointing to valid memory for L1TF speculation.
+ *
+ * Note: for locked down kernels may want to disable the root override.
+ */
+bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
+{
+ if (!boot_cpu_has_bug(X86_BUG_L1TF))
+ return true;
+ if (!__pte_needs_invert(pgprot_val(prot)))
+ return true;
+ /* If it's real memory always allow */
+ if (pfn_valid(pfn))
+ return true;
+ if (pfn > l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
+ return false;
+ return true;
+}
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index f59639a..0ecc119 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1097,4 +1097,16 @@
#endif
#endif
+#ifndef __HAVE_ARCH_PFN_MODIFY_ALLOWED
+static inline bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
+{
+ return true;
+}
+
+static inline bool arch_has_pfn_modify_check(void)
+{
+ return false;
+}
+#endif
+
#endif /* _ASM_GENERIC_PGTABLE_H */
diff --git a/mm/memory.c b/mm/memory.c
index c5e87a3..0e356dd 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1884,6 +1884,9 @@
if (addr < vma->vm_start || addr >= vma->vm_end)
return -EFAULT;
+ if (!pfn_modify_allowed(pfn, pgprot))
+ return -EACCES;
+
track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV));
ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
@@ -1919,6 +1922,9 @@
track_pfn_insert(vma, &pgprot, pfn);
+ if (!pfn_modify_allowed(pfn_t_to_pfn(pfn), pgprot))
+ return -EACCES;
+
/*
* If we don't have pte special, then we have to use the pfn_valid()
* based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
@@ -1980,6 +1986,7 @@
{
pte_t *pte;
spinlock_t *ptl;
+ int err = 0;
pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
if (!pte)
@@ -1987,12 +1994,16 @@
arch_enter_lazy_mmu_mode();
do {
BUG_ON(!pte_none(*pte));
+ if (!pfn_modify_allowed(pfn, prot)) {
+ err = -EACCES;
+ break;
+ }
set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
pfn++;
} while (pte++, addr += PAGE_SIZE, addr != end);
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(pte - 1, ptl);
- return 0;
+ return err;
}
static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
@@ -2001,6 +2012,7 @@
{
pmd_t *pmd;
unsigned long next;
+ int err;
pfn -= addr >> PAGE_SHIFT;
pmd = pmd_alloc(mm, pud, addr);
@@ -2009,9 +2021,10 @@
VM_BUG_ON(pmd_trans_huge(*pmd));
do {
next = pmd_addr_end(addr, end);
- if (remap_pte_range(mm, pmd, addr, next,
- pfn + (addr >> PAGE_SHIFT), prot))
- return -ENOMEM;
+ err = remap_pte_range(mm, pmd, addr, next,
+ pfn + (addr >> PAGE_SHIFT), prot);
+ if (err)
+ return err;
} while (pmd++, addr = next, addr != end);
return 0;
}
@@ -2022,6 +2035,7 @@
{
pud_t *pud;
unsigned long next;
+ int err;
pfn -= addr >> PAGE_SHIFT;
pud = pud_alloc(mm, p4d, addr);
@@ -2029,9 +2043,10 @@
return -ENOMEM;
do {
next = pud_addr_end(addr, end);
- if (remap_pmd_range(mm, pud, addr, next,
- pfn + (addr >> PAGE_SHIFT), prot))
- return -ENOMEM;
+ err = remap_pmd_range(mm, pud, addr, next,
+ pfn + (addr >> PAGE_SHIFT), prot);
+ if (err)
+ return err;
} while (pud++, addr = next, addr != end);
return 0;
}
@@ -2042,6 +2057,7 @@
{
p4d_t *p4d;
unsigned long next;
+ int err;
pfn -= addr >> PAGE_SHIFT;
p4d = p4d_alloc(mm, pgd, addr);
@@ -2049,9 +2065,10 @@
return -ENOMEM;
do {
next = p4d_addr_end(addr, end);
- if (remap_pud_range(mm, p4d, addr, next,
- pfn + (addr >> PAGE_SHIFT), prot))
- return -ENOMEM;
+ err = remap_pud_range(mm, p4d, addr, next,
+ pfn + (addr >> PAGE_SHIFT), prot);
+ if (err)
+ return err;
} while (p4d++, addr = next, addr != end);
return 0;
}
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 625608b..6d33162 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -306,6 +306,42 @@
return pages;
}
+static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
+ 0 : -EACCES;
+}
+
+static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
+ unsigned long addr, unsigned long next,
+ struct mm_walk *walk)
+{
+ return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
+ 0 : -EACCES;
+}
+
+static int prot_none_test(unsigned long addr, unsigned long next,
+ struct mm_walk *walk)
+{
+ return 0;
+}
+
+static int prot_none_walk(struct vm_area_struct *vma, unsigned long start,
+ unsigned long end, unsigned long newflags)
+{
+ pgprot_t new_pgprot = vm_get_page_prot(newflags);
+ struct mm_walk prot_none_walk = {
+ .pte_entry = prot_none_pte_entry,
+ .hugetlb_entry = prot_none_hugetlb_entry,
+ .test_walk = prot_none_test,
+ .mm = current->mm,
+ .private = &new_pgprot,
+ };
+
+ return walk_page_range(start, end, &prot_none_walk);
+}
+
int
mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
unsigned long start, unsigned long end, unsigned long newflags)
@@ -324,6 +360,19 @@
}
/*
+ * Do PROT_NONE PFN permission checks here when we can still
+ * bail out without undoing a lot of state. This is a rather
+ * uncommon case, so doesn't need to be very optimized.
+ */
+ if (arch_has_pfn_modify_check() &&
+ (vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
+ (newflags & (VM_READ|VM_WRITE|VM_EXEC)) == 0) {
+ error = prot_none_walk(vma, start, end, newflags);
+ if (error)
+ return error;
+ }
+
+ /*
* If we make a private mapping writable we increase our commit;
* but (without finer accounting) cannot reduce our commit if we
* make it unwritable again. hugetlb mapping were accounted for
