Add a new PTE marker that results in any access causing the accessing
process to segfault.
This is preferable to PTE_MARKER_POISONED, which results in the same
handling as hardware poisoned memory, and is thus undesirable for cases
where we simply wish to 'soft' poison a range.
This is in preparation for implementing the ability to specify guard pages
at the page table level, i.e. ranges that, when accessed, should cause
process termination.
Additionally, rename zap_drop_file_uffd_wp() to zap_drop_markers() - the
function checks the ZAP_FLAG_DROP_MARKER flag so naming it for this single
purpose was simply incorrect.
We then reuse the same logic to determine whether a zap should clear a
guard entry - this should only be performed on teardown and never on
MADV_DONTNEED or MADV_FREE.
We additionally add a WARN_ON_ONCE() in hugetlb logic should a guard marker
be encountered there, as we explicitly do not support this operation and
this should not occur.
Acked-by: Vlastimil Babka <vbabkba@xxxxxxx>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
include/linux/mm_inline.h | 2 +-
include/linux/swapops.h | 24 +++++++++++++++++++++++-
mm/hugetlb.c | 4 ++++
mm/memory.c | 18 +++++++++++++++---
mm/mprotect.c | 6 ++++--
5 files changed, 47 insertions(+), 7 deletions(-)
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 355cf46a01a6..1b6a917fffa4 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -544,7 +544,7 @@ static inline pte_marker copy_pte_marker(
{
pte_marker srcm = pte_marker_get(entry);
/* Always copy error entries. */
- pte_marker dstm = srcm & PTE_MARKER_POISONED;
+ pte_marker dstm = srcm & (PTE_MARKER_POISONED | PTE_MARKER_GUARD);
/* Only copy PTE markers if UFFD register matches. */
if ((srcm & PTE_MARKER_UFFD_WP) && userfaultfd_wp(dst_vma))
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index cb468e418ea1..96f26e29fefe 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -426,9 +426,19 @@ typedef unsigned long pte_marker;
* "Poisoned" here is meant in the very general sense of "future accesses are
* invalid", instead of referring very specifically to hardware memory errors.
* This marker is meant to represent any of various different causes of this.
+ *
+ * Note that, when encountered by the faulting logic, PTEs with this marker will
+ * result in VM_FAULT_HWPOISON and thus regardless trigger hardware memory error
+ * logic.
*/
#define PTE_MARKER_POISONED BIT(1)
-#define PTE_MARKER_MASK (BIT(2) - 1)
+/*
+ * Indicates that, on fault, this PTE will case a SIGSEGV signal to be
+ * sent. This means guard markers behave in effect as if the region were mapped
+ * PROT_NONE, rather than if they were a memory hole or equivalent.
+ */
+#define PTE_MARKER_GUARD BIT(2)
+#define PTE_MARKER_MASK (BIT(3) - 1)
static inline swp_entry_t make_pte_marker_entry(pte_marker marker)
{
@@ -464,6 +474,18 @@ static inline int is_poisoned_swp_entry(swp_entry_t entry)
{
return is_pte_marker_entry(entry) &&
(pte_marker_get(entry) & PTE_MARKER_POISONED);
+
+}
+
+static inline swp_entry_t make_guard_swp_entry(void)
+{
+ return make_pte_marker_entry(PTE_MARKER_GUARD);
+}
+
+static inline int is_guard_swp_entry(swp_entry_t entry)
+{
+ return is_pte_marker_entry(entry) &&
+ (pte_marker_get(entry) & PTE_MARKER_GUARD);
}
/*
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 906294ac85dc..2c8c5da0f5d3 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6353,6 +6353,10 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
ret = VM_FAULT_HWPOISON_LARGE |
VM_FAULT_SET_HINDEX(hstate_index(h));
goto out_mutex;
+ } else if (WARN_ON_ONCE(marker & PTE_MARKER_GUARD)) {
+ /* This isn't supported in hugetlb. */
+ ret = VM_FAULT_SIGSEGV;
+ goto out_mutex;
}
}
diff --git a/mm/memory.c b/mm/memory.c
index 0f614523b9f4..551455cd453f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1455,7 +1455,7 @@ static inline bool should_zap_folio(struct zap_details *details,
return !folio_test_anon(folio);
}
-static inline bool zap_drop_file_uffd_wp(struct zap_details *details)
+static inline bool zap_drop_markers(struct zap_details *details)
{
if (!details)
return false;
@@ -1476,7 +1476,7 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
if (vma_is_anonymous(vma))
return;
- if (zap_drop_file_uffd_wp(details))
+ if (zap_drop_markers(details))
return;
for (;;) {
@@ -1671,7 +1671,15 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
* drop the marker if explicitly requested.
*/
if (!vma_is_anonymous(vma) &&
- !zap_drop_file_uffd_wp(details))
+ !zap_drop_markers(details))
+ continue;
+ } else if (is_guard_swp_entry(entry)) {
+ /*
+ * Ordinary zapping should not remove guard PTE
+ * markers. Only do so if we should remove PTE markers
+ * in general.
+ */
+ if (!zap_drop_markers(details))
continue;
} else if (is_hwpoison_entry(entry) ||
is_poisoned_swp_entry(entry)) {
@@ -4003,6 +4011,10 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
if (marker & PTE_MARKER_POISONED)
return VM_FAULT_HWPOISON;
+ /* Hitting a guard page is always a fatal condition. */
+ if (marker & PTE_MARKER_GUARD)
+ return VM_FAULT_SIGSEGV;
+
if (pte_marker_entry_uffd_wp(entry))
return pte_marker_handle_uffd_wp(vmf);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 0c5d6d06107d..1f671b0667bd 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -236,9 +236,11 @@ static long change_pte_range(struct mmu_gather *tlb,
} else if (is_pte_marker_entry(entry)) {
/*
* Ignore error swap entries unconditionally,
- * because any access should sigbus anyway.
+ * because any access should sigbus/sigsegv
+ * anyway.
*/
- if (is_poisoned_swp_entry(entry))
+ if (is_poisoned_swp_entry(entry) ||
+ is_guard_swp_entry(entry))
continue;
/*
* If this is uffd-wp pte marker and we'd like
--
2.47.0
