The patch titled
Subject: mm: add PTE_MARKER_GUARD PTE marker
has been added to the -mm mm-unstable branch. Its filename is
mm-add-pte_marker_guard-pte-marker.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-pte_marker_guard-pte-marker.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Subject: mm: add PTE_MARKER_GUARD PTE marker
Date: Wed, 23 Oct 2024 17:24:39 +0100
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.
Link: https://lkml.kernel.org/r/7f81287792eef318a7a711d358c00e2e48216f15.1729699916.git.lorenzo.stoakes@xxxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabkba@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Chris Zankel <chris@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: James E.J. Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jeff Xu <jeffxu@xxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Matt Turner <mattst88@xxxxxxxxx>
Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Richard Henderson <richard.henderson@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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(-)
--- a/include/linux/mm_inline.h~mm-add-pte_marker_guard-pte-marker
+++ a/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))
--- a/include/linux/swapops.h~mm-add-pte_marker_guard-pte-marker
+++ a/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(
{
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);
}
/*
--- a/mm/hugetlb.c~mm-add-pte_marker_guard-pte-marker
+++ a/mm/hugetlb.c
@@ -6353,6 +6353,10 @@ vm_fault_t hugetlb_fault(struct mm_struc
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;
}
}
--- a/mm/memory.c~mm-add-pte_marker_guard-pte-marker
+++ a/mm/memory.c
@@ -1455,7 +1455,7 @@ static inline bool should_zap_folio(stru
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_
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(struc
* 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(stru
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);
--- a/mm/mprotect.c~mm-add-pte_marker_guard-pte-marker
+++ a/mm/mprotect.c
@@ -236,9 +236,11 @@ static long change_pte_range(struct mmu_
} 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
_
Patches currently in -mm which might be from lorenzo.stoakes@xxxxxxxxxx are
fork-do-not-invoke-uffd-on-fork-if-error-occurs.patch
fork-only-invoke-khugepaged-ksm-hooks-if-no-error.patch
mm-vma-add-expand-only-vma-merge-mode-and-optimise-do_brk_flags.patch
tools-testing-add-expand-only-mode-vma-test.patch
mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook.patch
mm-unconditionally-close-vmas-on-error.patch
mm-refactor-map_deny_write_exec.patch
mm-resolve-faulty-mmap_region-error-path-behaviour.patch
selftests-mm-add-pkey_sighandler_xx-hugetlb_dio-to-gitignore.patch
mm-refactor-mm_access-to-not-return-null.patch
mm-refactor-mm_access-to-not-return-null-fix.patch
mm-madvise-unrestrict-process_madvise-for-current-process.patch
maple_tree-do-not-hash-pointers-on-dump-in-debug-mode.patch
tools-testing-fix-phys_addr_t-size-on-64-bit-systems.patch
tools-testing-add-additional-vma_internalh-stubs.patch
mm-isolate-mmap-internal-logic-to-mm-vmac.patch
mm-refactor-__mmap_region.patch
mm-defer-second-attempt-at-merge-on-mmap.patch
mm-pagewalk-add-the-ability-to-install-ptes.patch
mm-add-pte_marker_guard-pte-marker.patch
mm-madvise-implement-lightweight-guard-page-mechanism.patch
tools-testing-update-tools-uapi-header-for-mman-commonh.patch
selftests-mm-add-self-tests-for-guard-page-feature.patch
