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mm: add PTE_MARKER_GUARD PTE marker

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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/f47f3d5acca2dcf9bbf655b6d33f3dc713e4a4a0.1730123433.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Vlastimil Babka <vbabkba@suse.cz>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Helge Deller <deller@gmx.de>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes 2024-10-28 14:13:28 +00:00 committed by Andrew Morton
parent 5f6170a469
commit 7c53dfbdb0
5 changed files with 47 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/mm_inline.h
View File

@ -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))

24
include/linux/swapops.h
View File

@ -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);
}
/*

4
mm/hugetlb.c
View File

@ -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;
}
}

18
mm/memory.c
View File

@ -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);

6
mm/mprotect.c
View File

@ -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