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Howlett" , "Matthew Wilcox" , "Vlastimil Babka" , "Paul E . McKenney" , "Jann Horn" , "David Hildenbrand" , , , "Muchun Song" , "Richard Henderson" , "Matt Turner" , "Thomas Bogendoerfer" , "James E . J . Bottomley" , "Helge Deller" , "Chris Zankel" , "Max Filippov" , "Arnd Bergmann" , , , , , "Shuah Khan" , "Christian Brauner" , , "Sidhartha Kumar" , "Jeff Xu" , "Christoph Hellwig" , , "John Hubbard" Subject: Re: [PATCH v3 2/5] mm: add PTE_MARKER_GUARD PTE marker From: "Jarkko Sakkinen" To: "Lorenzo Stoakes" , "Andrew Morton" X-Mailer: aerc 0.18.2 References: <7f81287792eef318a7a711d358c00e2e48216f15.1729699916.git.lorenzo.stoakes@oracle.com> In-Reply-To: <7f81287792eef318a7a711d358c00e2e48216f15.1729699916.git.lorenzo.stoakes@oracle.com> X-Rspamd-Queue-Id: 02154A0028 X-Stat-Signature: dhb7ed3ej4so4nrd3ra7odtnhmzzy6md X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1730147674-388031 X-HE-Meta: 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 VTUoql1S ei+H3tAwwFrd7YLFpJy3oh1S90jQa7ZThlVLNSXXj61lkuYCg8+N4+b+5lJNMsjyi4Pa/aVh8+fcnKHxe8im06S8+XBzLHoBXXogQzeI5ciQOqBuf1FaIjR7XO+8yI0qYagWsc7Obc3yD+s7ym+TApnYcNC0lfUlRNZdoJLe3eXzCM8NYWpKlIjQbsmPN6ZG5ug47Wo7dbMDobn9bSPLomFUJ2m9ojASoi41NLDXsroEv6mSNXxREBvvdHKqTwLzVy+6PWHwFbU/yalUGnxVKNQr8r/PMpgtMoxtNmW0HoP8ImcQ3wnXUjIJ8lhtFQa3cmrwQfyHvop+EEFxDMOEB5w3k4Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed Oct 23, 2024 at 7:24 PM EEST, Lorenzo Stoakes wrote: > 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 page= s > 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 singl= e > 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 mark= er > be encountered there, as we explicitly do not support this operation and > this should not occur. > > Acked-by: Vlastimil Babka > Signed-off-by: Lorenzo Stoakes > --- > 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 =3D pte_marker_get(entry); > /* Always copy error entries. */ > - pte_marker dstm =3D srcm & PTE_MARKER_POISONED; > + pte_marker dstm =3D srcm & (PTE_MARKER_POISONED | PTE_MARKER_GUARD); > =20 > /* 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 accesse= s are > * invalid", instead of referring very specifically to hardware memory e= rrors. > * This marker is meant to represent any of various different causes of = this. > + * > + * Note that, when encountered by the faulting logic, PTEs with this mar= ker will > + * result in VM_FAULT_HWPOISON and thus regardless trigger hardware memo= ry 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) > =20 > 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); > } > =20 > /* > 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, str= uct vm_area_struct *vma, > ret =3D 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 =3D VM_FAULT_SIGSEGV; > + goto out_mutex; > } > } > =20 > 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_deta= ils *details, > return !folio_test_anon(folio); > } > =20 > -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; > =20 > - if (zap_drop_file_uffd_wp(details)) > + if (zap_drop_markers(details)) > return; > =20 > for (;;) { > @@ -1671,7 +1671,15 @@ static unsigned long zap_pte_range(struct mmu_gath= er *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_faul= t *vmf) > if (marker & PTE_MARKER_POISONED) > return VM_FAULT_HWPOISON; > =20 > + /* 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); > =20 > 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 Acked-by: Jarkko Sakkinen BR, Jarkko