[PATCH v2 1/2] mm/memfd: reserve hugetlb folios before allocation
David Hildenbrand
david at redhat.com
Fri Jan 17 16:54:29 UTC 2025
On 14.01.25 09:08, Vivek Kasireddy wrote:
> There are cases when we try to pin a folio but discover that it has
> not been faulted-in. So, we try to allocate it in memfd_alloc_folio()
> but there is a chance that we might encounter a crash/failure
> (VM_BUG_ON(!h->resv_huge_pages)) if there are no active reservations
> at that instant. This issue was reported by syzbot:
>
> kernel BUG at mm/hugetlb.c:2403!
> Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
> CPU: 0 UID: 0 PID: 5315 Comm: syz.0.0 Not tainted
> 6.13.0-rc5-syzkaller-00161-g63676eefb7a0 #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:alloc_hugetlb_folio_reserve+0xbc/0xc0 mm/hugetlb.c:2403
> Code: 1f eb 05 e8 56 18 a0 ff 48 c7 c7 40 56 61 8e e8 ba 21 cc 09 4c 89
> f0 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc e8 35 18 a0 ff 90 <0f> 0b 66
> 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f
> RSP: 0018:ffffc9000d3d77f8 EFLAGS: 00010087
> RAX: ffffffff81ff6beb RBX: 0000000000000000 RCX: 0000000000100000
> RDX: ffffc9000e51a000 RSI: 00000000000003ec RDI: 00000000000003ed
> RBP: 1ffffffff34810d9 R08: ffffffff81ff6ba3 R09: 1ffffd4000093005
> R10: dffffc0000000000 R11: fffff94000093006 R12: dffffc0000000000
> R13: dffffc0000000000 R14: ffffea0000498000 R15: ffffffff9a4086c8
> FS: 00007f77ac12e6c0(0000) GS:ffff88801fc00000(0000)
> knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f77ab54b170 CR3: 0000000040b70000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> memfd_alloc_folio+0x1bd/0x370 mm/memfd.c:88
> memfd_pin_folios+0xf10/0x1570 mm/gup.c:3750
> udmabuf_pin_folios drivers/dma-buf/udmabuf.c:346 [inline]
> udmabuf_create+0x70e/0x10c0 drivers/dma-buf/udmabuf.c:443
> udmabuf_ioctl_create drivers/dma-buf/udmabuf.c:495 [inline]
> udmabuf_ioctl+0x301/0x4e0 drivers/dma-buf/udmabuf.c:526
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:906 [inline]
> __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Therefore, to avoid this situation and fix this issue, we just need
> to make a reservation (by calling hugetlb_reserve_pages()) before
> we try to allocate the folio. This will ensure that we are properly
> doing region/subpool accounting associated with our allocation.
>
> While at it, move subpool_inode() into hugetlb header and also
> replace the VM_BUG_ON() with WARN_ON_ONCE() as there is no need to
> crash the system in this scenario and instead we could just warn
> and fail the allocation.
>
> Fixes: 26a8ea80929c ("mm/hugetlb: fix memfd_pin_folios resv_huge_pages leak")
> Reported-by: syzbot+a504cb5bae4fe117ba94 at syzkaller.appspotmail.com
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy at intel.com>
> Cc: Steve Sistare <steven.sistare at oracle.com>
> Cc: Muchun Song <muchun.song at linux.dev>
> Cc: David Hildenbrand <david at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> ---
> include/linux/hugetlb.h | 5 +++++
> mm/hugetlb.c | 14 ++++++--------
> mm/memfd.c | 14 +++++++++++---
> 3 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index ae4fe8615bb6..38c580548564 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -712,6 +712,11 @@ extern unsigned int default_hstate_idx;
>
> #define default_hstate (hstates[default_hstate_idx])
>
> +static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
> +{
> + return HUGETLBFS_SB(inode->i_sb)->spool;
> +}
> +
> static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio)
> {
> return folio->_hugetlb_subpool;
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index c498874a7170..ef948f56b864 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -251,11 +251,6 @@ static long hugepage_subpool_put_pages(struct hugepage_subpool *spool,
> return ret;
> }
>
> -static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
> -{
> - return HUGETLBFS_SB(inode->i_sb)->spool;
> -}
> -
> static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
> {
> return subpool_inode(file_inode(vma->vm_file));
> @@ -2397,12 +2392,15 @@ struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid,
> struct folio *folio;
>
> spin_lock_irq(&hugetlb_lock);
> + if (WARN_ON_ONCE(!h->resv_huge_pages)) {
> + spin_unlock_irq(&hugetlb_lock);
> + return NULL;
> + }
> +
> folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask, preferred_nid,
> nmask);
> - if (folio) {
> - VM_BUG_ON(!h->resv_huge_pages);
> + if (folio)
> h->resv_huge_pages--;
> - }
>
> spin_unlock_irq(&hugetlb_lock);
> return folio;
> diff --git a/mm/memfd.c b/mm/memfd.c
> index 35a370d75c9a..0d128c44fb78 100644
> --- a/mm/memfd.c
> +++ b/mm/memfd.c
> @@ -70,7 +70,7 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
> #ifdef CONFIG_HUGETLB_PAGE
> struct folio *folio;
> gfp_t gfp_mask;
> - int err;
> + int err = -ENOMEM;
>
> if (is_file_hugepages(memfd)) {
> /*
> @@ -79,12 +79,16 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
> * alloc from. Also, the folio will be pinned for an indefinite
> * amount of time, so it is not expected to be migrated away.
> */
> + struct inode *inode = file_inode(memfd);
> struct hstate *h = hstate_file(memfd);
>
> gfp_mask = htlb_alloc_mask(h);
> gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
> idx >>= huge_page_order(h);
>
> + if (!hugetlb_reserve_pages(inode, idx, idx + 1, NULL, 0))
> + return ERR_PTR(err);
> +
> folio = alloc_hugetlb_folio_reserve(h,
> numa_node_id(),
> NULL,
> @@ -95,12 +99,16 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
> idx);
> if (err) {
> folio_put(folio);
> - return ERR_PTR(err);
> + goto err;
> }
> +
> + hugetlb_set_folio_subpool(folio, subpool_inode(inode));
> folio_unlock(folio);
> return folio;
> }
> - return ERR_PTR(-ENOMEM);
> +err:
> + hugetlb_unreserve_pages(inode, idx, idx + 1, 0);
Hmmm, shouldn't we maybe only un-reserve if we were responsible for the
reservation above?
If it's already reserved before this call, we should probably leave it
as is?
Or maybe we never want to un-reserve at all here?
--
Cheers,
David / dhildenb
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