The patch titled Subject: mm: fix __wp_page_copy_user fallback path for remote mm has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-fix-__wp_page_copy_user-fallback-path-for-remote-mm.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Asahi Lina lina@asahilina.net Subject: mm: fix __wp_page_copy_user fallback path for remote mm Date: Fri, 01 Nov 2024 21:08:02 +0900

If the source page is a PFN mapping, we copy back from userspace. However, if this fault is a remote access, we cannot use __copy_from_user_inatomic. Instead, use access_remote_vm() in this case.

Fixes WARN and incorrect zero-filling when writing to CoW mappings in a remote process, such as when using gdb on a binary present on a DAX filesystem.

[ 143.683782] ------------[ cut here ]------------ [ 143.683784] WARNING: CPU: 1 PID: 350 at mm/memory.c:2904 __wp_page_copy_user+0x120/0x2bc [ 143.683793] CPU: 1 PID: 350 Comm: gdb Not tainted 6.6.52 #1 [ 143.683794] Hardware name: linux,dummy-virt (DT) [ 143.683795] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) [ 143.683796] pc : __wp_page_copy_user+0x120/0x2bc [ 143.683798] lr : __wp_page_copy_user+0x254/0x2bc [ 143.683799] sp : ffff80008272b8b0 [ 143.683799] x29: ffff80008272b8b0 x28: 0000000000000000 x27: ffff000083bad580 [ 143.683801] x26: 0000000000000000 x25: 0000fffff7fd5000 x24: ffff000081db04c0 [ 143.683802] x23: ffff00014f24b000 x22: fffffc00053c92c0 x21: ffff000083502150 [ 143.683803] x20: 0000fffff7fd5000 x19: ffff80008272b9d0 x18: 0000000000000000 [ 143.683804] x17: ffff000081db0500 x16: ffff800080fe52a0 x15: 0000fffff7fd5000 [ 143.683804] x14: 0000000000bb1845 x13: 0000000000000080 x12: ffff80008272b880 [ 143.683805] x11: ffff000081d13600 x10: ffff000081d13608 x9 : ffff000081d1360c [ 143.683806] x8 : ffff000083a16f00 x7 : 0000000000000010 x6 : ffff00014f24b000 [ 143.683807] x5 : ffff00014f24c000 x4 : 0000000000000000 x3 : ffff000083582000 [ 143.683807] x2 : 0000000000000f80 x1 : 0000fffff7fd5000 x0 : 0000000000001000 [ 143.683808] Call trace: [ 143.683809] __wp_page_copy_user+0x120/0x2bc [ 143.683810] wp_page_copy+0x98/0x5c0 [ 143.683813] do_wp_page+0x250/0x530 [ 143.683814] __handle_mm_fault+0x278/0x284 [ 143.683817] handle_mm_fault+0x64/0x1e8 [ 143.683819] faultin_page+0x5c/0x110 [ 143.683820] __get_user_pages+0xc8/0x2f4 [ 143.683821] get_user_pages_remote+0xac/0x30c [ 143.683823] __access_remote_vm+0xb4/0x368 [ 143.683824] access_remote_vm+0x10/0x1c [ 143.683826] mem_rw.isra.0+0xc4/0x218 [ 143.683831] mem_write+0x18/0x24 [ 143.683831] vfs_write+0xa0/0x37c [ 143.683834] ksys_pwrite64+0x7c/0xc0 [ 143.683834] __arm64_sys_pwrite64+0x20/0x2c [ 143.683835] invoke_syscall+0x48/0x10c [ 143.683837] el0_svc_common.constprop.0+0x40/0xe0 [ 143.683839] do_el0_svc+0x1c/0x28 [ 143.683841] el0_svc+0x3c/0xdc [ 143.683846] el0t_64_sync_handler+0x120/0x12c [ 143.683848] el0t_64_sync+0x194/0x198 [ 143.683849] ---[ end trace 0000000000000000 ]---

Link: https://lkml.kernel.org/r/20241101-mm-remote-pfn-v1-1-080b609270b7@asahilina... Fixes: 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF is cleared") Signed-off-by: Asahi Lina lina@asahilina.net Cc: Jia He justin.he@arm.com Cc: Yibo Cai Yibo.Cai@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Asahi Lina lina@asahilina.net Cc: Sergio Lopez Pascual slp@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/mm/memory.c~mm-fix-__wp_page_copy_user-fallback-path-for-remote-mm +++ a/mm/memory.c @@ -3081,13 +3081,18 @@ static inline int __wp_page_copy_user(st update_mmu_cache_range(vmf, vma, addr, vmf->pte, 1); }

+ /* If the mm is a remote mm, copy in the page using access_remote_vm() */ + if (current->mm != mm) { + if (access_remote_vm(mm, (unsigned long)uaddr, kaddr, PAGE_SIZE, 0) != PAGE_SIZE) + goto warn; + } /* * This really shouldn't fail, because the page is there * in the page tables. But it might just be unreadable, * in which case we just give up and fill the result with * zeroes. */ - if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { + else if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { if (vmf->pte) goto warn;

_

Patches currently in -mm which might be from lina@asahilina.net are

mm-fix-__wp_page_copy_user-fallback-path-for-remote-mm.patch