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Message-ID: <12f75bbf-aab1-4c2a-92ac-268da81250d6@lucifer.local>
Date: Wed, 7 Aug 2024 09:07:48 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Pengfei Xu <pengfei.xu@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, Matthew Wilcox <willy@...radead.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>, SeongJae Park <sj@...nel.org>,
Shuah Khan <shuah@...nel.org>,
Brendan Higgins <brendanhiggins@...gle.com>,
David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH v4 1/7] userfaultfd: move core VMA manipulation logic to
mm/userfaultfd.c
On Wed, Aug 07, 2024 at 11:45:56AM GMT, Pengfei Xu wrote:
> Hi Lorenzo Stoakes,
>
> Greetings!
>
> I used syzkaller and found
> KASAN: slab-use-after-free Read in userfaultfd_set_ctx in next-20240805.
>
> Bisected the first bad commit:
> 4651ba8201cf userfaultfd: move core VMA manipulation logic to mm/userfaultfd.c
Hi,
Thanks for this, I will investigate as a priority and work up a fix. As it's
simply a refactor I suspect this should be relatively straightforward.
>
> All detailed info: https://github.com/xupengfe/syzkaller_logs/tree/main/240806_122723_userfaultfd_set_ctx
> Syzkaller repro code: https://github.com/xupengfe/syzkaller_logs/blob/main/240806_122723_userfaultfd_set_ctx/repro.c
> Syzkaller repro syscall steps: https://github.com/xupengfe/syzkaller_logs/blob/main/240806_122723_userfaultfd_set_ctx/repro.prog
> Syzkaller analysis report: https://github.com/xupengfe/syzkaller_logs/blob/main/240806_122723_userfaultfd_set_ctx/repro.report
> Kconfig(make olddefconfig): https://github.com/xupengfe/syzkaller_logs/blob/main/240806_122723_userfaultfd_set_ctx/kconfig_origin
> Bisect info: https://github.com/xupengfe/syzkaller_logs/blob/main/240806_122723_userfaultfd_set_ctx/bisect_info.log
> Dmesg: https://github.com/xupengfe/syzkaller_logs/blob/main/240806_122723_userfaultfd_set_ctx/d6dbc9f56c3a70e915625b6f1887882c23dc5c91_dmesg.log
> bzImage: https://github.com/xupengfe/syzkaller_logs/raw/main/240806_122723_userfaultfd_set_ctx/bzImage_d6dbc9f56c3a70e915625b6f1887882c23dc5c91.tar.gz
>
> "
> [ 29.675551] ==================================================================
> [ 29.676133] BUG: KASAN: slab-use-after-free in userfaultfd_set_ctx+0x31c/0x360
> [ 29.676716] Read of size 8 at addr ffff888027c5f100 by task repro/1498
> [ 29.677218]
> [ 29.677358] CPU: 0 UID: 0 PID: 1498 Comm: repro Not tainted 6.11.0-rc2-next-20240805-d6dbc9f56c3a #1
> [ 29.678053] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> [ 29.678910] Call Trace:
> [ 29.679117] <TASK>
> [ 29.679296] dump_stack_lvl+0xea/0x150
> [ 29.679622] print_report+0xce/0x610
> [ 29.679924] ? userfaultfd_set_ctx+0x31c/0x360
> [ 29.680289] ? kasan_complete_mode_report_info+0x80/0x200
> [ 29.680716] ? userfaultfd_set_ctx+0x31c/0x360
> [ 29.681077] kasan_report+0xcc/0x110
> [ 29.681372] ? userfaultfd_set_ctx+0x31c/0x360
> [ 29.681729] __asan_report_load8_noabort+0x18/0x20
> [ 29.682118] userfaultfd_set_ctx+0x31c/0x360
> [ 29.682465] userfaultfd_clear_vma+0x104/0x190
> [ 29.682826] userfaultfd_release_all+0x294/0x4a0
> [ 29.683201] ? __pfx_userfaultfd_release_all+0x10/0x10
> [ 29.683615] ? __this_cpu_preempt_check+0x21/0x30
> [ 29.684003] ? __pfx_userfaultfd_release+0x10/0x10
> [ 29.684389] userfaultfd_release+0x112/0x1e0
> [ 29.684735] ? __pfx_userfaultfd_release+0x10/0x10
> [ 29.685114] ? evm_file_release+0x193/0x1f0
> [ 29.685454] __fput+0x426/0xbc0
> [ 29.685719] ? __sanitizer_cov_trace_const_cmp2+0x1c/0x30
> [ 29.686153] __fput_sync+0x58/0x70
> [ 29.686435] __x64_sys_close+0x93/0x120
> [ 29.686744] x64_sys_call+0x189a/0x20d0
> [ 29.687066] do_syscall_64+0x6d/0x140
> [ 29.687371] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 29.687779] RIP: 0033:0x7f3b67b3f247
> [ 29.688078] Code: ff e8 cd e3 01 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 41 c3 48 83 ec 18 89 7c 24 0c e8 c3 c9 f5 ff
> [ 29.689519] RSP: 002b:00007ffd1f0ac7d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
> [ 29.690140] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3b67b3f247
> [ 29.690717] RDX: 0000000020000100 RSI: 000000008010aa01 RDI: 0000000000000003
> [ 29.691270] RBP: 00007ffd1f0ac7f0 R08: 00007ffd1f0ac7f0 R09: 00007ffd1f0ac7f0
> [ 29.691822] R10: 00007ffd1f0ac7f0 R11: 0000000000000246 R12: 00007ffd1f0ac968
> [ 29.692375] R13: 0000000000401bf9 R14: 0000000000403e08 R15: 00007f3b67c72000
> [ 29.692939] </TASK>
> [ 29.693124]
> [ 29.693258] Allocated by task 1498:
> [ 29.693545] kasan_save_stack+0x2c/0x60
> [ 29.693875] kasan_save_track+0x18/0x40
> [ 29.694205] kasan_save_alloc_info+0x3c/0x50
> [ 29.694576] __kasan_slab_alloc+0x62/0x80
> [ 29.694921] kmem_cache_alloc_noprof+0x114/0x370
> [ 29.695319] vm_area_dup+0x2a/0x1b0
> [ 29.695630] __split_vma+0x188/0x1020
> [ 29.695952] vma_modify+0x1fc/0x390
> [ 29.696250] userfaultfd_clear_vma+0xd4/0x190
> [ 29.696609] userfaultfd_ioctl+0x3c0b/0x4560
> [ 29.696964] __x64_sys_ioctl+0x1b9/0x230
> [ 29.697295] x64_sys_call+0x1209/0x20d0
> [ 29.697620] do_syscall_64+0x6d/0x140
> [ 29.697937] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 29.698364]
> [ 29.698508] Freed by task 1505:
> [ 29.698779] kasan_save_stack+0x2c/0x60
> [ 29.699110] kasan_save_track+0x18/0x40
> [ 29.699441] kasan_save_free_info+0x3f/0x60
> [ 29.699797] __kasan_slab_free+0x47/0x60
> [ 29.700137] kmem_cache_free+0x2f2/0x4b0
> [ 29.700471] vm_area_free_rcu_cb+0x7f/0xa0
> [ 29.700819] rcu_core+0x877/0x18f0
> [ 29.701123] rcu_core_si+0x12/0x20
> [ 29.701421] handle_softirqs+0x1c7/0x870
> [ 29.701760] __irq_exit_rcu+0xa9/0x120
> [ 29.702082] irq_exit_rcu+0x12/0x30
> [ 29.702386] sysvec_apic_timer_interrupt+0xa5/0xc0
> [ 29.702802] asm_sysvec_apic_timer_interrupt+0x1f/0x30
> [ 29.703237]
> [ 29.703377] Last potentially related work creation:
> [ 29.703782] kasan_save_stack+0x2c/0x60
> [ 29.704114] __kasan_record_aux_stack+0x93/0xb0
> [ 29.704503] kasan_record_aux_stack_noalloc+0xf/0x20
> [ 29.704923] __call_rcu_common.constprop.0+0x72/0x6b0
> [ 29.705349] call_rcu+0x12/0x20
> [ 29.705625] vm_area_free+0x26/0x30
> [ 29.705928] vma_complete+0x57e/0xf60
> [ 29.706245] vma_merge+0x166b/0x3540
> [ 29.706555] vma_modify+0x9f/0x390
> [ 29.706853] userfaultfd_clear_vma+0xd4/0x190
> [ 29.707227] userfaultfd_release_all+0x294/0x4a0
> [ 29.707621] userfaultfd_release+0x112/0x1e0
> [ 29.707991] __fput+0x426/0xbc0
> [ 29.708267] __fput_sync+0x58/0x70
> [ 29.708563] __x64_sys_close+0x93/0x120
> [ 29.708891] x64_sys_call+0x189a/0x20d0
> [ 29.709220] do_syscall_64+0x6d/0x140
> [ 29.709538] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 29.709965]
> [ 29.710105] The buggy address belongs to the object at ffff888027c5f0f0
> [ 29.710105] which belongs to the cache vm_area_struct of size 176
> [ 29.711130] The buggy address is located 16 bytes inside of
> [ 29.711130] freed 176-byte region [ffff888027c5f0f0, ffff888027c5f1a0)
> [ 29.712104]
> [ 29.712245] The buggy address belongs to the physical page:
> [ 29.712703] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x27c5f
> [ 29.713349] memcg:ffff8880198eaa01
> [ 29.713639] flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)
> [ 29.714173] page_type: 0xfdffffff(slab)
> [ 29.714507] raw: 000fffffc0000000 ffff88800d319dc0 dead000000000122 0000000000000000
> [ 29.715137] raw: 0000000000000000 0000000000110011 00000001fdffffff ffff8880198eaa01
> [ 29.715765] page dumped because: kasan: bad access detected
> [ 29.716220]
> [ 29.716360] Memory state around the buggy address:
> [ 29.716756] ffff888027c5f000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [ 29.717349] ffff888027c5f080: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fa fb
> [ 29.717940] >ffff888027c5f100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 29.718521] ^
> [ 29.718796] ffff888027c5f180: fb fb fb fb fc fc fc fc fc fc fc fc 00 00 00 00
> [ 29.719388] ffff888027c5f200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [ 29.720025] ==================================================================
> [ 29.720671] Disabling lock debugging due to kernel taint
> "
>
> Thanks!
>
> ---
>
> If you don't need the following environment to reproduce the problem or if you
> already have one reproduced environment, please ignore the following information.
>
> How to reproduce:
> git clone https://gitlab.com/xupengfe/repro_vm_env.git
> cd repro_vm_env
> tar -xvf repro_vm_env.tar.gz
> cd repro_vm_env; ./start3.sh // it needs qemu-system-x86_64 and I used v7.1.0
> // start3.sh will load bzImage_2241ab53cbb5cdb08a6b2d4688feb13971058f65 v6.2-rc5 kernel
> // You could change the bzImage_xxx as you want
> // Maybe you need to remove line "-drive if=pflash,format=raw,readonly=on,file=./OVMF_CODE.fd \" for different qemu version
> You could use below command to log in, there is no password for root.
> ssh -p 10023 root@...alhost
>
> After login vm(virtual machine) successfully, you could transfer reproduced
> binary to the vm by below way, and reproduce the problem in vm:
> gcc -pthread -o repro repro.c
> scp -P 10023 repro root@...alhost:/root/
>
> Get the bzImage for target kernel:
> Please use target kconfig and copy it to kernel_src/.config
> make olddefconfig
> make -jx bzImage //x should equal or less than cpu num your pc has
>
> Fill the bzImage file into above start3.sh to load the target kernel in vm.
>
>
> Tips:
> If you already have qemu-system-x86_64, please ignore below info.
> If you want to install qemu v7.1.0 version:
> git clone https://github.com/qemu/qemu.git
> cd qemu
> git checkout -f v7.1.0
> mkdir build
> cd build
> yum install -y ninja-build.x86_64
> yum -y install libslirp-devel.x86_64
> ../configure --target-list=x86_64-softmmu --enable-kvm --enable-vnc --enable-gtk --enable-sdl --enable-usb-redir --enable-slirp
> make
> make install
>
> Best Regards,
> Thanks!
>
>
> On 2024-07-29 at 12:50:35 +0100, Lorenzo Stoakes wrote:
> > This patch forms part of a patch series intending to separate out VMA logic
> > and render it testable from userspace, which requires that core
> > manipulation functions be exposed in an mm/-internal header file.
> >
> > In order to do this, we must abstract APIs we wish to test, in this
> > instance functions which ultimately invoke vma_modify().
> >
> > This patch therefore moves all logic which ultimately invokes vma_modify()
> > to mm/userfaultfd.c, trying to transfer code at a functional granularity
> > where possible.
> >
> > Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> > Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > ---
> > fs/userfaultfd.c | 160 +++-----------------------------
> > include/linux/userfaultfd_k.h | 19 ++++
> > mm/userfaultfd.c | 168 ++++++++++++++++++++++++++++++++++
> > 3 files changed, 198 insertions(+), 149 deletions(-)
> >
> > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > index 27a3e9285fbf..b3ed7207df7e 100644
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -104,21 +104,6 @@ bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
> > return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
> > }
> >
> > -static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
> > - vm_flags_t flags)
> > -{
> > - const bool uffd_wp_changed = (vma->vm_flags ^ flags) & VM_UFFD_WP;
> > -
> > - vm_flags_reset(vma, flags);
> > - /*
> > - * For shared mappings, we want to enable writenotify while
> > - * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
> > - * recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
> > - */
> > - if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
> > - vma_set_page_prot(vma);
> > -}
> > -
> > static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
> > int wake_flags, void *key)
> > {
> > @@ -615,22 +600,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> > spin_unlock_irq(&ctx->event_wqh.lock);
> >
> > if (release_new_ctx) {
> > - struct vm_area_struct *vma;
> > - struct mm_struct *mm = release_new_ctx->mm;
> > - VMA_ITERATOR(vmi, mm, 0);
> > -
> > - /* the various vma->vm_userfaultfd_ctx still points to it */
> > - mmap_write_lock(mm);
> > - for_each_vma(vmi, vma) {
> > - if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
> > - vma_start_write(vma);
> > - vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > - userfaultfd_set_vm_flags(vma,
> > - vma->vm_flags & ~__VM_UFFD_FLAGS);
> > - }
> > - }
> > - mmap_write_unlock(mm);
> > -
> > + userfaultfd_release_new(release_new_ctx);
> > userfaultfd_ctx_put(release_new_ctx);
> > }
> >
> > @@ -662,9 +632,7 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
> > return 0;
> >
> > if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) {
> > - vma_start_write(vma);
> > - vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > - userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS);
> > + userfaultfd_reset_ctx(vma);
> > return 0;
> > }
> >
> > @@ -749,9 +717,7 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
> > up_write(&ctx->map_changing_lock);
> > } else {
> > /* Drop uffd context if remap feature not enabled */
> > - vma_start_write(vma);
> > - vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > - userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS);
> > + userfaultfd_reset_ctx(vma);
> > }
> > }
> >
> > @@ -870,53 +836,13 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> > {
> > struct userfaultfd_ctx *ctx = file->private_data;
> > struct mm_struct *mm = ctx->mm;
> > - struct vm_area_struct *vma, *prev;
> > /* len == 0 means wake all */
> > struct userfaultfd_wake_range range = { .len = 0, };
> > - unsigned long new_flags;
> > - VMA_ITERATOR(vmi, mm, 0);
> >
> > WRITE_ONCE(ctx->released, true);
> >
> > - if (!mmget_not_zero(mm))
> > - goto wakeup;
> > -
> > - /*
> > - * Flush page faults out of all CPUs. NOTE: all page faults
> > - * must be retried without returning VM_FAULT_SIGBUS if
> > - * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
> > - * changes while handle_userfault released the mmap_lock. So
> > - * it's critical that released is set to true (above), before
> > - * taking the mmap_lock for writing.
> > - */
> > - mmap_write_lock(mm);
> > - prev = NULL;
> > - for_each_vma(vmi, vma) {
> > - cond_resched();
> > - BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
> > - !!(vma->vm_flags & __VM_UFFD_FLAGS));
> > - if (vma->vm_userfaultfd_ctx.ctx != ctx) {
> > - prev = vma;
> > - continue;
> > - }
> > - /* Reset ptes for the whole vma range if wr-protected */
> > - if (userfaultfd_wp(vma))
> > - uffd_wp_range(vma, vma->vm_start,
> > - vma->vm_end - vma->vm_start, false);
> > - new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
> > - vma = vma_modify_flags_uffd(&vmi, prev, vma, vma->vm_start,
> > - vma->vm_end, new_flags,
> > - NULL_VM_UFFD_CTX);
> > -
> > - vma_start_write(vma);
> > - userfaultfd_set_vm_flags(vma, new_flags);
> > - vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > + userfaultfd_release_all(mm, ctx);
> >
> > - prev = vma;
> > - }
> > - mmap_write_unlock(mm);
> > - mmput(mm);
> > -wakeup:
> > /*
> > * After no new page faults can wait on this fault_*wqh, flush
> > * the last page faults that may have been already waiting on
> > @@ -1293,14 +1219,14 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > unsigned long arg)
> > {
> > struct mm_struct *mm = ctx->mm;
> > - struct vm_area_struct *vma, *prev, *cur;
> > + struct vm_area_struct *vma, *cur;
> > int ret;
> > struct uffdio_register uffdio_register;
> > struct uffdio_register __user *user_uffdio_register;
> > - unsigned long vm_flags, new_flags;
> > + unsigned long vm_flags;
> > bool found;
> > bool basic_ioctls;
> > - unsigned long start, end, vma_end;
> > + unsigned long start, end;
> > struct vma_iterator vmi;
> > bool wp_async = userfaultfd_wp_async_ctx(ctx);
> >
> > @@ -1428,57 +1354,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > } for_each_vma_range(vmi, cur, end);
> > BUG_ON(!found);
> >
> > - vma_iter_set(&vmi, start);
> > - prev = vma_prev(&vmi);
> > - if (vma->vm_start < start)
> > - prev = vma;
> > -
> > - ret = 0;
> > - for_each_vma_range(vmi, vma, end) {
> > - cond_resched();
> > -
> > - BUG_ON(!vma_can_userfault(vma, vm_flags, wp_async));
> > - BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
> > - vma->vm_userfaultfd_ctx.ctx != ctx);
> > - WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
> > -
> > - /*
> > - * Nothing to do: this vma is already registered into this
> > - * userfaultfd and with the right tracking mode too.
> > - */
> > - if (vma->vm_userfaultfd_ctx.ctx == ctx &&
> > - (vma->vm_flags & vm_flags) == vm_flags)
> > - goto skip;
> > -
> > - if (vma->vm_start > start)
> > - start = vma->vm_start;
> > - vma_end = min(end, vma->vm_end);
> > -
> > - new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
> > - vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
> > - new_flags,
> > - (struct vm_userfaultfd_ctx){ctx});
> > - if (IS_ERR(vma)) {
> > - ret = PTR_ERR(vma);
> > - break;
> > - }
> > -
> > - /*
> > - * In the vma_merge() successful mprotect-like case 8:
> > - * the next vma was merged into the current one and
> > - * the current one has not been updated yet.
> > - */
> > - vma_start_write(vma);
> > - userfaultfd_set_vm_flags(vma, new_flags);
> > - vma->vm_userfaultfd_ctx.ctx = ctx;
> > -
> > - if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
> > - hugetlb_unshare_all_pmds(vma);
> > -
> > - skip:
> > - prev = vma;
> > - start = vma->vm_end;
> > - }
> > + ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end,
> > + wp_async);
> >
> > out_unlock:
> > mmap_write_unlock(mm);
> > @@ -1519,7 +1396,6 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > struct vm_area_struct *vma, *prev, *cur;
> > int ret;
> > struct uffdio_range uffdio_unregister;
> > - unsigned long new_flags;
> > bool found;
> > unsigned long start, end, vma_end;
> > const void __user *buf = (void __user *)arg;
> > @@ -1622,27 +1498,13 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
> > }
> >
> > - /* Reset ptes for the whole vma range if wr-protected */
> > - if (userfaultfd_wp(vma))
> > - uffd_wp_range(vma, start, vma_end - start, false);
> > -
> > - new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
> > - vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
> > - new_flags, NULL_VM_UFFD_CTX);
> > + vma = userfaultfd_clear_vma(&vmi, prev, vma,
> > + start, vma_end);
> > if (IS_ERR(vma)) {
> > ret = PTR_ERR(vma);
> > break;
> > }
> >
> > - /*
> > - * In the vma_merge() successful mprotect-like case 8:
> > - * the next vma was merged into the current one and
> > - * the current one has not been updated yet.
> > - */
> > - vma_start_write(vma);
> > - userfaultfd_set_vm_flags(vma, new_flags);
> > - vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > -
> > skip:
> > prev = vma;
> > start = vma->vm_end;
> > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
> > index a12bcf042551..9fc6ce15c499 100644
> > --- a/include/linux/userfaultfd_k.h
> > +++ b/include/linux/userfaultfd_k.h
> > @@ -267,6 +267,25 @@ extern void userfaultfd_unmap_complete(struct mm_struct *mm,
> > extern bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma);
> > extern bool userfaultfd_wp_async(struct vm_area_struct *vma);
> >
> > +void userfaultfd_reset_ctx(struct vm_area_struct *vma);
> > +
> > +struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
> > + struct vm_area_struct *prev,
> > + struct vm_area_struct *vma,
> > + unsigned long start,
> > + unsigned long end);
> > +
> > +int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
> > + struct vm_area_struct *vma,
> > + unsigned long vm_flags,
> > + unsigned long start, unsigned long end,
> > + bool wp_async);
> > +
> > +void userfaultfd_release_new(struct userfaultfd_ctx *ctx);
> > +
> > +void userfaultfd_release_all(struct mm_struct *mm,
> > + struct userfaultfd_ctx *ctx);
> > +
> > #else /* CONFIG_USERFAULTFD */
> >
> > /* mm helpers */
> > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> > index e54e5c8907fa..3b7715ecf292 100644
> > --- a/mm/userfaultfd.c
> > +++ b/mm/userfaultfd.c
> > @@ -1760,3 +1760,171 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
> > VM_WARN_ON(!moved && !err);
> > return moved ? moved : err;
> > }
> > +
> > +static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
> > + vm_flags_t flags)
> > +{
> > + const bool uffd_wp_changed = (vma->vm_flags ^ flags) & VM_UFFD_WP;
> > +
> > + vm_flags_reset(vma, flags);
> > + /*
> > + * For shared mappings, we want to enable writenotify while
> > + * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
> > + * recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
> > + */
> > + if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
> > + vma_set_page_prot(vma);
> > +}
> > +
> > +static void userfaultfd_set_ctx(struct vm_area_struct *vma,
> > + struct userfaultfd_ctx *ctx,
> > + unsigned long flags)
> > +{
> > + vma_start_write(vma);
> > + vma->vm_userfaultfd_ctx = (struct vm_userfaultfd_ctx){ctx};
> > + userfaultfd_set_vm_flags(vma,
> > + (vma->vm_flags & ~__VM_UFFD_FLAGS) | flags);
> > +}
> > +
> > +void userfaultfd_reset_ctx(struct vm_area_struct *vma)
> > +{
> > + userfaultfd_set_ctx(vma, NULL, 0);
> > +}
> > +
> > +struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
> > + struct vm_area_struct *prev,
> > + struct vm_area_struct *vma,
> > + unsigned long start,
> > + unsigned long end)
> > +{
> > + struct vm_area_struct *ret;
> > +
> > + /* Reset ptes for the whole vma range if wr-protected */
> > + if (userfaultfd_wp(vma))
> > + uffd_wp_range(vma, start, end - start, false);
> > +
> > + ret = vma_modify_flags_uffd(vmi, prev, vma, start, end,
> > + vma->vm_flags & ~__VM_UFFD_FLAGS,
> > + NULL_VM_UFFD_CTX);
> > +
> > + /*
> > + * In the vma_merge() successful mprotect-like case 8:
> > + * the next vma was merged into the current one and
> > + * the current one has not been updated yet.
> > + */
> > + if (!IS_ERR(ret))
> > + userfaultfd_reset_ctx(vma);
> > +
> > + return ret;
> > +}
> > +
> > +/* Assumes mmap write lock taken, and mm_struct pinned. */
> > +int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
> > + struct vm_area_struct *vma,
> > + unsigned long vm_flags,
> > + unsigned long start, unsigned long end,
> > + bool wp_async)
> > +{
> > + VMA_ITERATOR(vmi, ctx->mm, start);
> > + struct vm_area_struct *prev = vma_prev(&vmi);
> > + unsigned long vma_end;
> > + unsigned long new_flags;
> > +
> > + if (vma->vm_start < start)
> > + prev = vma;
> > +
> > + for_each_vma_range(vmi, vma, end) {
> > + cond_resched();
> > +
> > + BUG_ON(!vma_can_userfault(vma, vm_flags, wp_async));
> > + BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
> > + vma->vm_userfaultfd_ctx.ctx != ctx);
> > + WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
> > +
> > + /*
> > + * Nothing to do: this vma is already registered into this
> > + * userfaultfd and with the right tracking mode too.
> > + */
> > + if (vma->vm_userfaultfd_ctx.ctx == ctx &&
> > + (vma->vm_flags & vm_flags) == vm_flags)
> > + goto skip;
> > +
> > + if (vma->vm_start > start)
> > + start = vma->vm_start;
> > + vma_end = min(end, vma->vm_end);
> > +
> > + new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
> > + vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
> > + new_flags,
> > + (struct vm_userfaultfd_ctx){ctx});
> > + if (IS_ERR(vma))
> > + return PTR_ERR(vma);
> > +
> > + /*
> > + * In the vma_merge() successful mprotect-like case 8:
> > + * the next vma was merged into the current one and
> > + * the current one has not been updated yet.
> > + */
> > + userfaultfd_set_ctx(vma, ctx, vm_flags);
> > +
> > + if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
> > + hugetlb_unshare_all_pmds(vma);
> > +
> > +skip:
> > + prev = vma;
> > + start = vma->vm_end;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +void userfaultfd_release_new(struct userfaultfd_ctx *ctx)
> > +{
> > + struct mm_struct *mm = ctx->mm;
> > + struct vm_area_struct *vma;
> > + VMA_ITERATOR(vmi, mm, 0);
> > +
> > + /* the various vma->vm_userfaultfd_ctx still points to it */
> > + mmap_write_lock(mm);
> > + for_each_vma(vmi, vma) {
> > + if (vma->vm_userfaultfd_ctx.ctx == ctx)
> > + userfaultfd_reset_ctx(vma);
> > + }
> > + mmap_write_unlock(mm);
> > +}
> > +
> > +void userfaultfd_release_all(struct mm_struct *mm,
> > + struct userfaultfd_ctx *ctx)
> > +{
> > + struct vm_area_struct *vma, *prev;
> > + VMA_ITERATOR(vmi, mm, 0);
> > +
> > + if (!mmget_not_zero(mm))
> > + return;
> > +
> > + /*
> > + * Flush page faults out of all CPUs. NOTE: all page faults
> > + * must be retried without returning VM_FAULT_SIGBUS if
> > + * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
> > + * changes while handle_userfault released the mmap_lock. So
> > + * it's critical that released is set to true (above), before
> > + * taking the mmap_lock for writing.
> > + */
> > + mmap_write_lock(mm);
> > + prev = NULL;
> > + for_each_vma(vmi, vma) {
> > + cond_resched();
> > + BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
> > + !!(vma->vm_flags & __VM_UFFD_FLAGS));
> > + if (vma->vm_userfaultfd_ctx.ctx != ctx) {
> > + prev = vma;
> > + continue;
> > + }
> > +
> > + vma = userfaultfd_clear_vma(&vmi, prev, vma,
> > + vma->vm_start, vma->vm_end);
> > + prev = vma;
> > + }
> > + mmap_write_unlock(mm);
> > + mmput(mm);
> > +}
> > --
> > 2.45.2
> >
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