Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210902231813.3597709-1-surenb@google.com> <20210902231813.3597709-2-surenb@google.com>
 <202109031420.2F17A2C9@keescook>
In-Reply-To: <202109031420.2F17A2C9@keescook>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Fri, 3 Sep 2021 14:51:16 -0700
Message-ID: <CAJuCfpHLmNXhUkKg2OPV--5upP_njdrUkXDkYMMgVmABm8bd3g@mail.gmail.com>
Subject: Re: [PATCH v9 2/3] mm: add a field to store names for private
 anonymous memory
To:     Kees Cook <keescook@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Colin Cross <ccross@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Michal Hocko <mhocko@suse.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Randy Dunlap <rdunlap@infradead.org>,
        Kalesh Singh <kaleshsingh@google.com>,
        Peter Xu <peterx@redhat.com>, rppt@kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        vincenzo.frascino@arm.com,
        =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= 
        <chinwen.chang@mediatek.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Jann Horn <jannh@google.com>, apopple@nvidia.com,
        John Hubbard <jhubbard@nvidia.com>,
        Yu Zhao <yuzhao@google.com>, Will Deacon <will@kernel.org>,
        fenghua.yu@intel.com, thunder.leizhen@huawei.com,
        Hugh Dickins <hughd@google.com>, feng.tang@intel.com,
        Jason Gunthorpe <jgg@ziepe.ca>, Roman Gushchin <guro@fb.com>,
        Thomas Gleixner <tglx@linutronix.de>, krisman@collabora.com,
        chris.hyser@oracle.com, Peter Collingbourne <pcc@google.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Jens Axboe <axboe@kernel.dk>, legion@kernel.org,
        Rolf Eike Beer <eb@emlix.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Thomas Cedeno <thomascedeno@google.com>, sashal@kernel.org,
        cxfcosmos@gmail.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-mm <linux-mm@kvack.org>,
        kernel-team <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Sep 3, 2021 at 2:35 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Sep 02, 2021 at 04:18:12PM -0700, Suren Baghdasaryan wrote:
> > From: Colin Cross <ccross@google.com>
> >
> > In many userspace applications, and especially in VM based applications
> > like Android uses heavily, there are multiple different allocators in use.
> >  At a minimum there is libc malloc and the stack, and in many cases there
> > are libc malloc, the stack, direct syscalls to mmap anonymous memory, and
> > multiple VM heaps (one for small objects, one for big objects, etc.).
> > Each of these layers usually has its own tools to inspect its usage;
> > malloc by compiling a debug version, the VM through heap inspection tools,
> > and for direct syscalls there is usually no way to track them.
> >
> > On Android we heavily use a set of tools that use an extended version of
> > the logic covered in Documentation/vm/pagemap.txt to walk all pages mapped
> > in userspace and slice their usage by process, shared (COW) vs.  unique
> > mappings, backing, etc.  This can account for real physical memory usage
> > even in cases like fork without exec (which Android uses heavily to share
> > as many private COW pages as possible between processes), Kernel SamePage
> > Merging, and clean zero pages.  It produces a measurement of the pages
> > that only exist in that process (USS, for unique), and a measurement of
> > the physical memory usage of that process with the cost of shared pages
> > being evenly split between processes that share them (PSS).
> >
> > If all anonymous memory is indistinguishable then figuring out the real
> > physical memory usage (PSS) of each heap requires either a pagemap walking
> > tool that can understand the heap debugging of every layer, or for every
> > layer's heap debugging tools to implement the pagemap walking logic, in
> > which case it is hard to get a consistent view of memory across the whole
> > system.
> >
> > Tracking the information in userspace leads to all sorts of problems.
> > It either needs to be stored inside the process, which means every
> > process has to have an API to export its current heap information upon
> > request, or it has to be stored externally in a filesystem that
> > somebody needs to clean up on crashes.  It needs to be readable while
> > the process is still running, so it has to have some sort of
> > synchronization with every layer of userspace.  Efficiently tracking
> > the ranges requires reimplementing something like the kernel vma
> > trees, and linking to it from every layer of userspace.  It requires
> > more memory, more syscalls, more runtime cost, and more complexity to
> > separately track regions that the kernel is already tracking.
> >
> > This patch adds a field to /proc/pid/maps and /proc/pid/smaps to show a
> > userspace-provided name for anonymous vmas.  The names of named anonymous
> > vmas are shown in /proc/pid/maps and /proc/pid/smaps as [anon:<name>].
> >
> > Userspace can set the name for a region of memory by calling
> > prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
> > Setting the name to NULL clears it. The name length limit is 256 bytes
> > including NUL-terminator and is checked to contain only printable ascii
> > characters (including space), except '[','\' and ']'.
>
> Is the reason this isn't done via madvise() because we're forced into an
> "int" argument there? (Otherwise we could pass a pointer there.)
>
>         int madvise(void *addr, size_t length, int advice);
>

I'll need to check the original reasons this has been done with
prctl() but your guess might be correct. Also I'm not sure madvise()
would be an appropriate mechanism to set an attribute... That is not
really an "advice" but a "request".

> >
> > The name is stored in a pointer in the shared union in vm_area_struct
> > that points to a null terminated string. Anonymous vmas with the same
> > name (equivalent strings) and are otherwise mergeable will be merged.
> > The name pointers are not shared between vmas even if they contain the
> > same name. The name pointer is stored in a union with fields that are
> > only used on file-backed mappings, so it does not increase memory usage.
> >
> > The patch is based on the original patch developed by Colin Cross, more
> > specifically on its latest version [1] posted upstream by Sumit Semwal.
> > It used a userspace pointer to store vma names. In that design, name
> > pointers could be shared between vmas. However during the last upstreaming
> > attempt, Kees Cook raised concerns [2] about this approach and suggested
> > to copy the name into kernel memory space, perform validity checks [3]
> > and store as a string referenced from vm_area_struct.
> > One big concern is about fork() performance which would need to strdup
> > anonymous vma names. Dave Hansen suggested experimenting with worst-case
> > scenario of forking a process with 64k vmas having longest possible names
> > [4]. I ran this experiment on an ARM64 Android device and recorded a
> > worst-case regression of almost 40% when forking such a process. This
> > regression is addressed in the followup patch which replaces the pointer
> > to a name with a refcounted structure that allows sharing the name pointer
> > between vmas of the same name. Instead of duplicating the string during
> > fork() or when splitting a vma it increments the refcount.
> >
> > [1] https://lore.kernel.org/linux-mm/20200901161459.11772-4-sumit.semwal@linaro.org/
> > [2] https://lore.kernel.org/linux-mm/202009031031.D32EF57ED@keescook/
> > [3] https://lore.kernel.org/linux-mm/202009031022.3834F692@keescook/
> > [4] https://lore.kernel.org/linux-mm/5d0358ab-8c47-2f5f-8e43-23b89d6a8e95@intel.com/
> >
> > Changes for prctl(2) manual page (in the options section):
> >
> > PR_SET_VMA
> >       Sets an attribute specified in arg2 for virtual memory areas
> >       starting from the address specified in arg3 and spanning the
> >       size specified  in arg4. arg5 specifies the value of the attribute
> >       to be set. Note that assigning an attribute to a virtual memory
> >       area might prevent it from being merged with adjacent virtual
> >       memory areas due to the difference in that attribute's value.
> >
> >       Currently, arg2 must be one of:
> >
> >       PR_SET_VMA_ANON_NAME
> >               Set a name for anonymous virtual memory areas. arg5 should
> >               be a pointer to a null-terminated string containing the
> >               name. The name length including null byte cannot exceed
> >               256 bytes. If arg5 is NULL, the name of the appropriate
> >               anonymous virtual memory areas will be reset.
> >
> > Signed-off-by: Colin Cross <ccross@google.com>
> > [surenb: rebased over v5.14-rc7, replaced userpointer with a kernel copy
> > and added input sanitization. The bulk of the work here was done by Colin
> > Cross, therefore, with his permission, keeping him as the author]
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> > previous version including cover letter with test results is at:
> > https://lore.kernel.org/linux-mm/20210827191858.2037087-1-surenb@google.com/
> >
> > changes in v9
> > - Added documentation for prctl(2) manual page describing newly introduced
> > options, per Pavel Machek
> > - Documented the downside of naming an anonymous vma which might prevent
> > it from being merged with adjacent vmas, per Cyrill Gorcunov
> > - Replaced seq_puts+seq_write with seq_printf, per Kees Cook
> > - Changed name validation to allow only printable ascii characters, except for
> > '[', '\' and ']', per Rasmus Villemoes
> > - Added madvise_set_anon_name definition dependency on CONFIG_PROC_FS,
> > per Michal Hocko
> > - Added NULL check for the name input in prctl_set_vma to correctly handle this
> > case, per Michal Hocko
> > - Handle the possibility of kstrdup returning NULL, per Rolf Eike Beer
> > - Changed max anon vma name length from 64 to 256 (as in the original patch)
> > because I found one case of the name length being 139 bytes. If anyone is
> > curious, here it is:
> > dalvik-/data/dalvik-cache/arm64/apex@com.android.permission@priv-app@GooglePermissionController@GooglePermissionController.apk@classes.art
> >
> >  Documentation/filesystems/proc.rst |   2 +
> >  fs/proc/task_mmu.c                 |  12 ++-
> >  fs/userfaultfd.c                   |   7 +-
> >  include/linux/mm.h                 |  13 ++-
> >  include/linux/mm_types.h           |  48 ++++++++++-
> >  include/uapi/linux/prctl.h         |   3 +
> >  kernel/fork.c                      |   2 +
> >  kernel/sys.c                       |  61 ++++++++++++++
> >  mm/madvise.c                       | 131 ++++++++++++++++++++++++++---
> >  mm/mempolicy.c                     |   3 +-
> >  mm/mlock.c                         |   2 +-
> >  mm/mmap.c                          |  38 +++++----
> >  mm/mprotect.c                      |   2 +-
> >  13 files changed, 283 insertions(+), 41 deletions(-)
> >
> > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> > index 042c418f4090..a067eec54ef1 100644
> > --- a/Documentation/filesystems/proc.rst
> > +++ b/Documentation/filesystems/proc.rst
> > @@ -431,6 +431,8 @@ is not associated with a file:
> >   [stack]                    the stack of the main process
> >   [vdso]                     the "virtual dynamic shared object",
> >                              the kernel system call handler
> > +[anon:<name>]               an anonymous mapping that has been
> > +                            named by userspace
> >   =======                    ====================================
> >
> >   or if empty, the mapping is anonymous.
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index eb97468dfe4c..d41edb4b4540 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -308,6 +308,8 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
> >
> >       name = arch_vma_name(vma);
> >       if (!name) {
> > +             const char *anon_name;
> > +
> >               if (!mm) {
> >                       name = "[vdso]";
> >                       goto done;
> > @@ -319,8 +321,16 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
> >                       goto done;
> >               }
> >
> > -             if (is_stack(vma))
> > +             if (is_stack(vma)) {
> >                       name = "[stack]";
> > +                     goto done;
> > +             }
> > +
> > +             anon_name = vma_anon_name(vma);
> > +             if (anon_name) {
> > +                     seq_pad(m, ' ');
> > +                     seq_printf(m, "[anon:%s]", anon_name);
> > +             }
> >       }
> >
> >  done:
> > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > index 5c2d806e6ae5..5057843fb71a 100644
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -876,7 +876,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> >                                new_flags, vma->anon_vma,
> >                                vma->vm_file, vma->vm_pgoff,
> >                                vma_policy(vma),
> > -                              NULL_VM_UFFD_CTX);
> > +                              NULL_VM_UFFD_CTX, vma_anon_name(vma));
> >               if (prev)
> >                       vma = prev;
> >               else
> > @@ -1440,7 +1440,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> >               prev = vma_merge(mm, prev, start, vma_end, new_flags,
> >                                vma->anon_vma, vma->vm_file, vma->vm_pgoff,
> >                                vma_policy(vma),
> > -                              ((struct vm_userfaultfd_ctx){ ctx }));
> > +                              ((struct vm_userfaultfd_ctx){ ctx }),
> > +                              vma_anon_name(vma));
> >               if (prev) {
> >                       vma = prev;
> >                       goto next;
> > @@ -1617,7 +1618,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> >               prev = vma_merge(mm, prev, start, vma_end, new_flags,
> >                                vma->anon_vma, vma->vm_file, vma->vm_pgoff,
> >                                vma_policy(vma),
> > -                              NULL_VM_UFFD_CTX);
> > +                              NULL_VM_UFFD_CTX, vma_anon_name(vma));
> >               if (prev) {
> >                       vma = prev;
> >                       goto next;
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index e59646a5d44d..c72226215f33 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2550,7 +2550,7 @@ static inline int vma_adjust(struct vm_area_struct *vma, unsigned long start,
> >  extern struct vm_area_struct *vma_merge(struct mm_struct *,
> >       struct vm_area_struct *prev, unsigned long addr, unsigned long end,
> >       unsigned long vm_flags, struct anon_vma *, struct file *, pgoff_t,
> > -     struct mempolicy *, struct vm_userfaultfd_ctx);
> > +     struct mempolicy *, struct vm_userfaultfd_ctx, const char *);
> >  extern struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *);
> >  extern int __split_vma(struct mm_struct *, struct vm_area_struct *,
> >       unsigned long addr, int new_below);
> > @@ -3285,5 +3285,16 @@ static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
> >       return 0;
> >  }
> >
> > +#if defined(CONFIG_ADVISE_SYSCALLS) && defined(CONFIG_PROC_FS)
> > +int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> > +                       unsigned long len_in, const char *name);
> > +#else
> > +static inline int
> > +madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> > +                   unsigned long len_in, const char *name) {
> > +     return 0;
> > +}
> > +#endif
> > +
> >  #endif /* __KERNEL__ */
> >  #endif /* _LINUX_MM_H */
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 7f8ee09c711f..968a1d0463d8 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -350,11 +350,19 @@ struct vm_area_struct {
> >       /*
> >        * For areas with an address space and backing store,
> >        * linkage into the address_space->i_mmap interval tree.
> > +      *
> > +      * For private anonymous mappings, a pointer to a null terminated string
> > +      * containing the name given to the vma, or NULL if unnamed.
> >        */
> > -     struct {
> > -             struct rb_node rb;
> > -             unsigned long rb_subtree_last;
> > -     } shared;
> > +
> > +     union {
> > +             struct {
> > +                     struct rb_node rb;
> > +                     unsigned long rb_subtree_last;
> > +             } shared;
> > +             /* Serialized by mmap_sem. */
> > +             char *anon_name;
> > +     };
> >
> >       /*
> >        * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
> > @@ -809,4 +817,36 @@ typedef struct {
> >       unsigned long val;
> >  } swp_entry_t;
> >
> > +/*
> > + * mmap_lock should be read-locked when calling vma_anon_name() and while using
> > + * the returned pointer.
> > + */
> > +extern const char *vma_anon_name(struct vm_area_struct *vma);
> > +
> > +/*
> > + * mmap_lock should be read-locked for orig_vma->vm_mm.
> > + * mmap_lock should be write-locked for new_vma->vm_mm or new_vma should be
> > + * isolated.
> > + */
> > +extern void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> > +                           struct vm_area_struct *new_vma);
> > +
> > +/*
> > + * mmap_lock should be write-locked or vma should have been isolated under
> > + * write-locked mmap_lock protection.
> > + */
> > +extern void free_vma_anon_name(struct vm_area_struct *vma);
> > +
> > +/* mmap_lock should be read-locked */
> > +static inline bool is_same_vma_anon_name(struct vm_area_struct *vma,
> > +                                      const char *name)
> > +{
> > +     const char *vma_name = vma_anon_name(vma);
> > +
> > +     if (likely(!vma_name))
> > +             return name == NULL;
> > +
> > +     return name && !strcmp(name, vma_name);
> > +}
> > +
> >  #endif /* _LINUX_MM_TYPES_H */
> > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> > index 43bd7f713c39..4c8cbf510b2d 100644
> > --- a/include/uapi/linux/prctl.h
> > +++ b/include/uapi/linux/prctl.h
> > @@ -269,4 +269,7 @@ struct prctl_mm_map {
> >  # define PR_SCHED_CORE_SHARE_FROM    3 /* pull core_sched cookie to pid */
> >  # define PR_SCHED_CORE_MAX           4
> >
> > +#define PR_SET_VMA           0x53564d41
> > +# define PR_SET_VMA_ANON_NAME                0
> > +
> >  #endif /* _LINUX_PRCTL_H */
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 695d1343a254..cfb8c47564d8 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -366,12 +366,14 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
> >               *new = data_race(*orig);
> >               INIT_LIST_HEAD(&new->anon_vma_chain);
> >               new->vm_next = new->vm_prev = NULL;
> > +             dup_vma_anon_name(orig, new);
> >       }
> >       return new;
> >  }
> >
> >  void vm_area_free(struct vm_area_struct *vma)
> >  {
> > +     free_vma_anon_name(vma);
> >       kmem_cache_free(vm_area_cachep, vma);
> >  }
> >
> > diff --git a/kernel/sys.c b/kernel/sys.c
> > index 72c7639e3c98..25118902a376 100644
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -2299,6 +2299,64 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struct *t, unsigned long which,
> >
> >  #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
> >
> > +#ifdef CONFIG_MMU
> > +
> > +#define ANON_VMA_NAME_MAX_LEN        256
> > +
> > +static inline bool is_valid_name_char(char ch)
> > +{
> > +     /* printable ascii characters, except [ \ ] */
> > +     return (ch > 0x1f && ch < 0x5b) || (ch > 0x5d && ch < 0x7f);
> > +}
> > +
> > +static int prctl_set_vma(unsigned long opt, unsigned long addr,
> > +                      unsigned long size, unsigned long arg)
> > +{
> > +     struct mm_struct *mm = current->mm;
> > +     const char __user *uname;
> > +     char *name, *pch;
> > +     int error;
> > +
> > +     switch (opt) {
> > +     case PR_SET_VMA_ANON_NAME:
> > +             uname = (const char __user *)arg;
> > +             if (!uname) {
> > +                     /* Reset the name */
> > +                     name = NULL;
> > +                     goto set_name;
> > +             }
> > +
> > +             name = strndup_user(uname, ANON_VMA_NAME_MAX_LEN);
> > +
> > +             if (IS_ERR(name))
> > +                     return PTR_ERR(name);
> > +
> > +             for (pch = name; *pch != '\0'; pch++) {
> > +                     if (!is_valid_name_char(*pch)) {
> > +                             kfree(name);
> > +                             return -EINVAL;
> > +                     }
> > +             }
> > +set_name:
> > +             mmap_write_lock(mm);
> > +             error = madvise_set_anon_name(mm, addr, size, name);
> > +             mmap_write_unlock(mm);
> > +             kfree(name);
> > +             break;
> > +     default:
> > +             error = -EINVAL;
> > +     }
> > +
> > +     return error;
> > +}
> > +#else /* CONFIG_MMU */
> > +static int prctl_set_vma(unsigned long opt, unsigned long start,
> > +                      unsigned long size, unsigned long arg)
> > +{
> > +     return -EINVAL;
> > +}
> > +#endif
> > +
> >  SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> >               unsigned long, arg4, unsigned long, arg5)
> >  {
> > @@ -2568,6 +2626,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> >               error = sched_core_share_pid(arg2, arg3, arg4, arg5);
> >               break;
> >  #endif
> > +     case PR_SET_VMA:
> > +             error = prctl_set_vma(arg2, arg3, arg4, arg5);
> > +             break;
> >       default:
> >               error = -EINVAL;
> >               break;
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 54bf9f73f95d..0c6d0f64d432 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/fadvise.h>
> >  #include <linux/sched.h>
> >  #include <linux/sched/mm.h>
> > +#include <linux/string.h>
> >  #include <linux/uio.h>
> >  #include <linux/ksm.h>
> >  #include <linux/fs.h>
> > @@ -62,19 +63,78 @@ static int madvise_need_mmap_write(int behavior)
> >       }
> >  }
> >
> > +static inline bool has_vma_anon_name(struct vm_area_struct *vma)
> > +{
> > +     return !vma->vm_file && vma->anon_name;
> > +}
> > +
> > +const char *vma_anon_name(struct vm_area_struct *vma)
> > +{
> > +     if (!has_vma_anon_name(vma))
> > +             return NULL;
> > +
> > +     mmap_assert_locked(vma->vm_mm);
> > +
> > +     return vma->anon_name;
> > +}
> > +
> > +void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> > +                    struct vm_area_struct *new_vma)
> > +{
> > +     if (!has_vma_anon_name(orig_vma))
> > +             return;
> > +
> > +     new_vma->anon_name = kstrdup(orig_vma->anon_name, GFP_KERNEL);
> > +}
> > +
> > +void free_vma_anon_name(struct vm_area_struct *vma)
> > +{
> > +     if (!has_vma_anon_name(vma))
> > +             return;
> > +
> > +     kfree(vma->anon_name);
> > +     vma->anon_name = NULL;
> > +}
> > +
> > +/* mmap_lock should be write-locked */
> > +static int replace_vma_anon_name(struct vm_area_struct *vma, const char *name)
> > +{
> > +     if (!name) {
> > +             free_vma_anon_name(vma);
> > +             return 0;
> > +     }
> > +
> > +     if (vma->anon_name) {
> > +             /* Should never happen, to dup use dup_vma_anon_name() */
> > +             WARN_ON(vma->anon_name == name);
> > +
> > +             /* Same name, nothing to do here */
> > +             if (!strcmp(name, vma->anon_name))
> > +                     return 0;
> > +
> > +             free_vma_anon_name(vma);
> > +     }
> > +     vma->anon_name = kstrdup(name, GFP_KERNEL);
> > +     if (!vma->anon_name)
> > +             return -ENOMEM;
> > +
> > +     return 0;
> > +}
> > +
> >  /*
> > - * Update the vm_flags on regiion of a vma, splitting it or merging it as
> > + * Update the vm_flags on region of a vma, splitting it or merging it as
> >   * necessary.  Must be called with mmap_sem held for writing;
> >   */
> >  static int madvise_update_vma(struct vm_area_struct *vma,
> >                             struct vm_area_struct **prev, unsigned long start,
> > -                           unsigned long end, unsigned long new_flags)
> > +                           unsigned long end, unsigned long new_flags,
> > +                           const char *name)
> >  {
> >       struct mm_struct *mm = vma->vm_mm;
> >       int error;
> >       pgoff_t pgoff;
> >
> > -     if (new_flags == vma->vm_flags) {
> > +     if (new_flags == vma->vm_flags && is_same_vma_anon_name(vma, name)) {
> >               *prev = vma;
> >               return 0;
> >       }
> > @@ -82,7 +142,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> >       pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> >       *prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
> >                         vma->vm_file, pgoff, vma_policy(vma),
> > -                       vma->vm_userfaultfd_ctx);
> > +                       vma->vm_userfaultfd_ctx, name);
> >       if (*prev) {
> >               vma = *prev;
> >               goto success;
> > @@ -91,20 +151,16 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> >       *prev = vma;
> >
> >       if (start != vma->vm_start) {
> > -             if (unlikely(mm->map_count >= sysctl_max_map_count)) {
> > -                     error = -ENOMEM;
> > -                     return error;
> > -             }
> > +             if (unlikely(mm->map_count >= sysctl_max_map_count))
> > +                     return -ENOMEM;
> >               error = __split_vma(mm, vma, start, 1);
> >               if (error)
> >                       return error;
> >       }
> >
> >       if (end != vma->vm_end) {
> > -             if (unlikely(mm->map_count >= sysctl_max_map_count)) {
> > -                     error = -ENOMEM;
> > -                     return error;
> > -             }
> > +             if (unlikely(mm->map_count >= sysctl_max_map_count))
> > +                     return -ENOMEM;
> >               error = __split_vma(mm, vma, end, 0);
> >               if (error)
> >                       return error;
> > @@ -115,10 +171,33 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> >        * vm_flags is protected by the mmap_lock held in write mode.
> >        */
> >       vma->vm_flags = new_flags;
> > +     if (!vma->vm_file) {
> > +             error = replace_vma_anon_name(vma, name);
> > +             if (error)
> > +                     return error;
> > +     }
> >
> >       return 0;
> >  }
> >
> > +static int madvise_vma_anon_name(struct vm_area_struct *vma,
> > +                              struct vm_area_struct **prev,
> > +                              unsigned long start, unsigned long end,
> > +                              unsigned long name)
> > +{
> > +     int error;
> > +
> > +     /* Only anonymous mappings can be named */
> > +     if (vma->vm_file)
> > +             return -EINVAL;
>
> To distinguish from the other EINVALs, should this maybe be EBADF? (As
> in "no, you can't do that, there is already an fd associated".)

Maybe. Although it's a bit strange to talk about a "bad file
descriptor" when the area is supposed to be anonymous. IMHO EINVAL is
the right answer here, but I might be convinced otherwise.

>
> > +
> > +     error = madvise_update_vma(vma, prev, start, end, vma->vm_flags,
> > +                                (const char *)name);
> > +     if (error == -ENOMEM)
> > +             error = -EAGAIN;
>
> I think a comment would be useful here too. AIUI, this is done to match
> the error behavior seen under madvise_vma_behavior().

Ack.

>
> > +     return error;
> > +}
> > +
> >  #ifdef CONFIG_SWAP
> >  static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
> >       unsigned long end, struct mm_walk *walk)
> > @@ -942,7 +1021,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
> >               break;
> >       }
> >
> > -     error = madvise_update_vma(vma, prev, start, end, new_flags);
> > +     error = madvise_update_vma(vma, prev, start, end, new_flags,
> > +                                vma_anon_name(vma));
> >
> >  out:
> >       /*
> > @@ -1121,6 +1201,31 @@ int madvise_walk_vmas(struct mm_struct *mm, unsigned long start,
> >       return unmapped_error;
> >  }
> >
> > +int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> > +                       unsigned long len_in, const char *name)
> > +{
> > +     unsigned long end;
> > +     unsigned long len;
> > +
> > +     if (start & ~PAGE_MASK)
> > +             return -EINVAL;
> > +     len = (len_in + ~PAGE_MASK) & PAGE_MASK;
> > +
> > +     /* Check to see whether len was rounded up from small -ve to zero */
> > +     if (len_in && !len)
> > +             return -EINVAL;
> > +
> > +     end = start + len;
> > +     if (end < start)
> > +             return -EINVAL;
> > +
> > +     if (end == start)
> > +             return 0;
> > +
> > +     return madvise_walk_vmas(mm, start, end, (unsigned long)name,
> > +                              madvise_vma_anon_name);
> > +}
> > +
> >  /*
> >   * The madvise(2) system call.
> >   *
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index e32360e90274..cc21ca7e9d40 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -811,7 +811,8 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
> >                       ((vmstart - vma->vm_start) >> PAGE_SHIFT);
> >               prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
> >                                vma->anon_vma, vma->vm_file, pgoff,
> > -                              new_pol, vma->vm_userfaultfd_ctx);
> > +                              new_pol, vma->vm_userfaultfd_ctx,
> > +                              vma_anon_name(vma));
> >               if (prev) {
> >                       vma = prev;
> >                       next = vma->vm_next;
> > diff --git a/mm/mlock.c b/mm/mlock.c
> > index 16d2ee160d43..c878515680af 100644
> > --- a/mm/mlock.c
> > +++ b/mm/mlock.c
> > @@ -511,7 +511,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
> >       pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> >       *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
> >                         vma->vm_file, pgoff, vma_policy(vma),
> > -                       vma->vm_userfaultfd_ctx);
> > +                       vma->vm_userfaultfd_ctx, vma_anon_name(vma));
> >       if (*prev) {
> >               vma = *prev;
> >               goto success;
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 181a113b545d..c13934d41f65 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -1032,7 +1032,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
> >   */
> >  static inline int is_mergeable_vma(struct vm_area_struct *vma,
> >                               struct file *file, unsigned long vm_flags,
> > -                             struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> > +                             struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> > +                             const char *anon_name)
> >  {
> >       /*
> >        * VM_SOFTDIRTY should not prevent from VMA merging, if we
> > @@ -1050,6 +1051,8 @@ static inline int is_mergeable_vma(struct vm_area_struct *vma,
> >               return 0;
> >       if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
> >               return 0;
> > +     if (!is_same_vma_anon_name(vma, anon_name))
> > +             return 0;
> >       return 1;
> >  }
> >
> > @@ -1082,9 +1085,10 @@ static int
> >  can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
> >                    struct anon_vma *anon_vma, struct file *file,
> >                    pgoff_t vm_pgoff,
> > -                  struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> > +                  struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> > +                  const char *anon_name)
> >  {
> > -     if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
> > +     if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
> >           is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
> >               if (vma->vm_pgoff == vm_pgoff)
> >                       return 1;
> > @@ -1103,9 +1107,10 @@ static int
> >  can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
> >                   struct anon_vma *anon_vma, struct file *file,
> >                   pgoff_t vm_pgoff,
> > -                 struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> > +                 struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> > +                  const char *anon_name)
>
> Nit: one too many spaces before "const".

Ack.

>
> >  {
> > -     if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
> > +     if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
> >           is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
> >               pgoff_t vm_pglen;
> >               vm_pglen = vma_pages(vma);
> > @@ -1116,9 +1121,9 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
> >  }
> >
> >  /*
> > - * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
> > - * whether that can be merged with its predecessor or its successor.
> > - * Or both (it neatly fills a hole).
> > + * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
> > + * figure out whether that can be merged with its predecessor or its
> > + * successor.  Or both (it neatly fills a hole).
> >   *
> >   * In most cases - when called for mmap, brk or mremap - [addr,end) is
> >   * certain not to be mapped by the time vma_merge is called; but when
> > @@ -1163,7 +1168,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
> >                       unsigned long end, unsigned long vm_flags,
> >                       struct anon_vma *anon_vma, struct file *file,
> >                       pgoff_t pgoff, struct mempolicy *policy,
> > -                     struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> > +                     struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> > +                     const char *anon_name)
> >  {
> >       pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
> >       struct vm_area_struct *area, *next;
> > @@ -1193,7 +1199,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
> >                       mpol_equal(vma_policy(prev), policy) &&
> >                       can_vma_merge_after(prev, vm_flags,
> >                                           anon_vma, file, pgoff,
> > -                                         vm_userfaultfd_ctx)) {
> > +                                         vm_userfaultfd_ctx, anon_name)) {
> >               /*
> >                * OK, it can.  Can we now merge in the successor as well?
> >                */
> > @@ -1202,7 +1208,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
> >                               can_vma_merge_before(next, vm_flags,
> >                                                    anon_vma, file,
> >                                                    pgoff+pglen,
> > -                                                  vm_userfaultfd_ctx) &&
> > +                                                  vm_userfaultfd_ctx, anon_name) &&
> >                               is_mergeable_anon_vma(prev->anon_vma,
> >                                                     next->anon_vma, NULL)) {
> >                                                       /* cases 1, 6 */
> > @@ -1225,7 +1231,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
> >                       mpol_equal(policy, vma_policy(next)) &&
> >                       can_vma_merge_before(next, vm_flags,
> >                                            anon_vma, file, pgoff+pglen,
> > -                                          vm_userfaultfd_ctx)) {
> > +                                          vm_userfaultfd_ctx, anon_name)) {
> >               if (prev && addr < prev->vm_end)        /* case 4 */
> >                       err = __vma_adjust(prev, prev->vm_start,
> >                                        addr, prev->vm_pgoff, NULL, next);
> > @@ -1760,7 +1766,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >        * Can we just expand an old mapping?
> >        */
> >       vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
> > -                     NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX);
> > +                     NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
> >       if (vma)
> >               goto out;
> >
> > @@ -1819,7 +1825,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >                */
> >               if (unlikely(vm_flags != vma->vm_flags && prev)) {
> >                       merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
> > -                             NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
> > +                             NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
> >                       if (merge) {
> >                               /* ->mmap() can change vma->vm_file and fput the original file. So
> >                                * fput the vma->vm_file here or we would add an extra fput for file
> > @@ -3081,7 +3087,7 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
> >
> >       /* Can we just expand an old private anonymous mapping? */
> >       vma = vma_merge(mm, prev, addr, addr + len, flags,
> > -                     NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX);
> > +                     NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
> >       if (vma)
> >               goto out;
> >
> > @@ -3274,7 +3280,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
> >               return NULL;    /* should never get here */
> >       new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
> >                           vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
> > -                         vma->vm_userfaultfd_ctx);
> > +                         vma->vm_userfaultfd_ctx, vma_anon_name(vma));
> >       if (new_vma) {
> >               /*
> >                * Source vma may have been merged into new_vma
> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index 883e2cc85cad..a48ff8e79f48 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -464,7 +464,7 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
> >       pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> >       *pprev = vma_merge(mm, *pprev, start, end, newflags,
> >                          vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
> > -                        vma->vm_userfaultfd_ctx);
> > +                        vma->vm_userfaultfd_ctx, vma_anon_name(vma));
> >       if (*pprev) {
> >               vma = *pprev;
> >               VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
> > --
> > 2.33.0.153.gba50c8fa24-goog
> >
>
> Cool. With my notes above addressed, please consider this:
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
>

Thanks! Will copy it into the next rev with fixes.
Suren.

> --
> Kees Cook