hostmem-file: reject invalid pmem file sizes

Message ID 20190212025241.5330-1-stefanha@redhat.com
State New
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Series
  • hostmem-file: reject invalid pmem file sizes
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Commit Message

Stefan Hajnoczi Feb. 12, 2019, 2:52 a.m.
Guests started with NVDIMMs larger than the underlying host file produce
confusing errors inside the guest.  This happens because the guest
accesses pages beyond the end of the file.

Check the pmem file size on startup and print a clear error message if
the size is invalid.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1669053
Cc: Haozhong Zhang <haozhong.zhang@intel.com>
Cc: Zhang Yi <yi.z.zhang@linux.intel.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/qemu/osdep.h    | 13 ++++++++++
 backends/hostmem-file.c | 16 +++++++++++++
 util/oslib-posix.c      | 53 +++++++++++++++++++++++++++++++++++++++++
 util/oslib-win32.c      |  5 ++++
 4 files changed, 87 insertions(+)

Comments

Pankaj Gupta Feb. 12, 2019, 8:57 a.m. | #1
Hi Stefan,

> 
> Guests started with NVDIMMs larger than the underlying host file produce
> confusing errors inside the guest.  This happens because the guest
> accesses pages beyond the end of the file.
> 
> Check the pmem file size on startup and print a clear error message if
> the size is invalid.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1669053
> Cc: Haozhong Zhang <haozhong.zhang@intel.com>
> Cc: Zhang Yi <yi.z.zhang@linux.intel.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/qemu/osdep.h    | 13 ++++++++++
>  backends/hostmem-file.c | 16 +++++++++++++
>  util/oslib-posix.c      | 53 +++++++++++++++++++++++++++++++++++++++++
>  util/oslib-win32.c      |  5 ++++
>  4 files changed, 87 insertions(+)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 840af09cb0..303d315c5d 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -570,6 +570,19 @@ void qemu_set_tty_echo(int fd, bool echo);
>  void os_mem_prealloc(int fd, char *area, size_t sz, int smp_cpus,
>                       Error **errp);
>  
> +/**
> + * qemu_get_pmem_size:
> + * @filename: path to a pmem file
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Determine the size of a persistent memory file.  Besides supporting files
> on
> + * DAX file systems, this function also supports Linux devdax character
> + * devices.
> + *
> + * Returns: the size or 0 on failure
> + */
> +uint64_t qemu_get_pmem_size(const char *filename, Error **errp);
> +
>  /**
>   * qemu_get_pid_name:
>   * @pid: pid of a process
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index ba601ce940..325ab4aad9 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -46,6 +46,22 @@ file_backend_memory_alloc(HostMemoryBackend *backend,
> Error **errp)
>      gchar *name;
>  #endif
>  
> +    /*
> +     * Verify pmem file size since starting a guest with an incorrect size
> +     * leads to confusing failures inside the guest.
> +     */
> +    if (fb->is_pmem && fb->mem_path) {
> +        uint64_t size;
> +
> +        size = qemu_get_pmem_size(fb->mem_path, NULL);
> +        if (size && backend->size > size) {
> +            error_setg(errp, "size property %" PRIu64 " is larger than "
> +                       "pmem file \"%s\" size %" PRIu64, backend->size,
> +                       fb->mem_path, size);
> +            return;
> +        }
> +    }
> +
>      if (!backend->size) {
>          error_setg(errp, "can't create backend with size 0");
>          return;
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 37c5854b9c..10d90d1783 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -500,6 +500,59 @@ void os_mem_prealloc(int fd, char *area, size_t memory,
> int smp_cpus,
>      }
>  }
>  
> +uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
> +{
> +    struct stat st;
> +
> +    if (stat(filename, &st) < 0) {
> +        error_setg(errp, "unable to stat pmem file \"%s\"", filename);
> +        return 0;
> +    }
> +
> +#if defined(__linux__)
> +    /* Special handling for devdax character devices */
> +    if (S_ISCHR(st.st_mode)) {
> +        char *subsystem_path = NULL;
> +        char *subsystem = NULL;
> +        char *size_path = NULL;
> +        char *size_str = NULL;
> +        uint64_t ret = 0;
> +
> +        subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",
> +                                         major(st.st_rdev),
> minor(st.st_rdev));
> +        subsystem = g_file_read_link(subsystem_path, NULL);
> +        if (!subsystem) {
> +            error_setg(errp, "unable to read subsystem for pmem file
> \"%s\"",
> +                       filename);
> +            goto devdax_err;
> +        }
> +
> +        if (!g_str_has_suffix(subsystem, "/dax")) {
> +            error_setg(errp, "pmem file \"%s\" is not a dax device",
> filename);
> +            goto devdax_err;
> +        }
> +
> +        size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",
> +                                    major(st.st_rdev), minor(st.st_rdev));
> +        if (!g_file_get_contents(size_path, &size_str, NULL, NULL)) {
> +            error_setg(errp, "unable to read size for pmem file \"%s\"",
> +                       size_path);
> +            goto devdax_err;
> +        }
> +
> +        ret = g_ascii_strtoull(size_str, NULL, 0);
> +
> +devdax_err:
> +        g_free(size_str);
> +        g_free(size_path);
> +        g_free(subsystem);
> +        g_free(subsystem_path);
> +        return ret;
> +    }
> +#endif /* defined(__linux__) */
> +
> +    return st.st_size;
> +}
>  
>  char *qemu_get_pid_name(pid_t pid)
>  {
> diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> index b4c17f5dfa..bd633afab6 100644
> --- a/util/oslib-win32.c
> +++ b/util/oslib-win32.c
> @@ -560,6 +560,11 @@ void os_mem_prealloc(int fd, char *area, size_t memory,
> int smp_cpus,
>      }
>  }
>  
> +uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
> +{
> +    error_setg(errp, "pmem support not available");
> +    return 0;
> +}
>  
>  char *qemu_get_pid_name(pid_t pid)
>  {
> --
> 2.20.1

This patch looks good to me.

Reviewed-by: Pankaj Gupta <pagupta@redhat.com>

Thanks,
Pankaj
Igor Mammedov Feb. 12, 2019, 2:44 p.m. | #2
On Tue, 12 Feb 2019 10:52:41 +0800
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> Guests started with NVDIMMs larger than the underlying host file produce
> confusing errors inside the guest.  This happens because the guest
> accesses pages beyond the end of the file.
> 
> Check the pmem file size on startup and print a clear error message if
> the size is invalid.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1669053
> Cc: Haozhong Zhang <haozhong.zhang@intel.com>
> Cc: Zhang Yi <yi.z.zhang@linux.intel.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/qemu/osdep.h    | 13 ++++++++++
>  backends/hostmem-file.c | 16 +++++++++++++
>  util/oslib-posix.c      | 53 +++++++++++++++++++++++++++++++++++++++++
>  util/oslib-win32.c      |  5 ++++
>  4 files changed, 87 insertions(+)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 840af09cb0..303d315c5d 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -570,6 +570,19 @@ void qemu_set_tty_echo(int fd, bool echo);
>  void os_mem_prealloc(int fd, char *area, size_t sz, int smp_cpus,
>                       Error **errp);
>  
> +/**
> + * qemu_get_pmem_size:
> + * @filename: path to a pmem file
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Determine the size of a persistent memory file.  Besides supporting files on
> + * DAX file systems, this function also supports Linux devdax character
> + * devices.
> + *
> + * Returns: the size or 0 on failure
> + */
> +uint64_t qemu_get_pmem_size(const char *filename, Error **errp);
> +
>  /**
>   * qemu_get_pid_name:
>   * @pid: pid of a process
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index ba601ce940..325ab4aad9 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -46,6 +46,22 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
>      gchar *name;
>  #endif
>  
> +    /*
> +     * Verify pmem file size since starting a guest with an incorrect size
> +     * leads to confusing failures inside the guest.
> +     */
> +    if (fb->is_pmem && fb->mem_path) {
> +        uint64_t size;
> +
> +        size = qemu_get_pmem_size(fb->mem_path, NULL);
                                                   ^^^^
Did you ignore error intentionally?

> +        if (size && backend->size > size) {
> +            error_setg(errp, "size property %" PRIu64 " is larger than "
> +                       "pmem file \"%s\" size %" PRIu64, backend->size,
> +                       fb->mem_path, size);
> +            return;
> +        }
> +    }
> +
>      if (!backend->size) {
>          error_setg(errp, "can't create backend with size 0");
>          return;
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 37c5854b9c..10d90d1783 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -500,6 +500,59 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
>      }
>  }
>  
> +uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
> +{
> +    struct stat st;
> +
> +    if (stat(filename, &st) < 0) {
> +        error_setg(errp, "unable to stat pmem file \"%s\"", filename);
> +        return 0;
> +    }
> +
> +#if defined(__linux__)
> +    /* Special handling for devdax character devices */
> +    if (S_ISCHR(st.st_mode)) {
> +        char *subsystem_path = NULL;
> +        char *subsystem = NULL;
> +        char *size_path = NULL;
> +        char *size_str = NULL;
> +        uint64_t ret = 0;
> +
> +        subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",
> +                                         major(st.st_rdev), minor(st.st_rdev));
> +        subsystem = g_file_read_link(subsystem_path, NULL);
> +        if (!subsystem) {
> +            error_setg(errp, "unable to read subsystem for pmem file \"%s\"",
> +                       filename);
> +            goto devdax_err;
> +        }
> +
> +        if (!g_str_has_suffix(subsystem, "/dax")) {
> +            error_setg(errp, "pmem file \"%s\" is not a dax device", filename);
> +            goto devdax_err;
> +        }
> +
> +        size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",
> +                                    major(st.st_rdev), minor(st.st_rdev));
> +        if (!g_file_get_contents(size_path, &size_str, NULL, NULL)) {
> +            error_setg(errp, "unable to read size for pmem file \"%s\"",
> +                       size_path);
> +            goto devdax_err;
> +        }
> +
> +        ret = g_ascii_strtoull(size_str, NULL, 0);
> +
> +devdax_err:
> +        g_free(size_str);
> +        g_free(size_path);
> +        g_free(subsystem);
> +        g_free(subsystem_path);
> +        return ret;
> +    }
> +#endif /* defined(__linux__) */
> +
> +    return st.st_size;
> +}
>  
>  char *qemu_get_pid_name(pid_t pid)
>  {
> diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> index b4c17f5dfa..bd633afab6 100644
> --- a/util/oslib-win32.c
> +++ b/util/oslib-win32.c
> @@ -560,6 +560,11 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
>      }
>  }
>  
> +uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
> +{
> +    error_setg(errp, "pmem support not available");
> +    return 0;
> +}
>  
>  char *qemu_get_pid_name(pid_t pid)
>  {
Stefan Hajnoczi Feb. 13, 2019, 7:01 a.m. | #3
On Tue, Feb 12, 2019 at 03:44:46PM +0100, Igor Mammedov wrote:
> > diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> > index ba601ce940..325ab4aad9 100644
> > --- a/backends/hostmem-file.c
> > +++ b/backends/hostmem-file.c
> > @@ -46,6 +46,22 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
> >      gchar *name;
> >  #endif
> >  
> > +    /*
> > +     * Verify pmem file size since starting a guest with an incorrect size
> > +     * leads to confusing failures inside the guest.
> > +     */
> > +    if (fb->is_pmem && fb->mem_path) {
> > +        uint64_t size;
> > +
> > +        size = qemu_get_pmem_size(fb->mem_path, NULL);
>                                                    ^^^^
> Did you ignore error intentionally?

Hmm...I think I can now propagate the error.  Originally the function
only handled devdax chardevs so it would fail for a regular file on a
DAX file system and that shouldn't stop QEMU startup.  But now that it
supports regular files too I can't think of inputs that lead to a false
positive.

Will fix in v2.

Stefan

Patch

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 840af09cb0..303d315c5d 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -570,6 +570,19 @@  void qemu_set_tty_echo(int fd, bool echo);
 void os_mem_prealloc(int fd, char *area, size_t sz, int smp_cpus,
                      Error **errp);
 
+/**
+ * qemu_get_pmem_size:
+ * @filename: path to a pmem file
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Determine the size of a persistent memory file.  Besides supporting files on
+ * DAX file systems, this function also supports Linux devdax character
+ * devices.
+ *
+ * Returns: the size or 0 on failure
+ */
+uint64_t qemu_get_pmem_size(const char *filename, Error **errp);
+
 /**
  * qemu_get_pid_name:
  * @pid: pid of a process
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index ba601ce940..325ab4aad9 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -46,6 +46,22 @@  file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     gchar *name;
 #endif
 
+    /*
+     * Verify pmem file size since starting a guest with an incorrect size
+     * leads to confusing failures inside the guest.
+     */
+    if (fb->is_pmem && fb->mem_path) {
+        uint64_t size;
+
+        size = qemu_get_pmem_size(fb->mem_path, NULL);
+        if (size && backend->size > size) {
+            error_setg(errp, "size property %" PRIu64 " is larger than "
+                       "pmem file \"%s\" size %" PRIu64, backend->size,
+                       fb->mem_path, size);
+            return;
+        }
+    }
+
     if (!backend->size) {
         error_setg(errp, "can't create backend with size 0");
         return;
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 37c5854b9c..10d90d1783 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -500,6 +500,59 @@  void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
     }
 }
 
+uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
+{
+    struct stat st;
+
+    if (stat(filename, &st) < 0) {
+        error_setg(errp, "unable to stat pmem file \"%s\"", filename);
+        return 0;
+    }
+
+#if defined(__linux__)
+    /* Special handling for devdax character devices */
+    if (S_ISCHR(st.st_mode)) {
+        char *subsystem_path = NULL;
+        char *subsystem = NULL;
+        char *size_path = NULL;
+        char *size_str = NULL;
+        uint64_t ret = 0;
+
+        subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",
+                                         major(st.st_rdev), minor(st.st_rdev));
+        subsystem = g_file_read_link(subsystem_path, NULL);
+        if (!subsystem) {
+            error_setg(errp, "unable to read subsystem for pmem file \"%s\"",
+                       filename);
+            goto devdax_err;
+        }
+
+        if (!g_str_has_suffix(subsystem, "/dax")) {
+            error_setg(errp, "pmem file \"%s\" is not a dax device", filename);
+            goto devdax_err;
+        }
+
+        size_path = g_strdup_printf("/sys/dev/char/%d:%d/size",
+                                    major(st.st_rdev), minor(st.st_rdev));
+        if (!g_file_get_contents(size_path, &size_str, NULL, NULL)) {
+            error_setg(errp, "unable to read size for pmem file \"%s\"",
+                       size_path);
+            goto devdax_err;
+        }
+
+        ret = g_ascii_strtoull(size_str, NULL, 0);
+
+devdax_err:
+        g_free(size_str);
+        g_free(size_path);
+        g_free(subsystem);
+        g_free(subsystem_path);
+        return ret;
+    }
+#endif /* defined(__linux__) */
+
+    return st.st_size;
+}
 
 char *qemu_get_pid_name(pid_t pid)
 {
diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index b4c17f5dfa..bd633afab6 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -560,6 +560,11 @@  void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
     }
 }
 
+uint64_t qemu_get_pmem_size(const char *filename, Error **errp)
+{
+    error_setg(errp, "pmem support not available");
+    return 0;
+}
 
 char *qemu_get_pid_name(pid_t pid)
 {