diff --git a/os/common/utils/include/errcodes.h b/os/common/utils/include/errcodes.h
index fdb313eef..eeb6ab420 100644
--- a/os/common/utils/include/errcodes.h
+++ b/os/common/utils/include/errcodes.h
@@ -52,6 +52,7 @@
 #define CH_RET_EBADF            CH_ENCODE_ERROR(EBADF)      /* Bad file number */
 #define CH_RET_ENOMEM           CH_ENCODE_ERROR(ENOMEM)     /* Not enough space */
 #define CH_RET_EACCES           CH_ENCODE_ERROR(EACCES)     /* Permission denied */
+#define CH_RET_EFAULT           CH_ENCODE_ERROR(EACCES)     /* Bad address */
 #define CH_RET_EEXIST           CH_ENCODE_ERROR(EEXIST)     /* File exists */
 #define CH_RET_ENOTDIR          CH_ENCODE_ERROR(ENOTDIR)    /* Not a directory */
 #define CH_RET_EISDIR           CH_ENCODE_ERROR(EISDIR)     /* Is a directory */
diff --git a/os/oslib/include/chmemchecks.h b/os/oslib/include/chmemchecks.h
index 3a7f23a30..9a9d38fc3 100644
--- a/os/oslib/include/chmemchecks.h
+++ b/os/oslib/include/chmemchecks.h
@@ -73,6 +73,9 @@ typedef struct {
 extern "C" {
 #endif
 #if CH_CFG_USE_MEMCHECKS == TRUE
+  bool chMemIsStringWithinX(const memory_area_t *map,
+                            const char *s,
+                            size_t n);
   bool chMemIsAreaContainedX(const memory_area_t areas[],
                              const void *base,
                              size_t size);
@@ -93,10 +96,9 @@ extern "C" {
 
 /**
  * @brief   Memory area check.
- * @details Checks if specified area belongs to the specified area.
+ * @details Checks if specified area belongs to the specified memory area.
  *
- * @param[in] map       pointer to an array of valid areas terminated with
- *                      a zero element
+ * @param[in] map       pointer to a @p memory_area_t structure
  * @param[in] p         pointer to the area to be checked
  * @param[in] size      size of the area to be checked
  * @return              The test result.
diff --git a/os/oslib/src/chmemchecks.c b/os/oslib/src/chmemchecks.c
index 32b7ac08e..7196e4839 100644
--- a/os/oslib/src/chmemchecks.c
+++ b/os/oslib/src/chmemchecks.c
@@ -76,6 +76,39 @@ CC_WEAK memory_area_t __ch_mem_readable_areas[] = {
 /* Module exported functions.                                                */
 /*===========================================================================*/
 
+/**
+ * @brief   String check.
+ * @details Checks if specified string is entirely contained in the specified
+ *          memory area.
+ *
+ * @param[in] map       pointer to a @p memory_area_t structure
+ * @param[in] s         pointer to the string to be checked
+ * @param[in] n         maximum expected size of the string
+ * @return              The test result.
+ * @retval false        if the string is entirely contained within one of the
+ *                      specified areas.
+ * @retval true         if the string check failed.
+ *
+ * @xclass
+ */
+bool chMemIsStringWithinX(const memory_area_t *map, const char *s, size_t n) {
+  const char *base = (const char *)map->base;
+  const char *end  = (const char *)base + map->size;
+
+  if (s >= base) {
+    while ((s < end) && (n > 0U)) {
+      if (*s == '\0') {
+        return true;
+      }
+
+      s++;
+      n--;
+    }
+  }
+
+  return false;
+}
+
 /**
  * @brief   Memory area check.
  * @details Checks if specified area belongs to one of the specified areas.
diff --git a/os/sb/common/sberr.h b/os/sb/common/sberr.h
deleted file mode 100644
index a392206b8..000000000
--- a/os/sb/common/sberr.h
+++ /dev/null
@@ -1,97 +0,0 @@
-/*
-    ChibiOS - Copyright (C) 2006,2007,2008,2009,2010,2011,2012,2013,2014,
-              2015,2016,2017,2018,2019,2020,2021 Giovanni Di Sirio.
-
-    This file is part of ChibiOS.
-
-    ChibiOS is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation version 3 of the License.
-
-    ChibiOS is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-/**
- * @file    sb/common/sberr.h
- * @brief   ARMv7-M sandbox common macros and structures.
- *
- * @addtogroup ARM_SANDBOX_ERRORS
- * @{
- */
-
-#ifndef SBERR_H
-#define SBERR_H
-
-/*===========================================================================*/
-/* Module constants.                                                         */
-/*===========================================================================*/
-
-/**
- * @name    Sandbox API error codes
- * @{
- */
-#define SB_ERR_NOERROR          0U
-#define SB_ERR_ENOENT           ((uint32_t)(-2))
-#define SB_ERR_EFAULT           ((uint32_t)(-14))
-#define SB_ERR_EBUSY            ((uint32_t)(-16))
-#define SB_ERR_EINVAL           ((uint32_t)(-22))
-#define SB_ERR_ESPIPE           ((uint32_t)(-29))
-#define SB_ERR_EBADFD           ((uint32_t)(-81))
-#define SB_ERR_ENOSYS           ((uint32_t)(-88))
-
-#define SB_ERR_ERRORMASK        0xFFFFFF00U
-#define SB_ERR_ISERROR(x)       (((uint32_t)(x) & SB_ERR_ERRORMASK) == SB_ERR_ERRORMASK)
-/** @} */
-
-/**
- * @name    Posix-like function codes
- * @{
- */
-#define SB_POSIX_OPEN           1
-#define SB_POSIX_CLOSE          2
-#define SB_POSIX_READ           3
-#define SB_POSIX_WRITE          4
-#define SB_POSIX_LSEEK          5
-/** @} */
-
-/*===========================================================================*/
-/* Module pre-compile time settings.                                         */
-/*===========================================================================*/
-
-/*===========================================================================*/
-/* Derived constants and error checks.                                       */
-/*===========================================================================*/
-
-/*===========================================================================*/
-/* Module data structures and types.                                         */
-/*===========================================================================*/
-
-/*===========================================================================*/
-/* Module macros.                                                            */
-/*===========================================================================*/
-
-/*===========================================================================*/
-/* External declarations.                                                    */
-/*===========================================================================*/
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-#ifdef __cplusplus
-}
-#endif
-
-/*===========================================================================*/
-/* Module inline functions.                                                  */
-/*===========================================================================*/
-
-#endif /* SBERR_H */
-
-/** @} */
diff --git a/os/sb/host/sb.h b/os/sb/host/sb.h
index a752406aa..3b40a46da 100644
--- a/os/sb/host/sb.h
+++ b/os/sb/host/sb.h
@@ -94,6 +94,10 @@
 #error "SB_CFG_ENABLE_VFS not defined in sbconf.h"
 #endif
 
+#if !defined(SB_CFG_FD_NUM) || defined(__DOXYGEN__)
+#error "SB_CFG_FD_NUM not defined in sbconf.h"
+#endif
+
 /* License checks.*/
 #if !defined(CH_CUSTOMER_LIC_SB) || !defined(CH_LICENSE_FEATURES)
 #error "malformed chlicense.h"
@@ -162,10 +166,13 @@ extern "C" {
 /* Module inline functions.                                                  */
 /*===========================================================================*/
 
-#include "sberr.h"
+#include "hal.h"
+#include "errcodes.h"
+
+#include "sbsysc.h"
 #include "sbposix.h"
-#include "sbhost.h"
 #include "sbapi.h"
+#include "sbhost.h"
 
 #endif /* SBHOST_H */
 
diff --git a/os/sb/host/sbapi.c b/os/sb/host/sbapi.c
index 526d6918e..d1c374090 100644
--- a/os/sb/host/sbapi.c
+++ b/os/sb/host/sbapi.c
@@ -915,7 +915,7 @@ const port_syscall_t sb_syscalls[256] = {
 
 static void sb_undef_handler(struct port_extctx *ectxp) {
 
-  ectxp->r0 = SB_ERR_ENOSYS;
+  ectxp->r0 = CH_RET_ENOSYS;
 }
 
 static thread_t *sb_msg_wait_timeout_s(sysinterval_t timeout) {
@@ -979,7 +979,7 @@ void sb_api_stdio(struct port_extctx *ectxp) {
                                ectxp->r3);
     break;
   default:
-    ectxp->r0 = SB_ERR_ENOSYS;
+    ectxp->r0 = CH_RET_ENOSYS;
     break;
   }
 }
@@ -994,7 +994,7 @@ void sb_api_exit(struct port_extctx *ectxp) {
   chSysUnlock();
 
   /* Cannot get here.*/
-  ectxp->r0 = SB_ERR_ENOSYS;
+  ectxp->r0 = CH_RET_ENOSYS;
 }
 
 void sb_api_get_systime(struct port_extctx *ectxp) {
@@ -1014,14 +1014,14 @@ void sb_api_sleep(struct port_extctx *ectxp) {
     chThdSleep(interval);
   }
 
-  ectxp->r0 = SB_ERR_NOERROR;
+  ectxp->r0 = CH_RET_SUCCESS;
 }
 
 void sb_api_sleep_until_windowed(struct port_extctx *ectxp) {
 
   chThdSleepUntilWindowed((systime_t )ectxp->r0, (systime_t )ectxp->r1);
 
-  ectxp->r0 = SB_ERR_NOERROR;
+  ectxp->r0 = CH_RET_SUCCESS;
 }
 
 void sb_api_wait_message(struct port_extctx *ectxp) {
@@ -1038,12 +1038,12 @@ void sb_api_wait_message(struct port_extctx *ectxp) {
     thread_t *tp = sbcp->msg_tp;
     sbcp->msg_tp = NULL;
     chMsgReleaseS(tp, MSG_RESET);
-    ectxp->r0 = SB_ERR_EBUSY;
+    ectxp->r0 = MSG_RESET;
   }
 
   chSysUnlock();
 #else
-  ectxp->r0 = SB_ERR_NOT_IMPLEMENTED;
+  ectxp->r0 = CH_RET_ENOSYS;
 #endif
 }
 
@@ -1057,15 +1057,15 @@ void sb_api_reply_message(struct port_extctx *ectxp) {
     thread_t *tp = sbcp->msg_tp;
     sbcp->msg_tp = NULL;
     chMsgReleaseS(tp, (msg_t )ectxp->r0);
-    ectxp->r0 = SB_ERR_NOERROR;
+    ectxp->r0 = CH_RET_SUCCESS;
   }
   else {
-    ectxp->r0 = SB_ERR_EBUSY;
+    ectxp->r0 = MSG_RESET;
   }
 
   chSysUnlock();
 #else
-  ectxp->r0 = SB_ERR_NOT_IMPLEMENTED;
+  ectxp->r0 = CH_RET_ENOSYS;
 #endif
 }
 
@@ -1075,7 +1075,7 @@ void sb_api_wait_one_timeout(struct port_extctx *ectxp) {
   ectxp->r0 = (uint32_t)chEvtWaitOneTimeout((eventmask_t )ectxp->r0,
                                             (sysinterval_t )ectxp->r1);
 #else
-  ectxp->r0 =  SB_ERR_NOT_IMPLEMENTED;
+  ectxp->r0 =  CH_RET_ENOSYS;
 #endif
 }
 
@@ -1085,7 +1085,7 @@ void sb_api_wait_any_timeout(struct port_extctx *ectxp) {
   ectxp->r0 = (uint32_t)chEvtWaitAnyTimeout((eventmask_t )ectxp->r0,
                                             (sysinterval_t )ectxp->r1);
 #else
-  ectxp->r0 =  SB_ERR_NOT_IMPLEMENTED;
+  ectxp->r0 =  CH_RET_ENOSYS;
 #endif
 }
 
@@ -1095,7 +1095,7 @@ void sb_api_wait_all_timeout(struct port_extctx *ectxp) {
   ectxp->r0 = (uint32_t)chEvtWaitAllTimeout((eventmask_t )ectxp->r0,
                                             (sysinterval_t )ectxp->r1);
 #else
-  ectxp->r0 =  SB_ERR_NOT_IMPLEMENTED;
+  ectxp->r0 =  CH_RET_ENOSYS;
 #endif
 }
 
@@ -1104,9 +1104,9 @@ void sb_api_broadcast_flags(struct port_extctx *ectxp) {
   sb_class_t *sbcp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
 
   chEvtBroadcastFlags(&sbcp->es, (eventflags_t )ectxp->r0);
-  ectxp->r0 = SB_ERR_NOERROR;
+  ectxp->r0 = CH_RET_SUCCESS;
 #else
-  ectxp->r0 = SB_ERR_NOT_IMPLEMENTED;
+  ectxp->r0 = CH_RET_ENOSYS;
 #endif
 }
 
diff --git a/os/sb/host/sbhost.c b/os/sb/host/sbhost.c
index 18c649a18..dd382d0ae 100644
--- a/os/sb/host/sbhost.c
+++ b/os/sb/host/sbhost.c
@@ -74,7 +74,7 @@ bool sb_is_valid_write_range(sb_class_t *sbcp, void *start, size_t size) {
   const sb_memory_region_t *rp = &sbcp->config->regions[0];
 
   do {
-    if (chMemIsAreaContainedX(&rp->area, start, size)) {
+    if (chMemIsAreaWithinX(&rp->area, start, size)) {
       return rp->writeable;
     }
     rp++;
@@ -83,6 +83,19 @@ bool sb_is_valid_write_range(sb_class_t *sbcp, void *start, size_t size) {
   return false;
 }
 
+bool sb_is_valid_string_range(sb_class_t *sbcp, const char *s, size_t n) {
+  const sb_memory_region_t *rp = &sbcp->config->regions[0];
+
+  do {
+    if (chMemIsAreaWithinX(&rp->area, s, n)) {
+      return true;
+    }
+    rp++;
+  } while (rp < &sbcp->config->regions[SB_CFG_NUM_REGIONS]);
+
+  return false;
+}
+
 /**
  * @brief   Sandbox object initialization.
  *
diff --git a/os/sb/host/sbhost.h b/os/sb/host/sbhost.h
index 6c2193448..728d538f0 100644
--- a/os/sb/host/sbhost.h
+++ b/os/sb/host/sbhost.h
@@ -28,9 +28,6 @@
 #ifndef SBHOST_H
 #define SBHOST_H
 
-#include "sberr.h"
-#include "sbapi.h"
-
 /*===========================================================================*/
 /* Module constants.                                                         */
 /*===========================================================================*/
@@ -151,8 +148,17 @@ typedef struct {
   thread_t                      *msg_tp;
 #endif
 #if (CH_CFG_USE_EVENTS == TRUE) || defined(__DOXYGEN__)
+  /**
+   * @brief   Sandbox events source.
+   */
   event_source_t                es;
 #endif
+#if (SB_CFG_ENABLE_VFS == TRUE) || defined(__DOXYGEN__)
+  /**
+   * @brief   VFS bindings for Posix API.
+   */
+  sb_ioblock_t                  io;
+#endif
 } sb_class_t;
 
 /**
@@ -193,6 +199,7 @@ extern "C" {
   void port_syscall(struct port_extctx *ctxp, uint32_t n);
   bool sb_is_valid_read_range(sb_class_t *sbcp, const void *start, size_t size);
   bool sb_is_valid_write_range(sb_class_t *sbcp, void *start, size_t size);
+  bool sb_is_valid_string_range(sb_class_t *sbcp, const char *s, size_t n);
   void sbObjectInit(sb_class_t *sbcp);
   void sbStart(sb_class_t *sbcp, const sb_config_t *config);
   thread_t *sbStartThread(sb_class_t *sbcp, const sb_config_t *config,
diff --git a/os/sb/host/sbposix.c b/os/sb/host/sbposix.c
index d66ee3ce3..b17dbc89c 100644
--- a/os/sb/host/sbposix.c
+++ b/os/sb/host/sbposix.c
@@ -48,10 +48,127 @@
 /* Module local functions.                                                   */
 /*===========================================================================*/
 
+static msg_t create_descriptor(sb_ioblock_t *iop,
+                               vfs_node_c *np,
+                               uint8_t attributes) {
+  unsigned fd;
+
+  for (fd = 0U; fd < SB_CFG_FD_NUM; fd++) {
+    if (iop->vfs_nodes[fd] == NULL) {
+      iop->vfs_nodes[fd]  = np;
+      iop->attributes[fd] = attributes;
+
+      return (msg_t)fd;
+    }
+  }
+
+  return CH_RET_EMFILE;
+}
+
+static bool is_valid_descriptor(sb_ioblock_t *iop, int fd) {
+
+  return (fd >= 0) && (fd < SB_CFG_FD_NUM) && (iop->vfs_nodes[fd] != NULL);
+}
+
 /*===========================================================================*/
 /* Module exported functions.                                                */
 /*===========================================================================*/
 
+#if (SB_CFG_ENABLE_VFS == TRUE) || defined(__DOXYGEN__)
+int sb_posix_open(const char *path, int flags) {
+  sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
+  vfs_file_node_c *fnp = NULL;
+  msg_t ret;
+
+  if (!sb_is_valid_string_range(sbp, (void *)path, VFS_CFG_PATHLEN_MAX)) {
+    return CH_RET_EFAULT;
+  }
+
+  do {
+    ret = vfsDrvOpenFile(sbp->io.vfs_driver, path, (unsigned)flags, &fnp);
+    CH_BREAK_ON_ERROR(ret);
+
+    ret = create_descriptor(&sbp->io, (vfs_node_c *)fnp, 0);
+    CH_BREAK_ON_ERROR(ret);
+
+    return (int)ret;
+  } while (true);
+
+  if (fnp != NULL) {
+    vfsCloseFile(fnp);
+  }
+
+  return (int)ret;
+}
+
+int sb_posix_close(int fd) {
+  sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
+
+  if (!is_valid_descriptor(&sbp->io, fd)) {
+    return CH_RET_EBADF;
+  }
+
+  if (sbp->io.attributes[fd] == 0) {
+    vfsCloseFile((vfs_file_node_c *)sbp->io.vfs_nodes[fd]);
+  }
+  else {
+    vfsCloseDirectory((vfs_directory_node_c *)sbp->io.vfs_nodes[fd]);
+  }
+  sbp->io.vfs_nodes[fd] = NULL;
+
+  return CH_RET_SUCCESS;
+}
+
+ssize_t sb_posix_read(int fd, void *buf, size_t count) {
+  sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
+
+  if (!sb_is_valid_read_range(sbp, (void *)buf, count)) {
+    return CH_RET_EFAULT;
+  }
+
+  if (!is_valid_descriptor(&sbp->io, fd)) {
+    return CH_RET_EBADF;
+  }
+
+  if (sbp->io.attributes[fd] != 0) {
+    return CH_RET_EISDIR;
+  }
+
+  return vfsReadFile((vfs_file_node_c *)sbp->io.vfs_nodes[fd], buf, count);
+}
+
+ssize_t sb_posix_write(int fd, const void *buf, size_t count) {
+  sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
+
+  if (!sb_is_valid_write_range(sbp, (void *)buf, count)) {
+    return CH_RET_EFAULT;
+  }
+
+  if (!is_valid_descriptor(&sbp->io, fd)) {
+    return CH_RET_EBADF;
+  }
+
+  if (sbp->io.attributes[fd] != 0) {
+    return CH_RET_EISDIR;
+  }
+
+  return vfsWriteFile((vfs_file_node_c *)sbp->io.vfs_nodes[fd], buf, count);
+}
+
+off_t sb_posix_lseek(int fd, off_t offset, int whence) {
+
+  (void)offset;
+  (void)whence;
+
+  if ((fd == 0U) || (fd == 1U) || (fd == 2U)) {
+
+    return CH_RET_ESPIPE;
+  }
+
+  return CH_RET_EBADF;
+}
+
+#else /* Fallbacks for when there is no VFS.*/
 uint32_t sb_posix_open(const char *pathname, uint32_t flags) {
 
   (void)pathname;
@@ -132,5 +249,6 @@ uint32_t sb_posix_lseek(uint32_t fd, uint32_t offset, uint32_t whence) {
 
   return SB_ERR_EBADFD;
 }
+#endif
 
 /** @} */
diff --git a/os/sb/host/sbposix.h b/os/sb/host/sbposix.h
index c28c72764..ee40a38aa 100644
--- a/os/sb/host/sbposix.h
+++ b/os/sb/host/sbposix.h
@@ -28,6 +28,10 @@
 #ifndef SBPOSIX_H
 #define SBPOSIX_H
 
+#if (SB_CFG_ENABLE_VFS == TRUE) || defined(__DOXYGEN__)
+#include "vfs.h"
+#endif
+
 /*===========================================================================*/
 /* Module constants.                                                         */
 /*===========================================================================*/
@@ -44,6 +48,26 @@
 /* Module data structures and types.                                         */
 /*===========================================================================*/
 
+#if (SB_CFG_ENABLE_VFS == TRUE) || defined(__DOXYGEN__)
+/**
+ * @brief   Type of a sandbox I/O structure.
+ */
+typedef struct {
+  /**
+   * @brief   VFS driver associated to the sandbox as root.
+   */
+  vfs_driver_c                  *vfs_driver;
+  /**
+   * @brief   VFS nodes associated to file descriptors.
+   */
+  vfs_node_c                    *vfs_nodes[SB_CFG_FD_NUM];
+  /**
+   * @brief   Extra attributes added to the VFS nodes.
+   */
+  uint8_t                       attributes[SB_CFG_FD_NUM];
+} sb_ioblock_t;
+#endif
+
 /*===========================================================================*/
 /* Module macros.                                                            */
 /*===========================================================================*/
@@ -55,11 +79,11 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-  uint32_t sb_posix_open(const char *pathname, uint32_t flags);
-  uint32_t sb_posix_close(uint32_t fd);
-  uint32_t sb_posix_read(uint32_t fd, uint8_t *buf, size_t count);
-  uint32_t sb_posix_write(uint32_t fd, const uint8_t *buf, size_t count);
-  uint32_t sb_posix_lseek(uint32_t fd, uint32_t offset, uint32_t whence);
+  int sb_posix_open(const char *path, int flags);
+  int sb_posix_close(int fd);
+  ssize_t sb_posix_read(int fd, void *buf, size_t count);
+  ssize_t sb_posix_write(int fd, const void *buf, size_t count);
+  off_t sb_posix_lseek(int fd, off_t offset, int whence);
 #ifdef __cplusplus
 }
 #endif