Add support for symlinks for regular files

Updated per first review: - enabled symlink and blocked by symlink LTP tests - fixed problems found by LTP tests - Updated files copyright - added symlink information to the documentation Signed-off-by: Bobby Marinov <[email protected]>
gramineproject · Feb 13, 2024 · ab06f66 · ab06f66
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diff --git a/Documentation/devel/features.md b/Documentation/devel/features.md
@@ -419,13 +419,13 @@ The below list is generated from the [syscall table of Linux
 - ☑ `creat()`
   <sup>[9a](#file-system-operations)</sup>
 
-- ☒ `link()`
+- ☑ `link()`
   <sup>[9d](#hard-links-and-soft-links-symbolic-links)</sup>
 
 - ☑ `unlink()`
   <sup>[9a](#file-system-operations)</sup>
 
-- ☒ `symlink()`
+- ☑ `symlink()`
   <sup>[9d](#hard-links-and-soft-links-symbolic-links)</sup>
 
 - ▣ `readlink()`
@@ -966,10 +966,10 @@ The below list is generated from the [syscall table of Linux
 - ▣ `renameat()`
   <sup>[9a](#file-system-operations)</sup>
 
-- ☒ `linkat()`
+- ☑ `linkat()`
   <sup>[9d](#hard-links-and-soft-links-symbolic-links)</sup>
 
-- ☒ `symlinkat()`
+- ☑ `symlinkat()`
   <sup>[9d](#hard-links-and-soft-links-symbolic-links)</sup>
 
 - ▣ `readlinkat()`
@@ -2068,6 +2068,9 @@ Gramine supports creating files and directories (via `creat()`, `mkdir()`, `mkdi
 calls), reading directories (via `getdents()`), deleting files and directories (via `unlink()`,
 `unlinkat()`, `rmdir()`), renaming files and directories (via `rename()` and `renameat()`).
 
+Gramine supports creating symbolic links for files and directories (via `link()`, `linkat()`,
+`symlink()` and `symlinkat()` system calls).
+
 Gramine supports read and write operations on files. Appending to files is currently unsupported.
 Writing to trusted files is prohibited.
 
@@ -2294,21 +2297,24 @@ There are two notions that must be discussed separately:
 
 1. Host OS's links: Gramine sees them as normal files. On Linux host, these links are currently
    always followed during directory/file lookup.
-2. In-Gramine links: Gramine has no support for links (i.e., applications cannot create links).
-   - There is one exception: some pseudo-files like `/proc/[pid]/cwd` and `/proc/self`.
+2. In-Gramine links: Gramine has no support for symlinks (i.e., applications can create links).
+  - The `chroot/encrypted` symlinks are passthrough symlinks that are stored on the host filesystem
+    encrypted. The `tmpfs` symlinks are stored inside the enclave memory and are not visible from
+    the outside.
+  - Hard links are only implemented for `tmpfs`. They are stored inside the enclave memory and
+    are not visible from the outside.
 
-The above means that Gramine does not implement `link()` and `symlink()` system calls. Support for
-`readlink()` system call is limited to only pseudo-files' links mentioned above.
+Support for `readlink()` system call is limited to only pseudo-files' links mentioned above.
 
-Gramine may implement hard and soft links in the future.
+Gramine may implement a complete support for hard and soft links in the future.
 
 <details><summary>Related system calls</summary>
 
-- ☒ `link()`
-- ☒ `symlink()`
+- ▣ `link()`: see note above
+- ▣ `symlink()`
 - ▣ `readlink()`: see note above
-- ☒ `linkat()`
-- ☒ `symlinkat()`
+- ▣ `linkat()`
+- ▣ `symlinkat()`
 - ▣ `readlinkat()`: see note above
 - ☒ `lchown()`
 

diff --git a/Documentation/devel/new-syscall.rst b/Documentation/devel/new-syscall.rst
@@ -53,9 +53,9 @@ call.
 4. Export new PAL calls from PAL binaries (optional)
 ----------------------------------------------------
 
-For each directory in :file:`PAL/host/`, there is a :file:`pal.map` file. This
-file lists all the symbols accessible to the library OS. The new PAL call needs
-to be listed here in order to be used by your system call implementation.
+The :file:`pal/src/pal_symbols` file lists all the symbols accessible to the library
+OS. The new PAL call needs to be listed here in order to be used by your system
+call implementation.
 
 5. Implement new PAL calls (optional)
 -------------------------------------

diff --git a/libos/src/fs/chroot/encrypted.c b/libos/src/fs/chroot/encrypted.c
@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-3.0-or-later */
 /* Copyright (C) 2022 Intel Corporation
+ * Copyright (C) 2024 Fortanix, Inc.
  *                    Paweł Marczewski <[email protected]>
+ *                    Bobby Marinov <[email protected]>
  */
 
 /*
@@ -260,7 +262,7 @@ static int chroot_encrypted_mkdir(struct libos_dentry* dent, mode_t perm) {
     /* This opens a "dir:..." URI */
     PAL_HANDLE palhdl;
     ret = PalStreamOpen(uri, PAL_ACCESS_RDONLY, HOST_PERM(perm), PAL_CREATE_ALWAYS,
-                        PAL_OPTION_PASSTHROUGH, &palhdl);
+                        PAL_OPTION_PASSTHROUGH, false, &palhdl);
     if (ret < 0) {
         ret = pal_to_unix_errno(ret);
         goto out;
@@ -292,7 +294,7 @@ static int chroot_encrypted_unlink(struct libos_dentry* dent) {
 
     PAL_HANDLE palhdl;
     ret = PalStreamOpen(uri, PAL_ACCESS_RDONLY, /*share_flags=*/0, PAL_CREATE_NEVER,
-                        PAL_OPTION_PASSTHROUGH, &palhdl);
+                        PAL_OPTION_PASSTHROUGH, false, &palhdl);
     if (ret < 0) {
         ret = pal_to_unix_errno(ret);
         goto out;
@@ -491,7 +493,7 @@ static int chroot_encrypted_chmod(struct libos_dentry* dent, mode_t perm) {
 
     PAL_HANDLE palhdl;
     ret = PalStreamOpen(uri, PAL_ACCESS_RDONLY, /*share_flags=*/0, PAL_CREATE_NEVER,
-                        PAL_OPTION_PASSTHROUGH, &palhdl);
+                        PAL_OPTION_PASSTHROUGH, false, &palhdl);
     if (ret < 0) {
         ret = pal_to_unix_errno(ret);
         goto out;

diff --git a/libos/src/fs/chroot/fs.c b/libos/src/fs/chroot/fs.c
@@ -1,7 +1,9 @@
 /* SPDX-License-Identifier: LGPL-3.0-or-later */
 /* Copyright (C) 2014 Stony Brook University
  * Copyright (C) 2021 Intel Corporation
+ * Copyright (C) 2024 Fortanix, Inc.
  *                    Paweł Marczewski <[email protected]>
+ *                    Bobby Marinov <[email protected]>
  */
 
 /*
@@ -183,14 +185,15 @@ static int chroot_lookup(struct libos_dentry* dent) {
 }
 
 /* Open a temporary read-only PAL handle for a file (used by `unlink` etc.) */
-static int chroot_temp_open(struct libos_dentry* dent, mode_t type, PAL_HANDLE* out_palhdl) {
+static int chroot_temp_open(struct libos_dentry* dent, mode_t type,
+                            bool create_delete_handle,  PAL_HANDLE* out_palhdl) {
     char* uri;
     int ret = chroot_dentry_uri(dent, type, &uri);
     if (ret < 0)
         return ret;
 
     ret = PalStreamOpen(uri, PAL_ACCESS_RDONLY, /*share_flags=*/0, PAL_CREATE_NEVER,
-                        /*options=*/0, out_palhdl);
+                        /*options=*/0, create_delete_handle, out_palhdl);
     free(uri);
     return pal_to_unix_errno(ret);
 }
@@ -202,7 +205,7 @@ static int chroot_do_open(struct libos_handle* hdl, struct libos_dentry* dent, m
 
     int ret;
 
-    char* uri;
+    char* uri = NULL;
     ret = chroot_dentry_uri(dent, type, &uri);
     if (ret < 0)
         return ret;
@@ -212,7 +215,7 @@ static int chroot_do_open(struct libos_handle* hdl, struct libos_dentry* dent, m
     enum pal_create_mode create = LINUX_OPEN_FLAGS_TO_PAL_CREATE(flags);
     pal_stream_options_t options = LINUX_OPEN_FLAGS_TO_PAL_OPTIONS(flags);
     mode_t host_perm = HOST_PERM(perm);
-    ret = PalStreamOpen(uri, access, host_perm, create, options, &palhdl);
+    ret = PalStreamOpen(uri, access, host_perm, create, options, false,  &palhdl);
     if (ret < 0) {
         ret = pal_to_unix_errno(ret);
         goto out;
@@ -348,7 +351,7 @@ int chroot_readdir(struct libos_dentry* dent, readdir_callback_t callback, void*
     char* buf = NULL;
     size_t buf_size = READDIR_BUF_SIZE;
 
-    ret = chroot_temp_open(dent, S_IFDIR, &palhdl);
+    ret = chroot_temp_open(dent, S_IFDIR, false, &palhdl);
     if (ret < 0)
         return ret;
 
@@ -409,7 +412,7 @@ int chroot_unlink(struct libos_dentry* dent) {
     int ret;
 
     PAL_HANDLE palhdl;
-    ret = chroot_temp_open(dent, dent->inode->type, &palhdl);
+    ret = chroot_temp_open(dent, dent->inode->type, true, &palhdl);
     if (ret < 0)
         return ret;
 
@@ -433,7 +436,7 @@ static int chroot_rename(struct libos_dentry* old, struct libos_dentry* new) {
         goto out;
 
     PAL_HANDLE palhdl;
-    ret = chroot_temp_open(old, old->inode->type, &palhdl);
+    ret = chroot_temp_open(old, old->inode->type, false, &palhdl);
     if (ret < 0)
         goto out;
 
@@ -450,96 +453,14 @@ static int chroot_rename(struct libos_dentry* old, struct libos_dentry* new) {
     return ret;
 }
 
-static int chroot_follow_link(struct libos_dentry* link_dent, char** out_target) {
-    assert(locked(&g_dcache_lock));
-
-    int ret;
-    char* new_uri = NULL;
-    char* target_buf = NULL;
-
-    /* get link path (no prefix) */
-    ret = chroot_dentry_uri(link_dent, S_IFREG, &new_uri);
-    if (ret < 0) {
-        goto out;
-    }
-    assert(strstartswith(new_uri, URI_PREFIX_FILE));
-    char* linkpath = new_uri + URI_PREFIX_FILE_LEN;
-    if ((*(linkpath + 0) == "./"[0]) && (*(linkpath + 1) == "./"[1])) {
-        linkpath += 2;
-    }
-
-    struct stat sb;
-    ret = PalGetLinkStats(linkpath, &sb);
-    if (ret < 0) {
-        ret = pal_to_unix_errno(ret);
-        goto out;
-    }
-
-    size_t target_sz = sb.st_size + 1;
-    target_buf = malloc(target_sz);
-    if (target_buf == NULL) {
-        ret = -ENOMEM;
-        goto out;
-    }
-
-    size_t ret_len = 0;
-    ret = PalReadLink(linkpath, target_buf, target_sz - 1, &ret_len);
-    if (ret < 0) {
-        ret = pal_to_unix_errno(ret);
-        goto out;
-    }
-
-    assert(ret_len < target_sz);
-    *(target_buf + ret_len) = '\x0';
-
-    *out_target = target_buf;
-    target_buf = NULL;
-    ret = 0;
-
-out:
-    free(target_buf);
-    free(new_uri);
-    return ret;
-}
-
-static int chroot_set_link(struct libos_dentry* link_dent, const char* targetpath,
-                           bool is_soft_link) {
-    assert(locked(&g_dcache_lock));
-
-    int ret;
-    char* new_uri = NULL;
-
-    /* get link path (no prefix) */
-    ret = chroot_dentry_uri(link_dent, S_IFREG, &new_uri);
-    if (ret < 0) {
-        goto out;
-    }
-    assert(strstartswith(new_uri, URI_PREFIX_FILE));
-    char* linkpath = new_uri + URI_PREFIX_FILE_LEN;
-    if ((*(linkpath + 0) == '.') && (*(linkpath + 1) == '/')) {
-        linkpath += 2;
-    }
-
-    ret = PalCreateLink(targetpath, linkpath, is_soft_link);
-    if (ret < 0) {
-        ret = pal_to_unix_errno(ret);
-        goto out;
-    }
-    ret = 0;
-
-out:
-    free(new_uri);
-    return ret;
-}
-
 static int chroot_chmod(struct libos_dentry* dent, mode_t perm) {
     assert(locked(&g_dcache_lock));
     assert(dent->inode);
 
     int ret;
 
     PAL_HANDLE palhdl;
-    ret = chroot_temp_open(dent, dent->inode->type, &palhdl);
+    ret = chroot_temp_open(dent, dent->inode->type, false, &palhdl);
     if (ret < 0)
         return ret;
 
@@ -589,10 +510,8 @@ struct libos_d_ops chroot_d_ops = {
     .stat    = &generic_inode_stat,
     .readdir = &chroot_readdir,
     .unlink  = &chroot_unlink,
-    .follow_link = &chroot_follow_link,
-    .set_link    = &chroot_set_link,
-    .rename      = &chroot_rename,
-    .chmod       = &chroot_chmod,
+    .rename  = &chroot_rename,
+    .chmod   = &chroot_chmod,
 };
 
 struct libos_fs chroot_builtin_fs = {

diff --git a/libos/src/fs/dev/fs.c b/libos/src/fs/dev/fs.c
@@ -65,7 +65,7 @@ static int dev_tty_open(struct libos_handle* hdl, struct libos_dentry* dent, int
 
     PAL_HANDLE palhdl;
     int ret = PalStreamOpen(uri, LINUX_OPEN_FLAGS_TO_PAL_ACCESS(flags), PSEUDO_PERM_FILE_RW,
-                            PAL_CREATE_NEVER, /*options=*/0, &palhdl);
+                            PAL_CREATE_NEVER, /*options=*/0, false, &palhdl);
     if (ret < 0) {
         free(uri);
         return pal_to_unix_errno(ret);

diff --git a/libos/src/fs/libos_fs_encrypted.c b/libos/src/fs/libos_fs_encrypted.c
@@ -157,7 +157,7 @@ static int encrypted_file_internal_open(struct libos_encrypted_file* enc, PAL_HA
     if (!pal_handle) {
         enum pal_create_mode create_mode = create ? PAL_CREATE_ALWAYS : PAL_CREATE_NEVER;
         ret = PalStreamOpen(enc->uri, PAL_ACCESS_RDWR, share_flags, create_mode,
-                            PAL_OPTION_PASSTHROUGH, &pal_handle);
+                            PAL_OPTION_PASSTHROUGH, false, &pal_handle);
         if (ret < 0) {
             log_warning("PalStreamOpen failed: %s", pal_strerror(ret));
             return pal_to_unix_errno(ret);

diff --git a/libos/src/fs/libos_namei.c b/libos/src/fs/libos_namei.c
@@ -466,6 +466,15 @@ int open_namei(struct libos_handle* hdl, struct libos_dentry* start, const char*
     }
 
     if (dent->inode && dent->inode->type == S_IFLNK) {
+        /*
+         *  If O_EXCL and O_CREAT are set, and path names a symbolic link, 
+         *  open() shall fail and set errno to [EEXIST]
+         */
+        if ((flags & O_CREAT) && (flags & O_EXCL)) {
+            ret = -EEXIST;
+            goto out;
+        }
+
         /*
          * Can happen if user specified O_NOFOLLOW, or O_TRUNC | O_EXCL. Posix requires us to fail
          * with -ELOOP when trying to open a symlink.

diff --git a/libos/src/fs/shm/fs.c b/libos/src/fs/shm/fs.c
@@ -66,7 +66,7 @@ static int shm_do_open(struct libos_handle* hdl, struct libos_dentry* dent, mode
     enum pal_create_mode create = LINUX_OPEN_FLAGS_TO_PAL_CREATE(flags);
     pal_stream_options_t options = LINUX_OPEN_FLAGS_TO_PAL_OPTIONS(flags);
     mode_t host_perm = HOST_PERM(perm);
-    ret = PalStreamOpen(uri, access, host_perm, create, options, &palhdl);
+    ret = PalStreamOpen(uri, access, host_perm, create, options, false, &palhdl);
     if (ret < 0) {
         ret = pal_to_unix_errno(ret);
         goto out;

diff --git a/libos/src/fs/tmpfs/fs.c b/libos/src/fs/tmpfs/fs.c
@@ -1,7 +1,9 @@
 /* SPDX-License-Identifier: LGPL-3.0-or-later */
 /* Copyright (C) 2021 Intel Corporation
+ * Copyright (C) 2024 Fortanix, Inc.
  *                    Li Xun <[email protected]>
  *                    Paweł Marczewski <[email protected]>
+ *                    Bobby Marinov <[email protected]>
  */
 
 /*

diff --git a/libos/src/ipc/libos_ipc.c b/libos/src/ipc/libos_ipc.c
@@ -129,7 +129,7 @@ static int ipc_connect(IDTYPE dest, struct libos_ipc_connection** conn_ptr) {
         }
         do {
             ret = PalStreamOpen(uri, PAL_ACCESS_RDONLY, /*share_flags=*/0, PAL_CREATE_IGNORED,
-                                /*options=*/0, &conn->handle);
+                                /*options=*/0, false, &conn->handle);
         } while (ret == -PAL_ERROR_INTERRUPTED);
         if (ret < 0) {
             ret = pal_to_unix_errno(ret);

diff --git a/libos/src/libos_init.c b/libos/src/libos_init.c
@@ -566,7 +566,7 @@ int create_pipe(char* name, char* uri, size_t size, PAL_HANDLE* hdl, bool use_vm
             return -ERANGE;
 
         ret = PalStreamOpen(uri, PAL_ACCESS_RDWR, /*share_flags=*/0, PAL_CREATE_IGNORED,
-                            /*options=*/0, &pipe);
+                            /*options=*/0, false, &pipe);
         if (ret < 0) {
             if (!use_vmid_for_name && ret == -PAL_ERROR_STREAMEXIST) {
                 /* tried to create a pipe with random name but it already exists */

diff --git a/libos/src/libos_pollable_event.c b/libos/src/libos_pollable_event.c
@@ -23,7 +23,7 @@ int create_pollable_event(struct libos_pollable_event* event) {
     PAL_HANDLE write_handle;
     do {
         ret = PalStreamOpen(uri, PAL_ACCESS_RDWR, /*share_flags=*/0, PAL_CREATE_IGNORED,
-                            PAL_OPTION_NONBLOCK, &write_handle);
+                            PAL_OPTION_NONBLOCK, false, &write_handle);
     } while (ret == -PAL_ERROR_INTERRUPTED);
     if (ret < 0) {
         log_error("PalStreamOpen failed: %s", pal_strerror(ret));