Refactor select syscall

1. Substitute the underlying poll OCall to select OCall to update the
timeout argument correctly.
2. Add more checks for the inputs.

src/Enclave.edl

@@ -161,6 +161,14 @@ enclave {
             int flags
         ) propagate_errno;
 
+        int occlum_ocall_select(
+            int nfds,
+            [in, out] fd_set *readfds,
+            [in, out] fd_set *writefds,
+            [in, out] fd_set *exceptfds,
+            [in, out] struct timeval *timeout
+        ) propagate_errno;
+
         void occlum_ocall_print_log(uint32_t level, [in, string] const char* msg);
         void occlum_ocall_flush_log(void);
 

src/libos/include/edl/occlum_edl_types.h

@@ -16,4 +16,9 @@ struct occlum_stdio_fds {
     int stderr_fd;
 };
 
+#define FD_SETSIZE 1024
+typedef struct {
+    unsigned long fds_bits[FD_SETSIZE / 8 / sizeof(long)];
+} fd_set;
+
 #endif /* __OCCLUM_EDL_TYPES_H__ */

src/libos/src/net/io_multiplexing/mod.rs

@@ -6,10 +6,11 @@ mod select;
 
 pub use self::epoll::{AsEpollFile, EpollCtlCmd, EpollEvent, EpollEventFlags, EpollFile};
 pub use self::poll::do_poll;
-pub use self::select::do_select;
+pub use self::select::{select, FdSetExt};
 
 use fs::{AsDevRandom, AsEvent, CreationFlags, File, FileDesc, FileRef};
 use std::any::Any;
 use std::convert::TryFrom;
 use std::fmt;
 use std::sync::atomic::spin_loop_hint;
+use time::timeval_t;

src/libos/src/net/io_multiplexing/select.rs

@@ -1,24 +1,24 @@
 use super::*;
 
-/// Forward to host `poll`
+pub fn select(
-/// (sgx_libc doesn't have `select`)
+    nfds: c_int,
-pub fn do_select(
-    nfds: usize,
     readfds: &mut libc::fd_set,
     writefds: &mut libc::fd_set,
     exceptfds: &mut libc::fd_set,
-    timeout: Option<libc::timeval>,
+    timeout: Option<&mut timeval_t>,
-) -> Result<usize> {
+) -> Result<isize> {
-    debug!("select: nfds: {}", nfds);
+    debug!("select: nfds: {} timeout: {:?}", nfds, timeout);
-    // convert libos fd to Linux fd
-    let mut host_to_libos_fd = [0; libc::FD_SETSIZE];
-    let mut polls = Vec::<libc::pollfd>::new();
 
     let current = current!();
     let file_table = current.files().lock().unwrap();
 
-    for fd in 0..nfds {
+    let mut max_host_fd = None;
-        let fd_ref = file_table.get(fd as FileDesc)?;
+    let mut host_to_libos_fd = [None; libc::FD_SETSIZE];
+    let mut unsafe_readfds = libc::fd_set::new_empty();
+    let mut unsafe_writefds = libc::fd_set::new_empty();
+    let mut unsafe_exceptfds = libc::fd_set::new_empty();
+
+    for fd in 0..(nfds as FileDesc) {
         let (r, w, e) = (
             readfds.is_set(fd),
             writefds.is_set(fd),
@@ -27,6 +27,9 @@ pub fn do_select(
         if !(r || w || e) {
             continue;
         }
+
+        let fd_ref = file_table.get(fd)?;
+
         if let Ok(socket) = fd_ref.as_unix_socket() {
             warn!("select unix socket is unimplemented, spin for read");
             readfds.clear();
@@ -39,89 +42,187 @@ pub fn do_select(
             }
 
             let (rr, ww, ee) = socket.poll()?;
+            let mut ready_num = 0;
             if r && rr {
-                readfds.set(fd);
+                readfds.set(fd)?;
+                ready_num += 1;
             }
             if w && ww {
-                writefds.set(fd);
+                writefds.set(fd)?;
+                ready_num += 1;
             }
             if e && ee {
-                writefds.set(fd);
+                exceptfds.set(fd)?;
+                ready_num += 1;
             }
-            return Ok(1);
+            return Ok(ready_num);
         }
+
         let host_fd = if let Ok(socket) = fd_ref.as_socket() {
             socket.fd()
         } else if let Ok(eventfd) = fd_ref.as_event() {
             eventfd.get_host_fd()
         } else {
             return_errno!(EBADF, "unsupported file type");
-        };
+        } as FileDesc;
 
-        host_to_libos_fd[host_fd as usize] = fd;
+        if host_fd as usize >= libc::FD_SETSIZE {
-        let mut events = 0;
+            return_errno!(EBADF, "host fd exceeds FD_SETSIZE");
+        }
+
+        // convert libos fd to host fd
+        host_to_libos_fd[host_fd as usize] = Some(fd);
+        max_host_fd = Some(max(max_host_fd.unwrap_or(0), host_fd as c_int));
         if r {
-            events |= libc::POLLIN;
+            unsafe_readfds.set(host_fd)?;
         }
         if w {
-            events |= libc::POLLOUT;
+            unsafe_writefds.set(host_fd)?;
         }
         if e {
-            events |= libc::POLLERR;
+            unsafe_exceptfds.set(host_fd)?;
         }
-
-        polls.push(libc::pollfd {
-            fd: host_fd as c_int,
-            events,
-            revents: 0,
-        });
     }
 
     // Unlock the file table as early as possible
     drop(file_table);
 
-    let timeout = match timeout {
+    let host_nfds = if let Some(fd) = max_host_fd {
-        None => -1,
+        fd + 1
-        Some(tv) => (tv.tv_sec * 1000 + tv.tv_usec / 1000) as i32,
+    } else {
+        // Set nfds to zero if no fd is monitored
+        0
     };
 
-    let (polls_ptr, polls_len) = polls.as_mut_slice().as_mut_ptr_and_len();
+    let ret = do_select_in_host(
-    let ret = try_libc!(libc::ocall::poll(polls_ptr, polls_len as u64, timeout));
+        host_nfds,
+        &mut unsafe_readfds,
+        &mut unsafe_writefds,
+        &mut unsafe_exceptfds,
+        timeout,
+    )?;
 
-    // convert fd back and write fdset
+    // convert fd back and write fdset and do ocall check
-    readfds.clear();
+    let mut ready_num = 0;
-    writefds.clear();
+    for host_fd in 0..host_nfds as FileDesc {
-    exceptfds.clear();
+        let fd_option = host_to_libos_fd[host_fd as usize];
+        let (r, w, e) = (
+            unsafe_readfds.is_set(host_fd),
+            unsafe_writefds.is_set(host_fd),
+            unsafe_exceptfds.is_set(host_fd),
+        );
+        if !(r || w || e) {
+            if let Some(fd) = fd_option {
+                readfds.unset(fd)?;
+                writefds.unset(fd)?;
+                exceptfds.unset(fd)?;
+            }
+            continue;
+        }
 
-    for poll in polls.iter() {
+        let fd = fd_option.expect("host_fd with events must have a responding libos fd");
-        let fd = host_to_libos_fd[poll.fd as usize];
+
-        if poll.revents & libc::POLLIN != 0 {
+        if r {
-            readfds.set(fd);
+            assert!(readfds.is_set(fd));
+            ready_num += 1;
+        } else {
+            readfds.unset(fd)?;
         }
-        if poll.revents & libc::POLLOUT != 0 {
+        if w {
-            writefds.set(fd);
+            assert!(writefds.is_set(fd));
+            ready_num += 1;
+        } else {
+            writefds.unset(fd)?;
         }
-        if poll.revents & libc::POLLERR != 0 {
+        if e {
-            exceptfds.set(fd);
+            assert!(exceptfds.is_set(fd));
+            ready_num += 1;
+        } else {
+            exceptfds.unset(fd)?;
         }
     }
 
-    Ok(ret as usize)
+    assert!(ready_num == ret);
+    Ok(ret)
+}
+
+fn do_select_in_host(
+    host_nfds: c_int,
+    readfds: &mut libc::fd_set,
+    writefds: &mut libc::fd_set,
+    exceptfds: &mut libc::fd_set,
+    timeout: Option<&mut timeval_t>,
+) -> Result<isize> {
+    let readfds_ptr = readfds.as_raw_ptr_mut();
+    let writefds_ptr = writefds.as_raw_ptr_mut();
+    let exceptfds_ptr = exceptfds.as_raw_ptr_mut();
+
+    let mut origin_timeout: timeval_t = Default::default();
+    let timeout_ptr = if let Some(to) = timeout {
+        origin_timeout = *to;
+        to
+    } else {
+        std::ptr::null_mut()
+    } as *mut timeval_t;
+
+    let ret = try_libc!({
+        let mut retval: c_int = 0;
+        let status = occlum_ocall_select(
+            &mut retval,
+            host_nfds,
+            readfds_ptr,
+            writefds_ptr,
+            exceptfds_ptr,
+            timeout_ptr,
+        );
+        assert!(status == sgx_status_t::SGX_SUCCESS);
+
+        retval
+    }) as isize;
+
+    if !timeout_ptr.is_null() {
+        let time_left = unsafe { *(timeout_ptr) };
+        time_left.validate()?;
+        assert!(time_left.as_duration() <= origin_timeout.as_duration());
+    }
+
+    Ok(ret)
 }
 
 /// Safe methods for `libc::fd_set`
-trait FdSetExt {
+pub trait FdSetExt {
-    fn set(&mut self, fd: usize);
+    fn new_empty() -> Self;
+    fn unset(&mut self, fd: FileDesc) -> Result<()>;
+    fn is_set(&self, fd: FileDesc) -> bool;
+    fn set(&mut self, fd: FileDesc) -> Result<()>;
     fn clear(&mut self);
-    fn is_set(&mut self, fd: usize) -> bool;
+    fn is_empty(&self) -> bool;
+    fn as_raw_ptr_mut(&mut self) -> *mut Self;
 }
 
 impl FdSetExt for libc::fd_set {
-    fn set(&mut self, fd: usize) {
+    fn new_empty() -> Self {
-        assert!(fd < libc::FD_SETSIZE);
+        unsafe { core::mem::zeroed() }
+    }
+
+    fn unset(&mut self, fd: FileDesc) -> Result<()> {
+        if fd as usize >= libc::FD_SETSIZE {
+            return_errno!(EINVAL, "fd exceeds FD_SETSIZE");
+        }
+        unsafe {
+            libc::FD_CLR(fd as c_int, self);
+        }
+        Ok(())
+    }
+
+    fn set(&mut self, fd: FileDesc) -> Result<()> {
+        if fd as usize >= libc::FD_SETSIZE {
+            return_errno!(EINVAL, "fd exceeds FD_SETSIZE");
+        }
         unsafe {
             libc::FD_SET(fd as c_int, self);
         }
+        Ok(())
     }
 
     fn clear(&mut self) {
@@ -130,8 +231,36 @@ impl FdSetExt for libc::fd_set {
         }
     }
 
-    fn is_set(&mut self, fd: usize) -> bool {
+    fn is_set(&self, fd: FileDesc) -> bool {
-        assert!(fd < libc::FD_SETSIZE);
+        if fd as usize >= libc::FD_SETSIZE {
-        unsafe { libc::FD_ISSET(fd as c_int, self) }
+            return false;
+        }
+        unsafe { libc::FD_ISSET(fd as c_int, self as *const Self as *mut Self) }
+    }
+
+    fn is_empty(&self) -> bool {
+        let set = unsafe {
+            std::slice::from_raw_parts(self as *const Self as *const u64, libc::FD_SETSIZE / 64)
+        };
+        set.iter().all(|&x| x == 0)
+    }
+
+    fn as_raw_ptr_mut(&mut self) -> *mut Self {
+        if self.is_empty() {
+            std::ptr::null_mut()
+        } else {
+            self as *mut libc::fd_set
+        }
     }
 }
+
+extern "C" {
+    fn occlum_ocall_select(
+        ret: *mut c_int,
+        nfds: c_int,
+        readfds: *mut libc::fd_set,
+        writefds: *mut libc::fd_set,
+        exceptfds: *mut libc::fd_set,
+        timeout: *mut timeval_t,
+    ) -> sgx_status_t;
+}

src/libos/src/net/syscalls.rs

@@ -1,10 +1,11 @@
 use super::*;
 
-use super::io_multiplexing::{AsEpollFile, EpollCtlCmd, EpollEventFlags, EpollFile};
+use super::io_multiplexing::{AsEpollFile, EpollCtlCmd, EpollEventFlags, EpollFile, FdSetExt};
 use fs::{CreationFlags, File, FileDesc, FileRef};
 use misc::resource_t;
 use process::Process;
 use std::convert::TryFrom;
+use time::timeval_t;
 use util::mem_util::from_user;
 
 pub fn do_sendmsg(fd: c_int, msg_ptr: *const msghdr, flags_c: c_int) -> Result<isize> {
@@ -129,45 +130,59 @@ pub fn do_select(
     readfds: *mut libc::fd_set,
     writefds: *mut libc::fd_set,
     exceptfds: *mut libc::fd_set,
-    timeout: *const libc::timeval,
+    timeout: *mut timeval_t,
 ) -> Result<isize> {
     // check arguments
-    if nfds < 0 || nfds >= libc::FD_SETSIZE as c_int {
+    let soft_rlimit_nofile = current!()
-        return_errno!(EINVAL, "nfds is negative or exceeds the resource limit");
+        .rlimits()
+        .lock()
+        .unwrap()
+        .get(resource_t::RLIMIT_NOFILE)
+        .get_cur();
+    if nfds < 0 || nfds > libc::FD_SETSIZE as i32 || nfds as u64 > soft_rlimit_nofile {
+        return_errno!(
+            EINVAL,
+            "nfds is negative or exceeds the resource limit or FD_SETSIZE"
+        );
     }
-    let nfds = nfds as usize;
 
-    let mut zero_fds0: libc::fd_set = unsafe { core::mem::zeroed() };
+    // Select handles empty set and null in the same way
-    let mut zero_fds1: libc::fd_set = unsafe { core::mem::zeroed() };
+    // TODO: Elegently handle the empty fd_set without allocating redundant fd_set
-    let mut zero_fds2: libc::fd_set = unsafe { core::mem::zeroed() };
+    let mut empty_set_for_read = libc::fd_set::new_empty();
+    let mut empty_set_for_write = libc::fd_set::new_empty();
+    let mut empty_set_for_except = libc::fd_set::new_empty();
 
     let readfds = if !readfds.is_null() {
         from_user::check_mut_ptr(readfds)?;
         unsafe { &mut *readfds }
     } else {
-        &mut zero_fds0
+        &mut empty_set_for_read
     };
     let writefds = if !writefds.is_null() {
         from_user::check_mut_ptr(writefds)?;
         unsafe { &mut *writefds }
     } else {
-        &mut zero_fds1
+        &mut empty_set_for_write
     };
     let exceptfds = if !exceptfds.is_null() {
         from_user::check_mut_ptr(exceptfds)?;
         unsafe { &mut *exceptfds }
     } else {
-        &mut zero_fds2
+        &mut empty_set_for_except
     };
-    let timeout = if !timeout.is_null() {
+
+    let timeout_option = if !timeout.is_null() {
         from_user::check_ptr(timeout)?;
-        Some(unsafe { timeout.read() })
+        unsafe {
+            (*timeout).validate()?;
+            Some(&mut *timeout)
+        }
     } else {
         None
     };
 
-    let n = io_multiplexing::do_select(nfds, readfds, writefds, exceptfds, timeout)?;
+    let ret = io_multiplexing::select(nfds, readfds, writefds, exceptfds, timeout_option)?;
-    Ok(n as isize)
+    Ok(ret)
 }
 
 pub fn do_poll(fds: *mut libc::pollfd, nfds: libc::nfds_t, timeout: c_int) -> Result<isize> {

src/libos/src/syscall/mod.rs

@@ -98,7 +98,7 @@ macro_rules! process_syscall_table_with_callback {
             (Writev = 20) => do_writev(fd: FileDesc, iov: *const iovec_t, count: i32),
             (Access = 21) => do_access(path: *const i8, mode: u32),
             (Pipe = 22) => do_pipe(fds_u: *mut i32),
-            (Select = 23) => do_select(nfds: c_int, readfds: *mut libc::fd_set, writefds: *mut libc::fd_set, exceptfds: *mut libc::fd_set, timeout: *const libc::timeval),
+            (Select = 23) => do_select(nfds: c_int, readfds: *mut libc::fd_set, writefds: *mut libc::fd_set, exceptfds: *mut libc::fd_set, timeout: *mut timeval_t),
             (SchedYield = 24) => do_sched_yield(),
             (Mremap = 25) => do_mremap(old_addr: usize, old_size: usize, new_size: usize, flags: i32, new_addr: usize),
             (Msync = 26) => handle_unsupported(),

src/pal/include/edl/occlum_edl_types.h

@@ -2,6 +2,7 @@
 #define __OCCLUM_EDL_TYPES__
 
 #include <time.h>               // import struct timespec
+#include <sys/select.h>         // import fd_set
 #include <sys/time.h>           // import struct timeval
 #include <sys/uio.h>            // import struct iovec
 #include <occlum_pal_api.h>     // import occlum_stdio_fds

src/pal/src/ocalls/net.c

@@ -1,4 +1,5 @@
 #include <sys/types.h>
+#include <sys/select.h>
 #include <sys/socket.h>
 #include <stddef.h>
 #include "ocalls.h"
@@ -53,3 +54,11 @@ ssize_t occlum_ocall_recvmsg(int sockfd,
     *msg_flags_recv = msg.msg_flags;
     return ret;
 }
+
+int occlum_ocall_select(int nfds,
+                        fd_set *readfds,
+                        fd_set *writefds,
+                        fd_set *exceptfds,
+                        struct timeval *timeout) {
+    return select(nfds, readfds, writefds, exceptfds, timeout);
+}

test/eventfd/main.c

@@ -145,7 +145,8 @@ int test_read_write() {
 }
 
 int test_select_with_socket() {
-    fd_set wfds;
+    fd_set rfds, wfds;
+    int ret = 0;
 
     struct timeval tv = { .tv_sec = 60, .tv_usec = 0 };
 
@@ -155,15 +156,24 @@ int test_select_with_socket() {
         THROW_ERROR("failed to create files");
     }
 
+    FD_ZERO(&rfds);
     FD_ZERO(&wfds);
+    FD_SET(sock, &rfds);
     FD_SET(sock, &wfds);
+    FD_SET(event_fd, &rfds);
     FD_SET(event_fd, &wfds);
-
+    ret = select(sock > event_fd? sock + 1: event_fd + 1, &rfds, &wfds, NULL, &tv);
-    if (select(sock > event_fd? sock + 1: event_fd + 1, NULL, &wfds, NULL, &tv) <= 0) {
+    if (ret != 3) {
         close_files(2, sock, event_fd);
         THROW_ERROR("select failed");
     }
 
+    if (FD_ISSET(event_fd, &rfds) == 1 || FD_ISSET(event_fd, &wfds) == 0 ||
+        FD_ISSET(sock, &rfds) == 0 || FD_ISSET(sock, &wfds) == 0) {
+        close_files(2, sock, event_fd);
+        THROW_ERROR("bad select return");
+    }
+
     close_files(2, sock, event_fd);
     return 0;
 }