allow plugin to query for KVM extensions

The guest may need to check for KVM extensions before blindly using
them.

TEST=cargo test --features plugin; cargo test -p kvm; ./build_test
BUG=chromium:800626

Change-Id: If87b928753cd71adeabac4fc7732c3fce7265834
Reviewed-on: https://chromium-review.googlesource.com/906008
Commit-Ready: Zach Reizner <zachr@chromium.org>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>

Cargo.lock

@@ -18,7 +18,7 @@ name = "crosvm"
 version = "0.1.0"
 dependencies = [
  "byteorder 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "crosvm_plugin 0.9.0",
+ "crosvm_plugin 0.10.0",
  "data_model 0.1.0",
  "devices 0.1.0",
  "io_jail 0.1.0",
@@ -28,7 +28,7 @@ dependencies = [
  "kvm_sys 0.1.0",
  "libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
  "net_util 0.1.0",
- "plugin_proto 0.9.0",
+ "plugin_proto 0.10.0",
  "protobuf 1.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "qcow 0.1.0",
  "qcow_utils 0.1.0",
@@ -41,12 +41,12 @@ dependencies = [
 
 [[package]]
 name = "crosvm_plugin"
-version = "0.9.0"
+version = "0.10.0"
 dependencies = [
  "kvm 0.1.0",
  "kvm_sys 0.1.0",
  "libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
- "plugin_proto 0.9.0",
+ "plugin_proto 0.10.0",
  "protobuf 1.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "sys_util 0.1.0",
 ]
@@ -160,7 +160,7 @@ dependencies = [
 
 [[package]]
 name = "plugin_proto"
-version = "0.9.0"
+version = "0.10.0"
 dependencies = [
  "gcc 0.3.54 (registry+https://github.com/rust-lang/crates.io-index)",
  "protobuf 1.4.3 (registry+https://github.com/rust-lang/crates.io-index)",

crosvm_plugin/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "crosvm_plugin"
-version = "0.9.0"
+version = "0.10.0"
 authors = ["The Chromium OS Authors"]
 
 [lib]

crosvm_plugin/crosvm.h

@@ -47,7 +47,7 @@ extern "C" {
  * do not indicate anything about what version of crosvm is running.
  */
 #define CROSVM_API_MAJOR 0
-#define CROSVM_API_MINOR 9
+#define CROSVM_API_MINOR 10
 #define CROSVM_API_PATCH 0
 
 enum crosvm_address_space {
@@ -108,6 +108,12 @@ int crosvm_destroy_connection(struct crosvm**);
  */
 int crosvm_get_shutdown_eventfd(struct crosvm*);
 
+/*
+ * Gets a bool indicating if a KVM_CAP_* enum is supported on this VM
+ */
+int crosvm_check_extension(struct crosvm*, uint32_t __extension,
+                           bool *__has_extension);
+
 /*
  * Registers a range in the given address space that, when accessed, will block
  * and wait for a crosvm_vcpu_resume call.

crosvm_plugin/src/lib.rs

@@ -233,6 +233,16 @@ impl crosvm {
         }
     }
 
+    fn check_extension(&mut self, extension: u32) -> result::Result<bool, c_int> {
+        let mut r = MainRequest::new();
+        r.mut_check_extension().extension = extension;
+        let (response, _) = self.main_transaction(&r, &[])?;
+        if !response.has_check_extension() {
+            return Err(-EPROTO);
+        }
+        Ok(response.get_check_extension().has_extension)
+    }
+
     fn reserve_range(&mut self, space: u32, start: u64, length: u64) -> result::Result<(), c_int> {
         let mut r = MainRequest::new();
         {
@@ -809,6 +819,21 @@ pub unsafe extern "C" fn crosvm_get_shutdown_eventfd(self_: *mut crosvm) -> c_in
     }
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn crosvm_check_extension(self_: *mut crosvm,
+                                                extension: u32,
+                                                has_extension: *mut bool)
+                                                -> c_int {
+    let self_ = &mut (*self_);
+    match self_.check_extension(extension) {
+        Ok(supported) => {
+            *has_extension = supported;
+            0
+        }
+        Err(e) => e,
+    }
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn crosvm_reserve_range(self_: *mut crosvm,
                                               space: u32,

kvm/src/lib.rs

@@ -223,6 +223,18 @@ impl Vm {
         }
     }
 
+    /// Checks if a particular `Cap` is available.
+    ///
+    /// This is distinct from the `Kvm` version of this method because the some extensions depend on
+    /// the particular `Vm` existence. This method is encouraged by the kernel because it more
+    /// accurately reflects the usable capabilities.
+    pub fn check_extension(&self, c: Cap) -> bool {
+        // Safe because we know that our file is a KVM fd and that the extension is one of the ones
+        // defined by kernel.
+        unsafe { ioctl_with_val(self, KVM_CHECK_EXTENSION(), c as c_ulong) == 1 }
+    }
+
+
     /// Inserts the given `MemoryMapping` into the VM's address space at `guest_addr`.
     ///
     /// The slot that was assigned the device memory mapping is returned on success. The slot can be
@@ -1022,6 +1034,16 @@ mod tests {
         assert!(!kvm.check_extension(Cap::S390UserSigp));
     }
 
+    #[test]
+    fn check_vm_extension() {
+        let kvm = Kvm::new().unwrap();
+        let gm = GuestMemory::new(&vec![(GuestAddress(0), 0x1000)]).unwrap();
+        let vm = Vm::new(&kvm, gm).unwrap();
+        assert!(vm.check_extension(Cap::UserMemory));
+        // I assume nobody is testing this on s390
+        assert!(!vm.check_extension(Cap::S390UserSigp));
+    }
+
     #[test]
     fn add_memory() {
         let kvm = Kvm::new().unwrap();

plugin_proto/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "plugin_proto"
-version = "0.9.0"
+version = "0.10.0"
 authors = ["The Chromium OS Authors"]
 build = "build.rs"
 

plugin_proto/protos/plugin.proto

@@ -68,6 +68,10 @@ message MainRequest {
 
     message GetShutdownEventfd {}
 
+    message CheckExtension {
+        uint32 extension = 1;
+    }
+
     message ReserveRange {
         AddressSpace space = 1;
         uint64 start = 2;
@@ -126,13 +130,14 @@ message MainRequest {
         Destroy destroy = 2;
         NewConnection new_connection = 3;
         GetShutdownEventfd get_shutdown_eventfd = 4;
-        ReserveRange reserve_range = 5;
-        SetIrq set_irq = 6;
-        SetIrqRouting set_irq_routing = 7;
-        SetIdentityMapAddr set_identity_map_addr = 8;
-        PauseVcpus pause_vcpus = 9;
-        GetVcpus get_vcpus = 10;
-        Start start = 11;
+        CheckExtension check_extension = 5;
+        ReserveRange reserve_range = 6;
+        SetIrq set_irq = 7;
+        SetIrqRouting set_irq_routing = 8;
+        SetIdentityMapAddr set_identity_map_addr = 9;
+        PauseVcpus pause_vcpus = 10;
+        GetVcpus get_vcpus = 11;
+        Start start = 12;
         // Method for a Memory type object for retrieving the dirty bitmap. Only valid if the memory
         // object was created with dirty_log set.
         MemoryDirtyLog dirty_log = 101;
@@ -148,6 +153,9 @@ message MainResponse {
     // requests and responses independent of the other sockets.
     message NewConnection {}
     message GetShutdownEventfd {}
+    message CheckExtension {
+        bool has_extension = 1;
+    }
     message ReserveRange {}
     message SetIrq {}
     message SetIrqRouting {}
@@ -170,13 +178,14 @@ message MainResponse {
         Destroy destroy = 3;
         NewConnection new_connection = 4;
         GetShutdownEventfd get_shutdown_eventfd = 5;
-        ReserveRange reserve_range = 6;
-        SetIrq set_irq = 7;
-        SetIrqRouting set_irq_routing = 8;
-        SetIdentityMapAddr set_identity_map_addr = 9;
-        PauseVcpus pause_vcpus = 10;
-        GetVcpus get_vcpus = 11;
-        Start start = 12;
+        CheckExtension check_extension = 6;
+        ReserveRange reserve_range = 7;
+        SetIrq set_irq = 8;
+        SetIrqRouting set_irq_routing = 9;
+        SetIdentityMapAddr set_identity_map_addr = 10;
+        PauseVcpus pause_vcpus = 11;
+        GetVcpus get_vcpus = 12;
+        Start start = 13;
         MemoryDirtyLog dirty_log = 101;
     }
 }

src/plugin/process.rs

@@ -5,6 +5,7 @@
 use std::collections::hash_map::{HashMap, Entry, VacantEntry};
 use std::env::set_var;
 use std::fs::File;
+use std::mem::transmute;
 use std::net::Shutdown;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::os::unix::net::UnixDatagram;
@@ -483,6 +484,14 @@ impl Process {
             response.mut_get_shutdown_eventfd();
             response_fds.push(self.kill_evt.as_raw_fd());
             Ok(())
+        } else if request.has_check_extension() {
+            // Safe because the Cap enum is not read by the check_extension method. In that method,
+            // cap is cast back to an integer and fed to an ioctl. If the extension name is actually
+            // invalid, the kernel will safely reject the extension under the assumption that the
+            // capability is legitimately unsupported.
+            let cap = unsafe { transmute(request.get_check_extension().extension) };
+            response.mut_check_extension().has_extension = vm.check_extension(cap);
+            Ok(())
         } else if request.has_reserve_range() {
             response.mut_reserve_range();
             self.handle_reserve_range(request.get_reserve_range())

tests/plugin_extensions.c

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2018 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/memfd.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "crosvm.h"
+
+int main(int argc, char** argv) {
+    struct crosvm *crosvm;
+    int ret = crosvm_connect(&crosvm);
+    if (ret) {
+        fprintf(stderr, "failed to connect to crosvm: %d\n", ret);
+        return 1;
+    }
+
+    bool supported;
+    ret = crosvm_check_extension(crosvm, KVM_CAP_IRQCHIP, &supported);
+    if (ret) {
+        fprintf(stderr, "failed to check for KVM extension: %d\n", ret);
+        return 1;
+    }
+    if (!supported) {
+        fprintf(stderr, "expected KVM extension to be supported\n");
+        return 1;
+    }
+
+    // Assume s390 extensions aren't supported because we shouldn't be running on one.
+    ret = crosvm_check_extension(crosvm, KVM_CAP_S390_PSW, &supported);
+    if (ret) {
+        fprintf(stderr, "failed to check for KVM extension: %d\n", ret);
+        return 1;
+    }
+    if (supported) {
+        fprintf(stderr, "unexpected KVM extension is supported\n");
+        return 1;
+    }
+
+    return 0;
+}

tests/plugins.rs

@@ -225,6 +225,11 @@ fn test_irqfd() {
     test_plugin(include_str!("plugin_irqfd.c"));
 }
 
+#[test]
+fn test_extensions() {
+    test_plugin(include_str!("plugin_extensions.c"));
+}
+
 #[test]
 fn test_debugregs() {
     let mini_plugin = MiniPlugin {