tss: block userspace access to all I/O ports.

A userspace process (CPL=3) can access an i/o port if the bit corresponding to
the port is set to 0 in the I/O permission bitmap.

Configure the I/O permission bitmap address beyond the last valid byte in the
TSS so access to all i/o ports is blocked.

Signed-off-by: Liu Hua <sdu.liu@huawei.com>
Change-Id: I3df76980c3735491db768f7210e71703f86bb989
PiperOrigin-RevId: 257336518

2 files changed, 42 insertions, 0 deletions

diff --git a/pkg/sentry/platform/ring0/kernel_amd64.go b/pkg/sentry/platform/ring0/kernel_amd64.go
index 3577b5127..0feff8778 100644
--- a/pkg/sentry/platform/ring0/kernel_amd64.go
+++ b/pkg/sentry/platform/ring0/kernel_amd64.go
@@ -70,6 +70,14 @@ func (c *CPU) init() {
 	c.tss.ist1Lo = uint32(stackAddr)
 	c.tss.ist1Hi = uint32(stackAddr >> 32)
 
+	// Set the I/O bitmap base address beyond the last byte in the TSS
+	// to block access to the entire I/O address range.
+	//
+	// From section 18.5.2 "I/O Permission Bit Map" from Intel SDM vol1:
+	// I/O addresses not spanned by the map are treated as if they had set
+	// bits in the map.
+	c.tss.ioPerm = tssLimit + 1
+
 	// Permanently set the kernel segments.
 	c.registers.Cs = uint64(Kcode)
 	c.registers.Ds = uint64(Kdata)
diff --git a/test/syscalls/linux/exceptions.cc b/test/syscalls/linux/exceptions.cc
index 0da4c817d..370e85166 100644
--- a/test/syscalls/linux/exceptions.cc
+++ b/test/syscalls/linux/exceptions.cc
@@ -56,6 +56,26 @@ void inline Int3Normal() { asm(".byte 0xcd, 0x03\r\n"); }
 
 void inline Int3Compact() { asm(".byte 0xcc\r\n"); }
 
+void InIOHelper(int width, int value) {
+  EXPECT_EXIT(
+      {
+        switch (width) {
+          case 1:
+            asm volatile("inb %%dx, %%al" ::"d"(value) : "%eax");
+            break;
+          case 2:
+            asm volatile("inw %%dx, %%ax" ::"d"(value) : "%eax");
+            break;
+          case 4:
+            asm volatile("inl %%dx, %%eax" ::"d"(value) : "%eax");
+            break;
+          default:
+            FAIL() << "invalid input width, only 1, 2 or 4 is allowed";
+        }
+      },
+      ::testing::KilledBySignal(SIGSEGV), "");
+}
+
 TEST(ExceptionTest, Halt) {
   // In order to prevent the regular handler from messing with things (and
   // perhaps refaulting until some other signal occurs), we reset the handler to
@@ -87,6 +107,20 @@ TEST(ExceptionTest, DivideByZero) {
       ::testing::KilledBySignal(SIGFPE), "");
 }
 
+TEST(ExceptionTest, IOAccessFault) {
+  // See above.
+  struct sigaction sa = {};
+  sa.sa_handler = SIG_DFL;
+  auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGSEGV, sa));
+
+  InIOHelper(1, 0x0);
+  InIOHelper(2, 0x7);
+  InIOHelper(4, 0x6);
+  InIOHelper(1, 0xffff);
+  InIOHelper(2, 0xffff);
+  InIOHelper(4, 0xfffd);
+}
+
 TEST(ExceptionTest, Alignment) {
   SetAlignmentCheck();
   ClearAlignmentCheck();