Implement sysv shm.

PiperOrigin-RevId: 197058289
Change-Id: I3946c25028b7e032be4894d61acb48ac0c24d574

2 files changed, 68 insertions, 0 deletions

diff --git a/pkg/sentry/mm/BUILD b/pkg/sentry/mm/BUILD
index 39bde2be3..258389bb2 100644
--- a/pkg/sentry/mm/BUILD
+++ b/pkg/sentry/mm/BUILD
@@ -107,6 +107,7 @@ go_library(
         "pma_set.go",
         "proc_pid_maps.go",
         "save_restore.go",
+        "shm.go",
         "special_mappable.go",
         "syscalls.go",
         "vma.go",
@@ -123,6 +124,7 @@ go_library(
         "//pkg/sentry/context",
         "//pkg/sentry/fs",
         "//pkg/sentry/fs/proc/seqfile",
+        "//pkg/sentry/kernel/shm",
         "//pkg/sentry/limits",
         "//pkg/sentry/memmap",
         "//pkg/sentry/platform",
diff --git a/pkg/sentry/mm/shm.go b/pkg/sentry/mm/shm.go
new file mode 100644
index 000000000..bab137a5a
--- /dev/null
+++ b/pkg/sentry/mm/shm.go
@@ -0,0 +1,66 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mm
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/shm"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+// DetachShm unmaps a sysv shared memory segment.
+func (mm *MemoryManager) DetachShm(ctx context.Context, addr usermem.Addr) error {
+	if addr != addr.RoundDown() {
+		// "... shmaddr is not aligned on a page boundary." - man shmdt(2)
+		return syserror.EINVAL
+	}
+
+	var detached *shm.Shm
+	mm.mappingMu.Lock()
+	defer mm.mappingMu.Unlock()
+
+	// Find and remove the first vma containing an address >= addr that maps a
+	// segment originally attached at addr.
+	vseg := mm.vmas.LowerBoundSegment(addr)
+	for vseg.Ok() {
+		vma := vseg.ValuePtr()
+		if shm, ok := vma.mappable.(*shm.Shm); ok && vseg.Start() >= addr && uint64(vseg.Start()-addr) == vma.off {
+			detached = shm
+			vseg = mm.unmapLocked(ctx, vseg.Range()).NextSegment()
+			break
+		} else {
+			vseg = vseg.NextSegment()
+		}
+	}
+
+	if detached == nil {
+		// There is no shared memory segment attached at addr.
+		return syserror.EINVAL
+	}
+
+	// Remove all vmas that could have been created by the same attach.
+	end := addr + usermem.Addr(detached.EffectiveSize())
+	for vseg.Ok() && vseg.End() <= end {
+		vma := vseg.ValuePtr()
+		if vma.mappable == detached && uint64(vseg.Start()-addr) == vma.off {
+			vseg = mm.unmapLocked(ctx, vseg.Range()).NextSegment()
+		} else {
+			vseg = vseg.NextSegment()
+		}
+	}
+
+	return nil
+}