Arm64: VDSO support for signal

The vdso is enabled, so we can use the sigreturn trampolines
the vdso provides in arch module.

Signed-off-by: Bin Lu <bin.lu@arm.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/pkg/sentry/loader/loader.go b/pkg/sentry/loader/loader.go
index 9a613d6b7..57422706d 100644
--- a/pkg/sentry/loader/loader.go
+++ b/pkg/sentry/loader/loader.go
@@ -392,6 +392,15 @@ func Load(ctx context.Context, args LoadArgs, extraAuxv []arch.AuxEntry, vdso *V
 	m.SetAuxv(auxv)
 	m.SetExecutable(d)
 
+	symbolValue, err := getSymbolValueFromVDSO("rt_sigreturn")
+	if err != nil {
+		return 0, nil, "", syserr.NewDynamic(fmt.Sprintf("Failed to find rt_sigreturn in vdso: %v", err), syserr.FromError(err).ToLinux())
+	}
+
+	// Found rt_sigretrun.
+	addr := uint64(vdsoAddr) + symbolValue - vdsoPrelink
+	m.SetVDSOSigReturn(addr)
+
 	ac.SetIP(uintptr(loaded.entry))
 	ac.SetStack(uintptr(stack.Bottom))
 
diff --git a/pkg/sentry/loader/vdso.go b/pkg/sentry/loader/vdso.go
index 52f446ed7..01eaefd26 100644
--- a/pkg/sentry/loader/vdso.go
+++ b/pkg/sentry/loader/vdso.go
@@ -15,9 +15,11 @@
 package loader
 
 import (
+	"bytes"
 	"debug/elf"
 	"fmt"
 	"io"
+	"strings"
 
 	"gvisor.dev/gvisor/pkg/abi"
 	"gvisor.dev/gvisor/pkg/context"
@@ -37,6 +39,8 @@ import (
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
+const vdsoPrelink = 0xffffffffff700000
+
 type fileContext struct {
 	context.Context
 }
@@ -218,6 +222,27 @@ type VDSO struct {
 	phdrs []elf.ProgHeader `state:".([]elfProgHeader)"`
 }
 
+// getSymbolValueFromVDSO returns the specific symbol value in vdso.so.
+func getSymbolValueFromVDSO(symbol string) (uint64, error) {
+	f, err := elf.NewFile(bytes.NewReader(vdsoBin))
+	if err != nil {
+		return 0, err
+	}
+	syms, err := f.Symbols()
+	if err != nil {
+		return 0, err
+	}
+
+	for _, sym := range syms {
+		if elf.ST_BIND(sym.Info) != elf.STB_LOCAL && sym.Section != elf.SHN_UNDEF {
+			if strings.Contains(sym.Name, symbol) {
+				return sym.Value, nil
+			}
+		}
+	}
+	return 0, fmt.Errorf("no %v in vdso.so", symbol)
+}
+
 // PrepareVDSO validates the system VDSO and returns a VDSO, containing the
 // param page for updating by the kernel.
 func PrepareVDSO(ctx context.Context, mfp pgalloc.MemoryFileProvider) (*VDSO, error) {