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 <[email protected]>
gristlabs · Apr 17, 2020 · fe001ed · fe001ed
1 parent 0dd9ee0
commit fe001ed
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Showing 5 changed files with 54 additions and 18 deletions.
diff --git 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
@@ -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) {

diff --git a/vdso/syscalls.h b/vdso/syscalls.h
@@ -26,6 +26,9 @@
 #include <stddef.h>
 #include <sys/types.h>
 
+#define __stringify_1(x...)     #x
+#define __stringify(x...)       __stringify_1(x)
+
 namespace vdso {
 
 #if __x86_64__
@@ -51,20 +54,13 @@ static inline int sys_getcpu(unsigned* cpu, unsigned* node,
   return num;
 }
 
-#elif __aarch64__
-
-static inline int sys_rt_sigreturn(void) {
-  int num = __NR_rt_sigreturn;
-
-  asm volatile(
-      "mov x8, %0\n"
-      "svc #0    \n"
-      : "+r"(num)
-      :
-      :);
-  return num;
+static inline void sys_rt_sigreturn(void) {
+  asm volatile("movl $" __stringify(__NR_rt_sigreturn)", %eax \n"
+               "syscall \n");
 }
 
+#elif __aarch64__
+
 static inline int sys_clock_gettime(clockid_t _clkid, struct timespec* _ts) {
   register struct timespec* ts asm("x1") = _ts;
   register clockid_t clkid asm("x0") = _clkid;
@@ -91,6 +87,11 @@ static inline int sys_clock_getres(clockid_t _clkid, struct timespec* _ts) {
   return ret;
 }
 
+static inline void sys_rt_sigreturn(void) {
+  asm volatile("mov x8, #" __stringify(__NR_rt_sigreturn)" \n"
+               "svc #0 \n");
+}
+
 #else
 #error "unsupported architecture"
 #endif

diff --git a/vdso/vdso.cc b/vdso/vdso.cc
@@ -69,6 +69,12 @@ int __common_gettimeofday(struct timeval* tv, struct timezone* tz) {
 }
 }  // namespace
 
+// __kernel_rt_sigreturn() implements rt_sigreturn()
+extern "C" void __kernel_rt_sigreturn(unsigned long unused) {
+  // No optimizations yet, just make the real system call.
+  sys_rt_sigreturn();
+}
+
 #if __x86_64__
 
 // __vdso_clock_gettime() implements clock_gettime()
@@ -139,12 +145,6 @@ extern "C" int __kernel_clock_getres(clockid_t clock, struct timespec* res) {
   return ret;
 }
 
-// __kernel_rt_sigreturn() implements gettimeofday()
-extern "C" int __kernel_rt_sigreturn(unsigned long unused) {
-  // No optimizations yet, just make the real system call.
-  return sys_rt_sigreturn();
-}
-
 #else
 #error "unsupported architecture"
 #endif

diff --git a/vdso/vdso_amd64.lds b/vdso/vdso_amd64.lds
@@ -95,6 +95,7 @@ VERSION {
     __vdso_getcpu;
     time;
     __vdso_time;
+    __kernel_rt_sigreturn;
 
   local: *;
   };