[compiler-rt] Implement getrandom interception

Summary:
Straightforward implementation of `getrandom` syscall and libc
hooks.

Test Plan: Local MSAN failures caused by uninstrumented `getrandom`
calls stop failing.

Patch by Andrew Krieger.

Reviewers: eugenis, vitalybuka

Reviewed By: vitalybuka

Subscribers: srhines, kubamracek, dberris, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D65551

llvm-svn: 367999

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc

@@ -9550,6 +9550,21 @@ INTERCEPTOR(void, sl_free, void *sl, int freeall) {
 #define INIT_SL_INIT
 #endif
 
+#if SANITIZER_INTERCEPT_GETRANDOM
+INTERCEPTOR(SSIZE_T, getrandom, void *buf, SIZE_T buflen, unsigned int flags) {
+  void *ctx;
+  COMMON_INTERCEPTOR_ENTER(ctx, getrandom, buf, buflen, flags);
+  SSIZE_T n = REAL(getrandom)(buf, buflen, flags);
+  if (n > 0) {
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, buf, n);
+  }
+  return n;
+}
+#define INIT_GETRANDOM COMMON_INTERCEPT_FUNCTION(getrandom)
+#else
+#define INIT_GETRANDOM
+#endif
+
 static void InitializeCommonInterceptors() {
 #if SI_POSIX
   static u64 metadata_mem[sizeof(MetadataHashMap) / sizeof(u64) + 1];
@@ -9848,6 +9863,7 @@ static void InitializeCommonInterceptors() {
   INIT_FDEVNAME;
   INIT_GETUSERSHELL;
   INIT_SL_INIT;
+  INIT_GETRANDOM;
 
   INIT___PRINTF_CHK;
 }

compiler-rt/lib/sanitizer_common/sanitizer_common_syscalls.inc

@@ -2873,6 +2873,18 @@ POST_SYSCALL(rt_sigaction)(long res, long signum,
     POST_WRITE(oldact, oldact_sz);
   }
 }
+
+PRE_SYSCALL(getrandom)(void *buf, uptr count, long flags) {
+  if (buf) {
+    PRE_WRITE(buf, count);
+  }
+}
+
+POST_SYSCALL(getrandom)(long res, void *buf, uptr count, long flags) {
+  if (res > 0 && buf) {
+    POST_WRITE(buf, res);
+  }
+}
 }  // extern "C"
 
 #undef PRE_SYSCALL

compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h

@@ -566,4 +566,6 @@
 #define SANITIZER_INTERCEPT_GETUSERSHELL (SI_POSIX && !SI_POSIX)
 #define SANITIZER_INTERCEPT_SL_INIT (SI_FREEBSD || SI_NETBSD)
 
+#define SANITIZER_INTERCEPT_GETRANDOM SI_LINUX
+
 #endif  // #ifndef SANITIZER_PLATFORM_INTERCEPTORS_H

compiler-rt/test/sanitizer_common/TestCases/Linux/getrandom.cpp

@@ -0,0 +1,22 @@
+// RUN: %clangxx -O2 %s -o %t && %run %t
+// UNSUPPORTED: android
+//
+
+#include <sys/types.h>
+
+#if !defined(__GLIBC_PREREQ)
+#define __GLIBC_PREREQ(a, b) 0
+#endif
+
+#if __GLIBC_PREREQ(2, 25)
+#include <sys/random.h>
+#endif
+
+int main() {
+  char buf[16];
+  ssize_t n = 1;
+#if __GLIBC_PREREQ(2, 25)
+  n = getrandom(buf, sizeof(buf), 0);
+#endif
+  return (int)(n <= 0);
+}