Hook getrandom()

5 files changed, 38 insertions, 9 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7d32ade5..268667d8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@
 * Autodetect game engine and enforce some settings
 * [ImGui] When detached, game window can be resized
 * Disable a dotnet speed check (#590)
+* Hook getrandom()
 
 ### Changed
 
diff --git a/src/library/fileio/URandom.cpp b/src/library/fileio/URandom.cpp
index 6c9ac2fa..2d250ddd 100644
--- a/src/library/fileio/URandom.cpp
+++ b/src/library/fileio/URandom.cpp
@@ -35,21 +35,28 @@ static int writefd = -1;
 static FILE* stream = nullptr;
 static uint64_t prng_state = 0;
 
-static void urandom_handler(int signum)
+uint64_t urandom_rand()
 {
-    debuglogstdio(LCF_FILEIO | LCF_RANDOM, "Filling urandom fd");
     if (!prng_state)
         prng_state = Global::shared_config.initial_time_sec;
     
+    /* Use xorshift64* algorithm to generate pseudo-random values */
+    uint64_t r = prng_state;	/* The state must be seeded with a nonzero value. */
+    r ^= r >> 12;
+    r ^= r << 25;
+    r ^= r >> 27;
+    prng_state = r;
+    r *= 0x2545F4914F6CDD1DULL;
+    return r;
+}
+
+static void urandom_handler(int signum)
+{
+    debuglogstdio(LCF_FILEIO | LCF_RANDOM, "Filling urandom fd");
+    
     int err = 0;
     do {
-        /* Use xorshift64* algorithm to generate pseudo-random values */
-        uint64_t r = prng_state;	/* The state must be seeded with a nonzero value. */
-    	r ^= r >> 12;
-    	r ^= r << 25;
-    	r ^= r >> 27;
-    	prng_state = r;
-        r *= 0x2545F4914F6CDD1DULL;
+        uint64_t r = urandom_rand();
         err = write(writefd, &r, sizeof(uint64_t));
     } while (err != -1);
 }
diff --git a/src/library/fileio/URandom.h b/src/library/fileio/URandom.h
index 0195649f..711f0d39 100644
--- a/src/library/fileio/URandom.h
+++ b/src/library/fileio/URandom.h
@@ -21,9 +21,13 @@
 #define LIBTAS_URANDOM_H_INCLUDED
 
 #include <cstdio>
+#include <cstdint>
 
 namespace libtas {
 
+/* Generate a single random 64-bit value */ 
+uint64_t urandom_rand();
+
 /* Creates a fd implementing our own deterministic /dev/urandom */
 int urandom_create_fd();
 
diff --git a/src/library/general/randomwrappers.cpp b/src/library/general/randomwrappers.cpp
index e5aaf672..7af2d666 100644
--- a/src/library/general/randomwrappers.cpp
+++ b/src/library/general/randomwrappers.cpp
@@ -21,12 +21,24 @@
 
 #include "logging.h"
 #include "hook.h"
+#include "fileio/URandom.h"
 
 namespace libtas {
 
 DEFINE_ORIG_POINTER(random)
 DEFINE_ORIG_POINTER(rand)
 
+/* Override */ ssize_t getrandom (void *buffer, size_t length, unsigned int flags)
+{
+    char* buf = static_cast<char*>(buffer);
+    /* We use the same PRNG as in URandom, because it is supposed to get the same values */
+    for (size_t l = 0; l < length; l += 8) {
+        uint64_t r = urandom_rand();
+        memcpy(buf+l, &r, std::min((size_t)8, length-l));
+    }
+    return length;
+}
+
 /* Override */ long int random (void) __THROW
 {
     static int count = 0;
diff --git a/src/library/general/randomwrappers.h b/src/library/general/randomwrappers.h
index 38b93f75..91f7272c 100644
--- a/src/library/general/randomwrappers.h
+++ b/src/library/general/randomwrappers.h
@@ -24,9 +24,14 @@
 
 #include <cstdint>
 #include <cstddef>
+#include <sys/types.h> // ssize_t
 
 namespace libtas {
 
+/* Write LENGTH bytes of randomness starting at BUFFER.  Return the
+   number of bytes written, or -1 on error.  */
+OVERRIDE ssize_t getrandom (void *buffer, size_t length, unsigned int flags);
+
 /* These are the functions that actually do things.  The `random', `srandom',
    `initstate' and `setstate' functions are those from BSD Unices.
    The `rand' and `srand' functions are required by the ANSI standard.