Merge pull request #625 from besser82/topic/besser82/json-c-0.13/rdrand_fixes

json-c-0.13.x: Detect broken RDRAND during initialization.

random_seed.c

@@ -26,20 +26,11 @@
 
 static void do_cpuid(int regs[], int h)
 {
-    __asm__ __volatile__(
-#if defined __x86_64__
-                         "pushq %%rbx;\n"
-#else
-                         "pushl %%ebx;\n"
-#endif
-                         "cpuid;\n"
-#if defined __x86_64__
-                         "popq %%rbx;\n"
-#else
-                         "popl %%ebx;\n"
-#endif
-                         : "=a"(regs[0]), [ebx] "=r"(regs[1]), "=c"(regs[2]), "=d"(regs[3])
+	/* clang-format off */
+    __asm__ __volatile__("cpuid"
+                         : "=a"(regs[0]), "=b"(regs[1]), "=c"(regs[2]), "=d"(regs[3])
                          : "a"(h));
+	/* clang-format on */
 }
 
 #elif defined _MSC_VER
@@ -53,12 +44,51 @@ static void do_cpuid(int regs[], int h)
 
 #if HAS_X86_CPUID
 
-static int has_rdrand()
+static int get_rdrand_seed(void);
+
+/* Valid values are -1 (haven't tested), 0 (no), and 1 (yes). */
+static int _has_rdrand = -1;
+
+static int has_rdrand(void)
 {
-    // CPUID.01H:ECX.RDRAND[bit 30] == 1
-    int regs[4];
-    do_cpuid(regs, 1);
-    return (regs[2] & (1 << 30)) != 0;
+	if (_has_rdrand != -1)
+	{
+		return _has_rdrand;
+	}
+
+	/* CPUID.01H:ECX.RDRAND[bit 30] == 1 */
+	int regs[4];
+	do_cpuid(regs, 1);
+	if (!(regs[2] & (1 << 30)))
+	{
+		_has_rdrand = 0;
+		return 0;
+	}
+
+	/*
+	 * Some CPUs advertise RDRAND in CPUID, but return 0xFFFFFFFF
+	 * unconditionally. To avoid locking up later, test RDRAND here. If over
+	 * 3 trials RDRAND has returned the same value, declare it broken.
+	 * Example CPUs are AMD Ryzen 3000 series
+	 * and much older AMD APUs, such as the E1-1500
+	 * https://github.com/systemd/systemd/issues/11810
+	 * https://linuxreviews.org/RDRAND_stops_returning_random_values_on_older_AMD_CPUs_after_suspend
+	 */
+	_has_rdrand = 0;
+	int prev = get_rdrand_seed();
+	for (int i = 0; i < 3; i++)
+	{
+		int temp = get_rdrand_seed();
+		if (temp != prev)
+		{
+			_has_rdrand = 1;
+			break;
+		}
+
+		prev = temp;
+	}
+
+	return _has_rdrand;
 }
 
 #endif
@@ -69,17 +99,19 @@ static int has_rdrand()
 
 #define HAVE_RDRAND 1
 
-static int get_rdrand_seed()
+static int get_rdrand_seed(void)
 {
-    DEBUG_SEED("get_rdrand_seed");
-    int _eax;
-    // rdrand eax
-    __asm__ __volatile__("1: .byte 0x0F\n"
-                         "   .byte 0xC7\n"
-                         "   .byte 0xF0\n"
-                         "   jnc 1b;\n"
-                         : "=a" (_eax));
-    return _eax;
+	DEBUG_SEED("get_rdrand_seed");
+	int _eax;
+	/* rdrand eax */
+	/* clang-format off */
+	__asm__ __volatile__("1: .byte 0x0F\n"
+	                     "   .byte 0xC7\n"
+	                     "   .byte 0xF0\n"
+	                     "   jnc 1b;\n"
+	                     : "=a" (_eax));
+	/* clang-format on */
+	return _eax;
 }
 
 #endif
@@ -109,7 +141,7 @@ static int get_rdrand_seed()
 	DEBUG_SEED("get_rdrand_seed");
 	int _eax;
 retry:
-	// rdrand eax
+	/* rdrand eax */
 	__asm _emit 0x0F __asm _emit 0xC7 __asm _emit 0xF0
 	__asm jnc retry
 	__asm mov _eax, eax
@@ -178,8 +210,14 @@ static int get_dev_random_seed()
 
 #define HAVE_CRYPTGENRANDOM 1
 
+/* clang-format off */
 #include <windows.h>
+
+/* Caution: these blank lines must remain so clang-format doesn't reorder
+   includes to put windows.h after wincrypt.h */
+
 #include <wincrypt.h>
+/* clang-format on */
 #ifndef __GNUC__
 #pragma comment(lib, "advapi32.lib")
 #endif