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Use a securely seeded global PRNG for the VM.

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It's not 2005 anymore.
This commit is contained in:
Mike Pall
2020-06-15 12:21:05 +02:00
parent 34e53736c6
commit a44f53acf5
22 changed files with 411 additions and 174 deletions
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53
src/lib_math.c
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@@ -15,6 +15,7 @@
#include "lj_obj.h"
#include "lj_lib.h"
#include "lj_vm.h"
#include "lj_prng.h"
/* ------------------------------------------------------------------------ */
@@ -105,34 +106,11 @@ LJLIB_PUSH(1e310) LJLIB_SET(huge)
** Full-period ME-CF generator with L=64, J=4, k=223, N1=49.
*/
/* PRNG state. */
struct RandomState {
uint64_t gen[4]; /* State of the 4 LFSR generators. */
int valid; /* State is valid. */
};
/* Union needed for bit-pattern conversion between uint64_t and double. */
typedef union { uint64_t u64; double d; } U64double;
/* Update generator i and compute a running xor of all states. */
#define TW223_GEN(i, k, q, s) \
z = rs->gen[i]; \
z = (((z<<q)^z) >> (k-s)) ^ ((z&((uint64_t)(int64_t)-1 << (64-k)))<<s); \
r ^= z; rs->gen[i] = z;
/* PRNG step function. Returns a double in the range 1.0 <= d < 2.0. */
LJ_NOINLINE uint64_t LJ_FASTCALL lj_math_random_step(RandomState *rs)
{
uint64_t z, r = 0;
TW223_GEN(0, 63, 31, 18)
TW223_GEN(1, 58, 19, 28)
TW223_GEN(2, 55, 24, 7)
TW223_GEN(3, 47, 21, 8)
return (r & U64x(000fffff,ffffffff)) | U64x(3ff00000,00000000);
}
/* PRNG initialization function. */
static void random_init(RandomState *rs, double d)
/* PRNG seeding function. */
static void random_seed(PRNGState *rs, double d)
{
uint32_t r = 0x11090601; /* 64-k[i] as four 8 bit constants. */
int i;
@@ -141,24 +119,22 @@ static void random_init(RandomState *rs, double d)
uint32_t m = 1u << (r&255);
r >>= 8;
u.d = d = d * 3.14159265358979323846 + 2.7182818284590452354;
if (u.u64 < m) u.u64 += m; /* Ensure k[i] MSB of gen[i] are non-zero. */
rs->gen[i] = u.u64;
if (u.u64 < m) u.u64 += m; /* Ensure k[i] MSB of u[i] are non-zero. */
rs->u[i] = u.u64;
}
rs->valid = 1;
for (i = 0; i < 10; i++)
lj_math_random_step(rs);
(void)lj_prng_u64(rs);
}
/* PRNG extract function. */
LJLIB_PUSH(top-2) /* Upvalue holds userdata with RandomState. */
LJLIB_PUSH(top-2) /* Upvalue holds userdata with PRNGState. */
LJLIB_CF(math_random) LJLIB_REC(.)
{
int n = (int)(L->top - L->base);
RandomState *rs = (RandomState *)(uddata(udataV(lj_lib_upvalue(L, 1))));
PRNGState *rs = (PRNGState *)(uddata(udataV(lj_lib_upvalue(L, 1))));
U64double u;
double d;
if (LJ_UNLIKELY(!rs->valid)) random_init(rs, 0.0);
u.u64 = lj_math_random_step(rs);
u.u64 = lj_prng_u64d(rs);
d = u.d - 1.0;
if (n > 0) {
#if LJ_DUALNUM
@@ -203,11 +179,11 @@ LJLIB_CF(math_random) LJLIB_REC(.)
}
/* PRNG seed function. */
LJLIB_PUSH(top-2) /* Upvalue holds userdata with RandomState. */
LJLIB_PUSH(top-2) /* Upvalue holds userdata with PRNGState. */
LJLIB_CF(math_randomseed)
{
RandomState *rs = (RandomState *)(uddata(udataV(lj_lib_upvalue(L, 1))));
random_init(rs, lj_lib_checknum(L, 1));
PRNGState *rs = (PRNGState *)(uddata(udataV(lj_lib_upvalue(L, 1))));
random_seed(rs, lj_lib_checknum(L, 1));
return 0;
}
@@ -217,9 +193,8 @@ LJLIB_CF(math_randomseed)
LUALIB_API int luaopen_math(lua_State *L)
{
RandomState *rs;
rs = (RandomState *)lua_newuserdata(L, sizeof(RandomState));
rs->valid = 0; /* Use lazy initialization to save some time on startup. */
PRNGState *rs = (PRNGState *)lua_newuserdata(L, sizeof(PRNGState));
lj_prng_seed_fixed(rs);
LJ_LIB_REG(L, LUA_MATHLIBNAME, math);
return 1;
}