duskos

commit 2dd2a62501c1bac35dca3cbb43d7bb28dfb3d889
parent 8fac74429fc8fe6a1f102f36faa901e720a247f8
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Wed, 10 Aug 2022 07:37:25 -0400

cvm: add memory bounds checks

Diffstat:
M
posix/vm.c
 | 
29
++++++++++++++++++++++-------

1 file changed, 22 insertions(+), 7 deletions(-)
diff --git a/posix/vm.c b/posix/vm.c
@@ -53,11 +53,18 @@ static FILE *bootfp;
 static dword lblfind = 0;
 
 // Utilities
-static byte gb(dword addr) { return vm.mem[addr]; }
+static void vmabort() { vm.PC = MEMSZ + 1; }
+static dword memchk(dword a) {
+    if (a < MEMSZ) return a;
+    printf("Out of bounds memory access! Halting");
+    vmabort();
+    return 0;
+}
+static byte gb(dword addr) { return vm.mem[memchk(addr)]; }
 static word gw(dword addr) { return gb(addr) | (gb(addr+1)<<8); }
 static dword gd(dword addr) { return gw(addr) | (gw(addr+2)<<16); }
 static dword gpc() { dword n = gd(vm.PC); vm.PC += 4; return n; }
-static void sb(dword addr, byte b) { vm.mem[addr] = b; }
+static void sb(dword addr, byte b) { vm.mem[memchk(addr)] = b; }
 static void sw(dword addr, word w) { sb(addr, w); sb(addr+1, w>>8); }
 static void sd(dword addr, dword d) { sw(addr, d); sw(addr+2, d>>16); }
 static dword ppeek() { return gd(vm.PSP); }
@@ -72,7 +79,7 @@ static dword current() { return gd(CURRENT); }
 static dword _find(dword dict, byte *name, byte slen) {
     dword a = dict;
     byte len;
-    while (a) {
+    while (memchk(a)) {
         len = gb(a-1) & 0x3f;
         if ((len == slen) && (memcmp(name, &vm.mem[a-9-len], len)==0)) {
             return a;
@@ -150,7 +157,7 @@ static void BYE() { // op: 04
 }
 
 static void BYEFAIL() { // op: 05
-    vm.PC = MEMSZ + 1;
+    vmabort();
 }
 
 static void QUIT() { // op: 06
@@ -529,7 +536,9 @@ static void MOVE() { // op: 4c
     dword u = ppop();
     dword dst = ppop();
     dword src = ppop();
-    memcpy(&vm.mem[dst], &vm.mem[src], u);
+    if (memchk(dst+u) && memchk(src+u)) {
+        memcpy(&vm.mem[dst], &vm.mem[src], u);
+    }
 }
 
 static void MOVEWR() { // op: 4d
@@ -543,7 +552,9 @@ static void MOVEWR() { // op: 4d
 static void RTYPE() { // op: 4e
     dword u = ppop();
     dword a = ppop();
-    write(STDOUT_FILENO, &vm.mem[a], u);
+    if (memchk(a+u)) {
+        write(STDOUT_FILENO, &vm.mem[a], u);
+    }
 }
 
 static void WNF() { // op: 4f
@@ -644,7 +655,9 @@ static void REQ() { // op: 54
     dword u = ppop();
     dword a2 = ppop();
     dword a1 = ppop();
-    ppush(memcmp(&vm.mem[a1], &vm.mem[a2], u) == 0);
+    if (memchk(a1+u) && memchk(a2+u)) {
+        ppush(memcmp(&vm.mem[a1], &vm.mem[a2], u) == 0);
+    }
 }
 
 // ( name 'dict -- entry-or-0 )
@@ -746,6 +759,7 @@ static void FCHILD () { // op: 5d
         vm.PC = gd(ABORT);
         return;
     }
+    if (!memchk(s+len)) return;
     strcpy(path, fsids[parent]);
     strcat(path, "/");
     strncat(path, (char*)&vm.mem[s], len);
@@ -863,6 +877,7 @@ static char *opnames[OPCNT] = {
     "_fclose", "compiling"};
 
 static void oprun1() { // run next op
+    if (!memchk(vm.PC)) return;
     byte opcode = vm.mem[vm.PC++];
     if ((opcode >= OPCNT) || (!ops[opcode])) {
         printf("Illegal opcode %02x at PC %08x\n", opcode, vm.PC-1);