duskos

commit 60edd420cc32c189d716d5a847019702ab4f7563
parent 18d90eef8d5046602150136d377784a69758e0ac
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Mon,  8 May 2023 22:40:55 -0400

posix/vm: add memory protection mechanism

very useful for debugging memory corruption.

Diffstat:
M
posix/vm.c
 | 
21
+++++++++++++++++----

1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/posix/vm.c b/posix/vm.c
@@ -91,6 +91,8 @@ struct VM {
 	dword W;  // W is PS top
 	dword A;
 	dword T; // tmp register. not directly addressable
+	dword mprotect; // halt when protected memory is changed
+	dword mprotectsz;
 	byte Z;
 	byte C;
 	byte SC; // signed C
@@ -111,10 +113,17 @@ static dword mainaddr;
 static void vmabort() { vm.PC = MEMSZ + 1; }
 static dword memchk(dword a) {
 	if (a < MEMSZ) return a;
-	printf("Out of bounds memory access! Halting");
+	printf("Out of bounds memory access! Halting\n");
 	vmabort();
 	return 0;
 }
+static dword memchkmut(dword a) {
+	if ((a >= vm.mprotect) && (a < vm.mprotect + vm.mprotectsz)) {
+		printf("Access to protected memory! Halting\n");
+		vmabort();
+		return 0;
+	} else { return a; }
+}
 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); }
@@ -130,7 +139,7 @@ static dword gdr(dword addr) {
 }
 static dword gpc() { dword n = gd(vm.PC); vm.PC += 4; return n; }
 static byte gpcb() { dword n = gb(vm.PC); vm.PC++; return n; }
-static void sb(dword addr, byte b) { vm.mem[memchk(addr)] = b; }
+static void sb(dword addr, byte b) { vm.mem[memchkmut(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 void sdr(dword addr, dword d) {
@@ -595,6 +604,8 @@ static void DBG() {
 	printf("RS "); _stackdump(vm.RSP, RSTOP);
 }
 static void USLEEP() { usleep(ppop()); }
+// ( a u -- )
+static void MPROTECT() { vm.mprotectsz = ppop(); vm.mprotect = ppop(); }
 
 // 0x60
 static void WCHECKZ() { vm.Z = !vm.W; }
@@ -894,7 +905,7 @@ static void (*ops[OPCNT])() = {
 	STACKCHK, COMPWORD, RUNWORD, COMPILING, STARTCOMP, STOPCOMP, RSADDWR, COMPOP,
 	ALIGN4, ENTRY, CODE, CODE16, CODE8, COMPBINOP, NULL, NULL,
 	WBINOP, WBINOP16, WBINOP8, DIVMOD, NULL, LT, NEG, NULL,
-	BYE, BYEFAIL, QUIT, ABORT_, DBG, USLEEP, NULL, NULL,
+	BYE, BYEFAIL, QUIT, ABORT_, DBG, USLEEP, MPROTECT, NULL,
 	NULL, NULL, NULL, NULL, NULL, WCHECKZ, STOREC, ACHECKZ,
 	FCHILD, FOPEN, FREADBUF, FCLOSE, FINFO, FITER, NULL, FSEEK,
 	MOUNTDRV, UNMOUNTDRV, DRVRD, DRVWR, NULL, NULL, NULL, NULL,
@@ -937,7 +948,7 @@ static char *opnames[OPCNT-0x28] = {
 	"stack?", "compword", "runword", "compiling", "]", NULL, "rs+,", NULL,
 	"align4", "entry", "code", "code16b", "code8b", NULL, NULL, NULL,
 	NULL, NULL, NULL, "/mod", NULL, "<", NULL, NULL,
-	"bye", "byefail", "quit", "(abort)", "dbg", "_usleep", NULL, NULL,
+	"bye", "byefail", "quit", "(abort)", "dbg", "_usleep", "mprotect", NULL,
 	NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
 	"_fchild", "_fopen", "_freadbuf", "_fclose", "_finfo", "_fiter", NULL, "_fseek",
 	"_mountdrv", "_unmountdrv", "_drv@", "_drv!", NULL, NULL, NULL, NULL
@@ -1053,10 +1064,12 @@ int main() {
 		return 1;
 	}
 	buildsysdict();
+	vm.mprotectsz = 0;
 	vm.PC = find("(abort)");
 	while (vm.PC < MEMSZ) oprun1();
 	if (fp) fclose(fp);
 	if (vm.PC > MEMSZ) {
+		DBG();
 		fprintf(stderr, "Dumping memory to memdump.\n");
 		FILE *fp = fopen("memdump", "w");
 		fwrite(vm.mem, MEMSZ, 1, fp);