nooc

commit 2637645b18ff9ca6c87f1f2c33771014dac50483
parent dacb5b542397620ba34790d08a3975ad3561a3a9
Author: Nihal Jere <nihal@nihaljere.xyz>
Date:   Wed,  3 Nov 2021 14:39:23 -0500

can do arbitrary syscalls

Diffstat:
A
array.c
 | 
21
+++++++++++++++++++++
A
array.h
 | 
4
++++
M
main.c
 | 
76
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------
M
prog.nc
 | 
4
++--

4 files changed, 90 insertions(+), 15 deletions(-)
diff --git a/array.c b/array.c
@@ -0,0 +1,21 @@
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "array.h"
+
+int
+_array_add(void **data, size_t size, size_t *len, size_t *cap, void *new)
+{
+	if (*len == *cap) {
+		*cap = *cap ? 2*(*cap)*size : 1;
+		*data = realloc(*data, size*(*cap));
+		if (*data == NULL)
+			return -1;
+	}
+
+	memcpy(*data + size*(*len), new, size);
+	*len += 1;
+
+	return *len;
+}
diff --git a/array.h b/array.h
@@ -0,0 +1,4 @@
+#define array_add(arr, new) \
+	_array_add((void **) &(arr->data), sizeof(new), &(arr->len), &(arr->cap), &new);
+
+int _array_add(void **data, size_t size, size_t *len, size_t *cap, void *new);
diff --git a/main.c b/main.c
@@ -8,6 +8,8 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+#include "array.h"
+
 char code[] = {0xb8, 0, 0x00, 0x00, 0x00, 0xbf, 0x00, 0x00, 0x00, 0x00, 0xf, 0x5};
 
 int
@@ -156,9 +158,15 @@ enum func {
 	FUNC_EXIT
 };
 
+struct fparams {
+	size_t cap;
+	size_t len;
+	int *data;
+};
+
 struct fcall {
 	enum func func;
-	int val;
+	struct fparams params;
 };
 
 void
@@ -180,27 +188,62 @@ expect(struct token *tok, enum tokentype type)
 struct fcall
 parse(struct token *tok)
 {
-	struct fcall fcall;
+	struct fcall fcall = { 0 };
 	expect(tok, TOK_SYSCALL);
 	tok = tok->next;
 	expect(tok, TOK_LPAREN);
 	tok = tok->next;
 
-	expect(tok, TOK_EXIT);
-	fcall.func = FUNC_EXIT;
-	tok = tok->next;
-	expect(tok, TOK_COMMA);
-	tok = tok->next;
-	expect(tok, TOK_NUM);
+	int val;
+	while (1) {
+		expect(tok, TOK_NUM);
+		val = strtol(tok->slice.ptr, NULL, 10);
+		array_add((&fcall.params), val);
+		tok = tok->next;
+
+		if (tok->type == TOK_RPAREN)
+			break;
+		expect(tok, TOK_COMMA);
+		tok = tok->next;
+	}
 
 	// FIXME: error check
-	fcall.val = strtol(tok->slice.ptr, NULL, 10);
-	tok = tok->next;
 	expect(tok, TOK_RPAREN);
 	tok = tok->next;
 	return fcall;
 }
 
+size_t
+gensyscall(char *buf, struct fparams *params)
+{
+	if (params->len > 7)
+		error("syscall can take at most 7 parameters");
+
+	if (buf) {
+		char *ptr = buf;
+		char mov[] = {0x48, 0xc7};
+		char padding[] = {0, 0, 0};
+
+		// encoding for argument registers in ABI order
+		char regs[] = {0, 7, 6, 2, 10, 8, 9};
+		for (int i = 0; i < params->len; i++) {
+			memcpy(ptr, mov, 2);
+			ptr += 2;
+			char op1 = 0xc0 | regs[i];
+			*(ptr++) = op1;
+			*(ptr++) = params->data[i];
+			memset(ptr, 0, 3);
+			ptr += 3;
+		}
+
+		char syscall[] = {0x0f, 0x05};
+		memcpy(ptr, syscall, 2);
+	}
+
+	// for now, we assume each mov is 7 bytes encoded, and 2 bytes for syscall
+	return 7*params->len + 2;
+}
+
 struct stat statbuf;
 
 int
@@ -232,7 +275,7 @@ main(int argc, char *argv[])
 	switch (fcall.func) {
 	case FUNC_EXIT:
 		code[1] = 60;
-		code[6] = fcall.val;
+		code[6] = fcall.params.data[0];
 	}
 
 	FILE *out = fopen(argv[2], "w");
@@ -242,8 +285,15 @@ main(int argc, char *argv[])
 		return 1;
 	}
 
-	elf(code, sizeof(code), out);
-	fprintf(stderr, "size: %d\n", sizeof(code));
+	size_t len = gensyscall(NULL, &(fcall.params));
+	char *fcode = malloc(len);
+	if (!fcode)
+		error("gensyscall malloc failed");
+
+	gensyscall(fcode, &(fcall.params));
+
+	elf(fcode, len, out);
+	fprintf(stderr, "size: %d\n", len);
 
 	fclose(out);
 }
diff --git a/prog.nc b/prog.nc
@@ -1 +1 @@
-syscall(exit, 12)-
\ No newline at end of file
+syscall(60, 12)+
\ No newline at end of file