Date: Sun, 17 Mar 2002 19:04:43 +0100 (CET) From: Thomas Quinot <thomas@cuivre.fr.eu.org> To: FreeBSD-gnats-submit@FreeBSD.org Subject: i386/36015: [patch] boot2.c deobfuscation Message-ID: <20020317180443.6A9D42C3D1@melusine.cuivre.fr.eu.org>
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>Number: 36015
>Category: i386
>Synopsis: [patch] boot2.c deobfuscation
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Sun Mar 17 10:10:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Thomas Quinot
>Release: FreeBSD 4.5-STABLE i386
>Organization:
>Environment:
System: FreeBSD melusine.cuivre.fr.eu.org 4.5-STABLE FreeBSD 4.5-STABLE #1: Thu Jan 31 22:48:26 CET 2002 thomas@melusine.cuivre.fr.eu.org:/usr2/obj/usr2/src/sys/MELUSINE i386
>Description:
The code in boot2.c is rather obscure.
>How-To-Repeat:
Look at the sources.
>Fix:
The following patches clarifies the stream of control at
the beginning of main() by making autoboot a two-state
variable (instead of a 3-state), with no functional at all.
Magical numeric values for ioctrl are replaced with #define'd
macros.
Hard-coded tick values for calls to keyhit are replaced
by static expressions in terms of multiples of a SECOND
#define. This change introduces a functional difference:
the first time-out will be 1 tick shorter.
Index: sys/boot/i386/boot2/boot2.c
===================================================================
RCS file: /home/ncvs/src/sys/boot/i386/boot2/boot2.c,v
retrieving revision 1.37
diff -u -r1.37 boot2.c
--- sys/boot/i386/boot2/boot2.c 13 Mar 2002 11:03:36 -0000 1.37
+++ sys/boot/i386/boot2/boot2.c 15 Mar 2002 12:46:54 -0000
@@ -37,6 +37,11 @@
#include "boot2.h"
#include "lib.h"
+#define IO_KEYBOARD 1
+#define IO_SERIAL 2
+
+#define SECOND 18 /* Circa that many ticks in a second. */
+
#define RBX_ASKNAME 0x0 /* -a */
#define RBX_SINGLE 0x1 /* -s */
#define RBX_DFLTROOT 0x5 /* -r */
@@ -136,7 +141,7 @@
static struct bootinfo bootinfo;
static int ls;
static uint32_t fs_off;
-static uint8_t ioctrl = 0x1;
+static uint8_t ioctrl = IO_KEYBOARD;
void exit(int);
static void load(const char *);
@@ -279,34 +284,39 @@
bootinfo.bi_memsizes_valid++;
for (i = 0; i < N_BIOS_GEOM; i++)
bootinfo.bi_bios_geom[i] = drvinfo(i);
- autoboot = 2;
+
+ /* Process configuration file */
+
+ autoboot = 1;
readfile(PATH_CONFIG, cmd, sizeof(cmd));
if (*cmd) {
printf("%s: %s", PATH_CONFIG, cmd);
if (parse(cmd))
autoboot = 0;
- *cmd = 0;
}
- if (autoboot && !*kname) {
- if (autoboot == 2) {
- memcpy(kname, PATH_BOOT3, sizeof(PATH_BOOT3));
- if (!keyhit(0x37)) {
- load(kname);
- autoboot = 1;
- }
- }
- if (autoboot == 1)
+
+ /* Try to exec stage 3 boot loader. If interrupted by a keypress, *
+ * or in case of failure, try to load a kernel directly instaed. */
+
+ if (autoboot) {
+ memcpy(kname, PATH_BOOT3, sizeof(PATH_BOOT3));
+ if (!keyhit(3 * SECOND)) {
+ load(kname);
memcpy(kname, PATH_KERNEL, sizeof(PATH_KERNEL));
+ }
}
+
+ /* Present the user with the boot2 prompt. */
+
for (;;) {
printf(" \n>> FreeBSD/i386 BOOT\n"
"Default: %u:%s(%u,%c)%s\n"
"boot: ",
dsk.drive & DRV_MASK, dev_nm[dsk.type], dsk.unit,
'a' + dsk.part, kname);
- if (ioctrl & 0x2)
+ if (ioctrl & IO_SERIAL)
sio_flush();
- if (!autoboot || keyhit(0x5a))
+ if (!autoboot || keyhit(5 * SECOND))
getstr(cmd, sizeof(cmd));
else
putchar('\n');
@@ -445,9 +455,9 @@
opts |= 1 << RBX_DUAL | 1 << RBX_SERIAL;
opts &= ~(1 << RBX_PROBEKBD);
}
- ioctrl = opts & 1 << RBX_DUAL ? 0x3 :
- opts & 1 << RBX_SERIAL ? 0x2 : 0x1;
- if (ioctrl & 0x2)
+ ioctrl = opts & 1 << RBX_DUAL ? (IO_SERIAL | IO_KEYBOARD) :
+ opts & 1 << RBX_SERIAL ? IO_SERIAL : IO_KEYBOARD;
+ if (ioctrl & IO_SERIAL)
sio_init();
} else {
for (q = arg--; *q && *q != '('; q++);
@@ -790,9 +800,9 @@
static int
xputc(int c)
{
- if (ioctrl & 0x1)
+ if (ioctrl & IO_KEYBOARD)
putc(c);
- if (ioctrl & 0x2)
+ if (ioctrl & IO_SERIAL)
sio_putc(c);
return c;
}
@@ -801,9 +811,9 @@
xgetc(int fn)
{
for (;;) {
- if (ioctrl & 0x1 && getc(1))
+ if (ioctrl & IO_KEYBOARD && getc(1))
return fn ? 1 : getc(0);
- if (ioctrl & 0x2 && sio_ischar())
+ if (ioctrl & IO_SERIAL && sio_ischar())
return fn ? 1 : sio_getc();
if (fn)
return 0;
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