Clamp BIOS io attempts to < 2 ^28 - 1 sectors (a.k.a. 128GB for

512-byte sectors) as some BIOSen get confused when we ask for sectors
higher up.

Uss u_int throughout the boot code to calculate sector addresses,
since 32 bits is enough to do 28  ^ 1 - 1 arithmetic. Add checks
for wraparound.

I can now install and boot from the 7th extended partition below
128GB.

Much feedback & guidance from deraadt@. Also from weingart@ on
BIOS io.

ok deraadt@ (less a couple of minor tweaks found in testing)

8 files changed, 123 insertions, 97 deletions

diff --git a/sys/arch/amd64/include/biosvar.h b/sys/arch/amd64/include/biosvar.h
index ba13e9fafa5..0abc8c2b4f8 100644
--- a/sys/arch/amd64/include/biosvar.h
+++ b/sys/arch/amd64/include/biosvar.h
@@ -1,5 +1,5 @@
 /* XXX - DSR */
-/*	$OpenBSD: biosvar.h,v 1.11 2010/11/22 21:07:18 miod Exp $	*/
+/*	$OpenBSD: biosvar.h,v 1.12 2011/03/14 22:14:40 krw Exp $	*/
 
 /*
  * Copyright (c) 1997-1999 Michael Shalayeff
@@ -36,6 +36,7 @@
 #define	BOOTARG_OFF	(NBPG*2)
 #define	BOOTARG_LEN	(NBPG*1)
 #define	BOOTBIOS_ADDR	(0x7c00)
+#define	BOOTBIOS_MAXSEC	((1 << 28) - 1)
 
 	/* BIOS configure flags */
 #define	BIOSF_BIOS32	0x0001
diff --git a/sys/arch/amd64/stand/installboot/installboot.c b/sys/arch/amd64/stand/installboot/installboot.c
index 75142e8bd90..0f736b85d37 100644
--- a/sys/arch/amd64/stand/installboot/installboot.c
+++ b/sys/arch/amd64/stand/installboot/installboot.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: installboot.c,v 1.15 2011/03/13 00:13:52 deraadt Exp $	*/
+/*	$OpenBSD: installboot.c,v 1.16 2011/03/14 22:14:40 krw Exp $	*/
 /*	$NetBSD: installboot.c,v 1.5 1995/11/17 23:23:50 gwr Exp $ */
 
 /*
@@ -107,14 +107,14 @@ static void	devread(int, void *, daddr64_t, size_t, char *);
 static void	sym_set_value(struct sym_data *, char *, u_int32_t);
 static void	pbr_set_symbols(char *, char *, struct sym_data *);
 static void	usage(void);
-static daddr64_t findopenbsd(int, struct disklabel *, daddr64_t, int *);
+static u_int	findopenbsd(int, struct disklabel *, u_int, int *);
 static void	write_bootblocks(int devfd, struct disklabel *);
 
 static int	sr_volume(int, int *, int *);
 static void	sr_installboot(int);
 static void	sr_installpbr(int, int, int);
 
-static daddr64_t mbr_eoff; /* Offset of the MBR extended partition. */
+static u_int	mbr_eoff; /* Offset of the MBR extended partition. */
 
 static void
 usage(void)
@@ -217,7 +217,7 @@ void
 write_bootblocks(int devfd, struct disklabel *dl)
 {
 	struct		stat sb;
-	daddr64_t	start = 0;
+	u_int		start = 0;
 	int		n = 8;
 
 	/* Write patched proto bootblock(s) into the superblock. */
@@ -238,15 +238,14 @@ write_bootblocks(int devfd, struct disklabel *dl)
 	if (dl->d_type != 0 && dl->d_type != DTYPE_FLOPPY &&
 	    dl->d_type != DTYPE_VND) {
 		/* Find OpenBSD partition. */
-		mbr_eoff = 0;	/* Offset of MBR extended partition. */
-		start = findopenbsd(devfd, dl, (daddr64_t)DOSBBSECTOR, &n);
-		if (start == -1)
+		mbr_eoff = DOSBBSECTOR;	/* Offset of MBR extended partition. */
+		start = findopenbsd(devfd, dl, DOSBBSECTOR, &n);
+		if (start == (u_int)-1)
  			errx(1, "no OpenBSD partition");
 	}
 
 	if (verbose)
-		fprintf(stderr, "/boot will be written at sector %lld\n",
-		    (long long)start);
+		fprintf(stderr, "/boot will be written at sector %u\n", start);
 
 	if (!nowrite) {
 		if (lseek(devfd, (off_t)start * dl->d_secsize, SEEK_SET) < 0 ||
@@ -255,12 +254,12 @@ write_bootblocks(int devfd, struct disklabel *dl)
 	}
 }
 
-daddr64_t
-findopenbsd(int devfd, struct disklabel *dl, daddr64_t mbroff, int *n)
+u_int
+findopenbsd(int devfd, struct disklabel *dl, u_int mbroff, int *n)
 {
 	struct		dos_mbr mbr;
 	struct		dos_partition *dp;
-	daddr64_t	start = -1;
+	u_int		start = (u_int)-1;
 	int		i;
 
 	/* Limit the number of recursions */
@@ -268,18 +267,17 @@ findopenbsd(int devfd, struct disklabel *dl, daddr64_t mbroff, int *n)
 		return (-1);
 
 	if (verbose)
-		fprintf(stderr, "%s boot record (%cBR) at sector %lld\n",
-		    (mbroff == (off_t)DOSBBSECTOR) ? "master" : "extended",
-		    (mbroff == (off_t)DOSBBSECTOR) ? 'M' : 'E',
-		    (long long)mbroff);
+		fprintf(stderr, "%s boot record (%cBR) at sector %u\n",
+		    (mbroff == DOSBBSECTOR) ? "master" : "extended",
+		    (mbroff == DOSBBSECTOR) ? 'M' : 'E', mbroff);
 
 	if (lseek(devfd, (off_t)mbroff * dl->d_secsize, SEEK_SET) < 0 ||
 	    read(devfd, &mbr, sizeof(mbr)) != sizeof(mbr))
 		err(4, "can't read boot record");
 
 	if (mbr.dmbr_sign != DOSMBR_SIGNATURE)
-		errx(1, "invalid boot record signature (0x%04X)",
-		    mbr.dmbr_sign);
+		errx(1, "invalid boot record signature (0x%04X) @ sector %u",
+		    mbr.dmbr_sign, mbroff);
 
 	for (i = 0; i < NDOSPART; i++) {
 		dp = &mbr.dmbr_parts[i];
@@ -288,21 +286,25 @@ findopenbsd(int devfd, struct disklabel *dl, daddr64_t mbroff, int *n)
 
 		if (verbose)
 			fprintf(stderr,
-			    "\tpartition %d: type 0x%02X offset %d size %d\n",
+			    "\tpartition %d: type 0x%02X offset %u size %u\n",
 			    i, dp->dp_typ, dp->dp_start, dp->dp_size);
 
 		if (dp->dp_typ == DOSPTYP_OPENBSD) {
-			start = (daddr64_t)dp->dp_start + mbroff;
+			if (dp->dp_start > (dp->dp_start + mbroff))
+				continue;
+			start = dp->dp_start + mbroff;
 			break;
 		}
 
 		if (dp->dp_typ == DOSPTYP_EXTEND ||
 		    dp->dp_typ == DOSPTYP_EXTENDL) {
-			mbroff = (daddr64_t)dp->dp_start + mbr_eoff;
-			if (!mbr_eoff)
-				mbr_eoff = (daddr64_t)dp->dp_start;
+			mbroff = dp->dp_start + mbr_eoff;
+			if (mbr_eoff == DOSBBSECTOR)
+				mbr_eoff = dp->dp_start;
+			if (mbroff < dp->dp_start)
+				continue;
 			start = findopenbsd(devfd, dl, mbroff, n);
-			if (start != -1)
+			if (start != (u_int)-1)
 				break;
 		}
 	}
diff --git a/sys/arch/amd64/stand/libsa/biosdev.c b/sys/arch/amd64/stand/libsa/biosdev.c
index c44c84da20b..b389d1adc69 100644
--- a/sys/arch/amd64/stand/libsa/biosdev.c
+++ b/sys/arch/amd64/stand/libsa/biosdev.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: biosdev.c,v 1.12 2011/03/13 00:13:52 deraadt Exp $	*/
+/*	$OpenBSD: biosdev.c,v 1.13 2011/03/14 22:14:40 krw Exp $	*/
 
 /*
  * Copyright (c) 1996 Michael Shalayeff
@@ -43,15 +43,14 @@ static const char *biosdisk_err(u_int);
 static int biosdisk_errno(u_int);
 
 int CHS_rw (int, int, int, int, int, int, void *);
-static int EDD_rw (int, int, u_int64_t, u_int32_t, void *);
+static int EDD_rw (int, int, u_int32_t, u_int32_t, void *);
 
-static daddr64_t findopenbsd(bios_diskinfo_t *, daddr64_t, const char **,
-    int *);
+static u_int findopenbsd(bios_diskinfo_t *, u_int, const char **, int *);
 
 extern int debug;
 int bios_bootdev;
 int bios_cddev = -1;		/* Set by srt0 if coming from CD */
-daddr64_t mbr_eoff;		/* Offset of the MBR extended partition. */
+u_int mbr_eoff;			/* Offset of MBR extended partition. */
 
 #if 0
 struct biosdisk {
@@ -211,11 +210,15 @@ CHS_rw(int rw, int dev, int cyl, int head, int sect, int nsect, void *buf)
 }
 
 static __inline int
-EDD_rw(int rw, int dev, u_int64_t daddr, u_int32_t nblk, void *buf)
+EDD_rw(int rw, int dev, u_int32_t daddr, u_int32_t nblk, void *buf)
 {
 	int rv;
 	volatile static struct EDD_CB cb;
 
+	/* Some (most?) BIOSen get confused by i/o above 2 ^ 28 - 1 sector. */
+	if ((daddr + nblk) > BOOTBIOS_MAXSEC)
+		return (1); /* Invalid function/parameter. */
+
 	/* Zero out reserved stuff */
 	cb.edd_res1 = 0;
 	cb.edd_res2 = 0;
@@ -243,7 +246,7 @@ EDD_rw(int rw, int dev, u_int64_t daddr, u_int32_t nblk, void *buf)
  * Read given sector, handling retry/errors/etc.
  */
 int
-biosd_io(int rw, bios_diskinfo_t *bd, daddr32_t off, int nsect, void *buf)
+biosd_io(int rw, bios_diskinfo_t *bd, u_int off, int nsect, void *buf)
 {
 	int dev = bd->bios_number;
 	int j, error;
@@ -343,12 +346,12 @@ biosd_io(int rw, bios_diskinfo_t *bd, daddr32_t off, int nsect, void *buf)
 /*
  * Try to read the bsd label on the given BIOS device
  */
-static daddr64_t
-findopenbsd(bios_diskinfo_t *bd, daddr64_t mbroff, const char **err, int *n)
+static u_int
+findopenbsd(bios_diskinfo_t *bd, u_int mbroff, const char **err, int *n)
 {
 	struct dos_mbr mbr;
 	struct dos_partition *dp;
-	daddr64_t start = -1;
+	u_int start = (u_int)-1;
 	int error, i;
 
 	/* Limit the number of recursions */
@@ -385,17 +388,21 @@ findopenbsd(bios_diskinfo_t *bd, daddr64_t mbroff, const char **err, int *n)
 			    dp->dp_start, dp->dp_start);
 #endif
 		if (dp->dp_typ == DOSPTYP_OPENBSD) {
-			start = (daddr64_t)dp->dp_start + mbroff;
+			if (dp->dp_start > (dp->dp_start + mbroff))
+				continue;
+			start = dp->dp_start + mbroff;
 			break;
 		}
 
 		if (dp->dp_typ == DOSPTYP_EXTEND ||
 		    dp->dp_typ == DOSPTYP_EXTENDL) {
-			mbroff = (daddr64_t)dp->dp_start + mbr_eoff;
-			if (!mbr_eoff)
-				mbr_eoff = (daddr64_t)dp->dp_start;
+			mbroff = dp->dp_start + mbr_eoff;
+			if (mbr_eoff == DOSBBSECTOR)
+				mbr_eoff = dp->dp_start;
+			if (mbroff < dp->dp_start)
+				continue;
 			start = findopenbsd(bd, mbroff, err, n);
-			if (start != -1)
+			if (start != (u_int)-1)
 				break;
 		}
 	}
@@ -406,7 +413,7 @@ findopenbsd(bios_diskinfo_t *bd, daddr64_t mbroff, const char **err, int *n)
 const char *
 bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 {
-	daddr64_t start = 0;
+	u_int start = 0;
 	char *buf;
 	const char *err = NULL;
 	int error;
@@ -419,9 +426,9 @@ bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 
 	/* MBR is a harddisk thing */
 	if (bd->bios_number & 0x80) {
-		mbr_eoff = 0;
-		start = findopenbsd(bd, (daddr64_t)DOSBBSECTOR, &err, &n);
-		if (start == -1) {
+		mbr_eoff = DOSBBSECTOR;
+		start = findopenbsd(bd, DOSBBSECTOR, &err, &n);
+		if (start == (u_int)-1) {
 			if (err != NULL)
 				return (err);
  			return "no OpenBSD partition\n";
@@ -436,7 +443,7 @@ bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 		printf("loading disklabel @ %u\n", off);
 #endif
 	/* read disklabel */
-	error = biosd_io(F_READ, bd, (daddr32_t)start, 1, buf);
+	error = biosd_io(F_READ, bd, start, 1, buf);
 
 	if(error)
 		return("failed to read disklabel");
@@ -659,7 +666,10 @@ biosstrategy(void *devdata, int rw, daddr32_t blk, size_t size, void *buf,
 			d_partitions[B_PARTITION(dip->bsddev)].p_offset;
 
 	/* Read all, sub-functions handle track boundaries */
-	error = biosd_io(rw, bd, blk, nsect, buf);
+	if (blk < 0)
+		error = EINVAL;
+	else
+		error = biosd_io(rw, bd, blk, nsect, buf);
 
 #ifdef BIOS_DEBUG
 	if (debug) {
diff --git a/sys/arch/amd64/stand/libsa/biosdev.h b/sys/arch/amd64/stand/libsa/biosdev.h
index 765ba0d0e59..fc0a0ce69ea 100644
--- a/sys/arch/amd64/stand/libsa/biosdev.h
+++ b/sys/arch/amd64/stand/libsa/biosdev.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: biosdev.h,v 1.3 2011/03/13 00:13:52 deraadt Exp $	*/
+/*	$OpenBSD: biosdev.h,v 1.4 2011/03/14 22:14:40 krw Exp $	*/
 
 /*
  * Copyright (c) 1996 Michael Shalayeff
@@ -49,7 +49,7 @@ int biosopen(struct open_file *, ...);
 int biosclose(struct open_file *);
 int biosioctl(struct open_file *, u_long, void *);
 int bios_getdiskinfo(int, bios_diskinfo_t *);
-int biosd_io(int, bios_diskinfo_t *, daddr32_t, int, void *);
+int biosd_io(int, bios_diskinfo_t *, u_int, int, void *);
 const char * bios_getdisklabel(bios_diskinfo_t *, struct disklabel *);
 
 /* diskprobe.c */
diff --git a/sys/arch/i386/include/biosvar.h b/sys/arch/i386/include/biosvar.h
index fff38e62b79..a044490736d 100644
--- a/sys/arch/i386/include/biosvar.h
+++ b/sys/arch/i386/include/biosvar.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: biosvar.h,v 1.53 2010/11/22 21:08:08 miod Exp $	*/
+/*	$OpenBSD: biosvar.h,v 1.54 2011/03/14 22:14:40 krw Exp $	*/
 
 /*
  * Copyright (c) 1997-1999 Michael Shalayeff
@@ -33,6 +33,7 @@
 #define	BOOTARG_OFF	(NBPG*2)
 #define	BOOTARG_LEN	(NBPG*1)
 #define	BOOTBIOS_ADDR	(0x7c00)
+#define	BOOTBIOS_MAXSEC	((1 << 28) - 1)
 
 	/* physical page for ptp 0 need for various tramps */
 #define PTP0_PA		(NBPG*3)	
diff --git a/sys/arch/i386/stand/installboot/installboot.c b/sys/arch/i386/stand/installboot/installboot.c
index 7cd28b2a078..be384a635e8 100644
--- a/sys/arch/i386/stand/installboot/installboot.c
+++ b/sys/arch/i386/stand/installboot/installboot.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: installboot.c,v 1.58 2011/03/13 00:13:52 deraadt Exp $	*/
+/*	$OpenBSD: installboot.c,v 1.59 2011/03/14 22:14:40 krw Exp $	*/
 /*	$NetBSD: installboot.c,v 1.5 1995/11/17 23:23:50 gwr Exp $ */
 
 /*
@@ -103,14 +103,14 @@ static void	devread(int, void *, daddr64_t, size_t, char *);
 static void	sym_set_value(struct sym_data *, char *, u_int32_t);
 static void	pbr_set_symbols(char *, char *, struct sym_data *);
 static void	usage(void);
-static daddr64_t findopenbsd(int, struct disklabel *, daddr64_t, int *);
+static u_int	findopenbsd(int, struct disklabel *, u_int, int *);
 static void	write_bootblocks(int devfd, struct disklabel *);
 
 static int	sr_volume(int, int *, int *);
 static void	sr_installboot(int);
 static void	sr_installpbr(int, int, int);
 
-static daddr64_t mbr_eoff; /* Offset of the MBR extended partition. */
+static u_int	mbr_eoff; /* Offset of the MBR extended partition. */
 
 static void
 usage(void)
@@ -213,7 +213,7 @@ void
 write_bootblocks(int devfd, struct disklabel *dl)
 {
 	struct		stat sb;
-	daddr64_t	start = 0;
+	u_int		start = 0;
 	int		n = 8;
 
 	/* Write patched proto bootblock(s) into the superblock. */
@@ -234,15 +234,14 @@ write_bootblocks(int devfd, struct disklabel *dl)
 	if (dl->d_type != 0 && dl->d_type != DTYPE_FLOPPY &&
 	    dl->d_type != DTYPE_VND) {
 		/* Find OpenBSD partition. */
-		mbr_eoff = 0;	/* Offset of MBR extended partition. */
-		start = findopenbsd(devfd, dl, (daddr64_t)DOSBBSECTOR, &n);
-		if (start == -1)
+		mbr_eoff = DOSBBSECTOR;	/* Offset of MBR extended partition. */
+		start = findopenbsd(devfd, dl, DOSBBSECTOR, &n);
+		if (start == (u_int)-1)
  			errx(1, "no OpenBSD partition");
 	}
 
 	if (verbose)
-		fprintf(stderr, "/boot will be written at sector %lld\n",
-		    (long long)start);
+		fprintf(stderr, "/boot will be written at sector %u\n", start);
 
 	if (!nowrite) {
 		if (lseek(devfd, (off_t)start * dl->d_secsize, SEEK_SET) < 0 ||
@@ -251,12 +250,12 @@ write_bootblocks(int devfd, struct disklabel *dl)
 	}
 }
 
-daddr64_t
-findopenbsd(int devfd, struct disklabel *dl, daddr64_t mbroff, int *n)
+u_int
+findopenbsd(int devfd, struct disklabel *dl, u_int mbroff, int *n)
 {
 	struct		dos_mbr mbr;
 	struct		dos_partition *dp;
-	daddr64_t	start = -1;
+	u_int		start = (u_int)-1;
 	int		i;
 
 	/* Limit the number of recursions */
@@ -264,18 +263,17 @@ findopenbsd(int devfd, struct disklabel *dl, daddr64_t mbroff, int *n)
 		return (-1);
 
 	if (verbose)
-		fprintf(stderr, "%s boot record (%cBR) at sector %lld\n",
-		    (mbroff == (off_t)DOSBBSECTOR) ? "master" : "extended",
-		    (mbroff == (off_t)DOSBBSECTOR) ? 'M' : 'E',
-		    (long long)mbroff);
+		fprintf(stderr, "%s boot record (%cBR) at sector %u\n",
+		    (mbroff == DOSBBSECTOR) ? "master" : "extended",
+		    (mbroff == DOSBBSECTOR) ? 'M' : 'E', mbroff);
 
-	if (lseek(devfd, mbroff * dl->d_secsize, SEEK_SET) < 0 ||
+	if (lseek(devfd, (off_t)mbroff * dl->d_secsize, SEEK_SET) < 0 ||
 	    read(devfd, &mbr, sizeof(mbr)) != sizeof(mbr))
 		err(4, "can't read boot record");
 
 	if (mbr.dmbr_sign != DOSMBR_SIGNATURE)
-		errx(1, "invalid boot record signature (0x%04X) @ sector %lld",
-		    mbr.dmbr_sign, (long long)mbroff);
+		errx(1, "invalid boot record signature (0x%04X) @ sector %u",
+		    mbr.dmbr_sign, mbroff);
 
 	for (i = 0; i < NDOSPART; i++) {
 		dp = &mbr.dmbr_parts[i];
@@ -284,21 +282,25 @@ findopenbsd(int devfd, struct disklabel *dl, daddr64_t mbroff, int *n)
 
 		if (verbose)
 			fprintf(stderr,
-			    "\tpartition %d: type 0x%02X offset %d size %d\n",
+			    "\tpartition %d: type 0x%02X offset %u size %u\n",
 			    i, dp->dp_typ, dp->dp_start, dp->dp_size);
 
 		if (dp->dp_typ == DOSPTYP_OPENBSD) {
-			start = (daddr64_t)dp->dp_start + mbroff;
+			if (dp->dp_start > (dp->dp_start + mbroff))
+				continue;
+			start = dp->dp_start + mbroff;
 			break;
 		}
 
 		if (dp->dp_typ == DOSPTYP_EXTEND ||
 		    dp->dp_typ == DOSPTYP_EXTENDL) {
-			mbroff = (daddr64_t)dp->dp_start + mbr_eoff;
-			if (!mbr_eoff)
-				mbr_eoff = (daddr64_t)dp->dp_start;
+			mbroff = dp->dp_start + mbr_eoff;
+			if (mbr_eoff == DOSBBSECTOR)
+				mbr_eoff = dp->dp_start;
+			if (mbroff < dp->dp_start)
+				continue;
 			start = findopenbsd(devfd, dl, mbroff, n);
-			if (start != -1)
+			if (start != (u_int)-1)
 				break;
 		}
 	}
diff --git a/sys/arch/i386/stand/libsa/biosdev.c b/sys/arch/i386/stand/libsa/biosdev.c
index 385b0cc2b90..fe2820e2243 100644
--- a/sys/arch/i386/stand/libsa/biosdev.c
+++ b/sys/arch/i386/stand/libsa/biosdev.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: biosdev.c,v 1.80 2011/03/13 00:13:53 deraadt Exp $	*/
+/*	$OpenBSD: biosdev.c,v 1.81 2011/03/14 22:14:40 krw Exp $	*/
 
 /*
  * Copyright (c) 1996 Michael Shalayeff
@@ -44,15 +44,14 @@ static const char *biosdisk_err(u_int);
 static int biosdisk_errno(u_int);
 
 int CHS_rw (int, int, int, int, int, int, void *);
-static int EDD_rw (int, int, u_int64_t, u_int32_t, void *);
+static int EDD_rw (int, int, u_int32_t, u_int32_t, void *);
 
-static daddr64_t findopenbsd(bios_diskinfo_t *, daddr64_t, const char **,
-    int *);
+static u_int findopenbsd(bios_diskinfo_t *, u_int, const char **, int *);
 
 extern int debug;
 int bios_bootdev;
 int bios_cddev = -1;		/* Set by srt0 if coming from CD */
-daddr64_t mbr_eoff;		/* Offset of MBR extended partition. */
+u_int mbr_eoff;			/* Offset of MBR extended partition. */
 
 #if 0
 struct biosdisk {
@@ -214,11 +213,15 @@ CHS_rw(int rw, int dev, int cyl, int head, int sect, int nsect, void *buf)
 }
 
 static __inline int
-EDD_rw(int rw, int dev, u_int64_t daddr, u_int32_t nblk, void *buf)
+EDD_rw(int rw, int dev, u_int32_t daddr, u_int32_t nblk, void *buf)
 {
 	int rv;
 	volatile static struct EDD_CB cb;
 
+	/* Some (most?) BIOSen get confused by i/o above 2 ^ 28 - 1 sector. */
+	if ((daddr + nblk) > BOOTBIOS_MAXSEC)
+		return (1); /* Invalid function/parameter. */
+
 	/* Zero out reserved stuff */
 	cb.edd_res1 = 0;
 	cb.edd_res2 = 0;
@@ -246,7 +249,7 @@ EDD_rw(int rw, int dev, u_int64_t daddr, u_int32_t nblk, void *buf)
  * Read given sector, handling retry/errors/etc.
  */
 int
-biosd_io(int rw, bios_diskinfo_t *bd, daddr32_t off, int nsect, void *buf)
+biosd_io(int rw, bios_diskinfo_t *bd, u_int off, int nsect, void *buf)
 {
 	int dev = bd->bios_number;
 	int j, error;
@@ -346,12 +349,12 @@ biosd_io(int rw, bios_diskinfo_t *bd, daddr32_t off, int nsect, void *buf)
 /*
  * Try to read the bsd label on the given BIOS device
  */
-static daddr64_t
-findopenbsd(bios_diskinfo_t *bd, daddr64_t mbroff, const char **err, int *n)
+static u_int
+findopenbsd(bios_diskinfo_t *bd, u_int mbroff, const char **err, int *n)
 {
 	struct dos_mbr mbr;
 	struct dos_partition *dp;
-	daddr64_t start = -1; 
+	u_int start = (u_int)-1; 
 	int error, i;
 
 	/* Limit the number of recursions */
@@ -388,17 +391,21 @@ findopenbsd(bios_diskinfo_t *bd, daddr64_t mbroff, const char **err, int *n)
 			    dp->dp_start, dp->dp_start);
 #endif
 		if (dp->dp_typ == DOSPTYP_OPENBSD) {
-			start = (daddr64_t)dp->dp_start + mbroff;
+			if (dp->dp_start > (dp->dp_start + mbroff))
+				continue;
+			start = dp->dp_start + mbroff;
 			break;
 		}
 
 		if (dp->dp_typ == DOSPTYP_EXTEND ||
 		    dp->dp_typ == DOSPTYP_EXTENDL) {
-			mbroff = (daddr64_t)dp->dp_start + mbr_eoff;
-			if (!mbr_eoff)
-				mbr_eoff = (daddr64_t)dp->dp_start;
+			mbroff = dp->dp_start + mbr_eoff;
+			if (mbr_eoff == DOSBBSECTOR)
+				mbr_eoff = dp->dp_start;
+			if (mbroff < dp->dp_start)
+				continue;
 			start = findopenbsd(bd, mbroff, err, n);
-			if (start != -1)
+			if (start != (u_int)-1)
 				break;	
 		}
 	}
@@ -409,7 +416,7 @@ findopenbsd(bios_diskinfo_t *bd, daddr64_t mbroff, const char **err, int *n)
 const char *
 bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 {
-	daddr64_t start = 0;
+	u_int start = 0;
 	char *buf;
 	const char *err = NULL;
 	int error;
@@ -422,9 +429,9 @@ bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 
 	/* MBR is a harddisk thing */
 	if (bd->bios_number & 0x80) {
-		mbr_eoff = 0;
-		start = findopenbsd(bd, (daddr64_t)DOSBBSECTOR, &err, &n);
-		if (start == -1) {
+		mbr_eoff = DOSBBSECTOR;
+		start = findopenbsd(bd, DOSBBSECTOR, &err, &n);
+		if (start == (u_int)-1) {
 			if (err != NULL)
 				return (err);
  			return "no OpenBSD partition\n";
@@ -439,7 +446,7 @@ bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 		printf("loading disklabel @ %lld\n", start);
 #endif
 	/* read disklabel */
-	error = biosd_io(F_READ, bd, (daddr32_t)start, 1, buf);
+	error = biosd_io(F_READ, bd, start, 1, buf);
 
 	if (error)
 		return "failed to read disklabel";
@@ -662,7 +669,10 @@ biosstrategy(void *devdata, int rw, daddr32_t blk, size_t size, void *buf,
 			d_partitions[B_PARTITION(dip->bsddev)].p_offset;
 
 	/* Read all, sub-functions handle track boundaries */
-	error = biosd_io(rw, bd, blk, nsect, buf);
+	if (blk < 0)
+		error = EINVAL;
+	else
+		error = biosd_io(rw, bd, blk, nsect, buf);
 
 #ifdef BIOS_DEBUG
 	if (debug) {
diff --git a/sys/arch/i386/stand/libsa/biosdev.h b/sys/arch/i386/stand/libsa/biosdev.h
index 88463c927f9..3cd99d18217 100644
--- a/sys/arch/i386/stand/libsa/biosdev.h
+++ b/sys/arch/i386/stand/libsa/biosdev.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: biosdev.h,v 1.32 2011/03/13 00:13:53 deraadt Exp $	*/
+/*	$OpenBSD: biosdev.h,v 1.33 2011/03/14 22:14:40 krw Exp $	*/
 
 /*
  * Copyright (c) 1996 Michael Shalayeff
@@ -49,7 +49,7 @@ int biosopen(struct open_file *, ...);
 int biosclose(struct open_file *);
 int biosioctl(struct open_file *, u_long, void *);
 int bios_getdiskinfo(int, bios_diskinfo_t *);
-int biosd_io(int, bios_diskinfo_t *, daddr32_t, int, void *);
+int biosd_io(int, bios_diskinfo_t *, u_int, int, void *);
 const char * bios_getdisklabel(bios_diskinfo_t *, struct disklabel *);
 
 /* diskprobe.c */