prepcore: error out if the compressed image is too large to load

Export, from each loader stage, the symbol MaxLMA which indicates to
prepcore how big the image is allowed to be.  Change prepcore to
enforce this limit and to error out otherwise.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

7 files changed, 36 insertions, 16 deletions

diff --git a/core/common.inc b/core/common.inc
index ad64c23c..80dbb4f9 100644
--- a/core/common.inc
+++ b/core/common.inc
@@ -18,3 +18,7 @@
 %include "strcpy.inc"           ; strcpy()
 %include "idle.inc"		; Idle handling
 %include "adv.inc"		; Auxillary Data Vector
+
+; Note: the prefix section is included late, to avoid problems with some
+; versions of NASM that had issues with forward references to EQU symbols.
+%include "prefix.inc"		; Prefix section for prepcore
diff --git a/core/diskstart.inc b/core/diskstart.inc
index b713a1ea..b8047264 100644
--- a/core/diskstart.inc
+++ b/core/diskstart.inc
@@ -668,8 +668,8 @@ rl_checkpt_off	equ ($-$$)
 
 ; Sector pointers
 		alignz 4
-		global MaxInitDataSize
 MaxInitDataSize	equ 96 << 10
+MaxLMA		equ 0x7c00+SECTOR_SIZE+MaxInitDataSize
 SectorPtrs	times MaxInitDataSize >> SECTOR_SHIFT dd 0
 SectorPtrsEnd	equ $
 
diff --git a/core/isolinux.asm b/core/isolinux.asm
index 37c14744..b2c9c986 100644
--- a/core/isolinux.asm
+++ b/core/isolinux.asm
@@ -431,6 +431,8 @@ found_file:
 		; address (7C00h) is *not* 2K-sector-aligned, the safest
 		; way to deal with this is to load into the xfer_buf_seg
 		; and then copy the data in place.
+MaxLMA		equ xfer_buf_seg << 4
+
 		mov bx,(7C00h+SECTOR_SIZE) >> 4
 		mov bp,[ImageSectors]
 
diff --git a/core/layout.inc b/core/layout.inc
index e2c7cbc5..fe292b14 100644
--- a/core/layout.inc
+++ b/core/layout.inc
@@ -134,18 +134,3 @@ pktbuf_seg	equ cache_seg		; PXELINUX packet buffers
 %endif
 
 comboot_seg	equ real_mode_seg	; COMBOOT image loading zone
-
-;
-; The prefix is a small structure that prefaces the actual code;
-; it gives the compression program necessary information.
-;
-
-		section .prefix		nowrite progbits align=16
-pfx_start	dd _start		; Start of raw chunk
-pfx_compressed	dd __pm_code_lma	; Start of compressed chunk
-pfx_cdatalen	dd lzo_data_size	; Pointer to compressed size field
-%if IS_ISOLINUX
-pfx_checksum	dd bi_length		; File length and checksum fields
-%else
-pfx_checksum	dd 0			; No checksum
-%endif
diff --git a/core/prefix.inc b/core/prefix.inc
new file mode 100644
index 00000000..9c8724b5
--- /dev/null
+++ b/core/prefix.inc
@@ -0,0 +1,17 @@
+;
+; The prefix is a small structure that prefaces the actual code;
+; it gives the compression program necessary information.
+;
+
+		section .prefix		nowrite progbits align=16
+pfx_start	dd _start		; Start of raw chunk
+pfx_compressed	dd __pm_code_lma	; Start of compressed chunk
+pfx_cdatalen	dd lzo_data_size	; Pointer to compressed size field
+%if IS_ISOLINUX
+pfx_checksum	dd bi_length		; File length and checksum fields
+%else
+pfx_checksum	dd 0			; No checksum
+%endif
+pfx_maxlma	dd MaxLMA		; Maximum size
+
+		section .text16
diff --git a/core/pxelinux.asm b/core/pxelinux.asm
index bb536a6c..b866369c 100644
--- a/core/pxelinux.asm
+++ b/core/pxelinux.asm
@@ -224,6 +224,10 @@ packet_buf_size	equ $-packet_buf
 StackBuf	equ $-44		; Base of stack if we use our own
 StackTop	equ StackBuf
 
+		; PXE loads the whole file, but assume it can't be more
+		; than (384-31)K in size.
+MaxLMA		equ 384*1024
+
 ;
 ; Primary entry point.
 ;
diff --git a/lzo/prepcore.c b/lzo/prepcore.c
index cb6b483a..fc1b6c6f 100644
--- a/lzo/prepcore.c
+++ b/lzo/prepcore.c
@@ -95,6 +95,7 @@ struct prefix {
     uint32_t pfx_compressed;
     uint32_t pfx_cdatalen;
     uint32_t pfx_checksum;
+    uint32_t pfx_maxlma;
 };
 
 static inline uint32_t get_32(const uint32_t * p)
@@ -317,6 +318,13 @@ int __lzo_cdecl_main main(int argc, char *argv[])
 	set_32((uint32_t *) (infile + soff + 4), csum);
     }
 
+    if (offset+outfile_len > get_32(&prefix->pfx_maxlma)) {
+	printf("%s: output too big (%lu, max %lu)\n",
+	       (unsigned long)offset+outfile_len,
+	       (unsigned long)get_32(&prefix->pfx_maxlma));
+	exit(1);
+    }
+
     f = fopen(out_name, "wb");
     if (f == NULL) {
 	printf("%s: cannot open output file %s\n", progname, out_name);