[PATCH v4 04/20] x86, boot: Move z_extract_offset calculation to header.S

[Baoquan He <bhe@redhat.com>]

From: Yinghai Lu <yinghai@kernel.org>

Current z_extract_offset is calculated in boot/compressed/mkpiggy.c. The
problem is in mkpiggy.c we don't know the detail of decompressor. Then
we just get a rough z_extract_offset according to extra_bytes. As we know
extra_bytes can only promise a safety margin when decompressing. In fact
this brings some risks:

 - output+output_len could be much bigger than input+input_len. In this
   cass decompressed kernel plus relocs could overwrite decompressing
   method code even when they are running.

 - ehead of ZO could be bigger than z_extract_offset. In this case overwrite
   could happen when head code is running to move ZO to end of buffer.
   Though currently the size of head code is very small it's still a
   potential risk. Because no rule to limit the size of head code of ZO,
   it has possibility to be very big.

Now move z_extract_offset calculation to header.S, and adjust z_extract_offset
to make sure that above two cases never happen.

Besides we have made ZO always be in the end of decompressing buffer,
z_extract_offset is only used here to calculate an appropriate INIT_SIZE,
no other place need it now. So no need to put it in voffset.h.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Baoquan He <bhe@redhat.com>
---
v2->v3:
    Tune the patch log.
    Remove code comment above init_size.
    I still think extra_bytes shoule be taken as below formula to cover
    the worst case of xz.
#define ZO_z_extra_bytes ((ZO_z_output_len >> 12) + 65536 + 128)

 arch/x86/boot/Makefile             |  2 +-
 arch/x86/boot/compressed/misc.c    |  5 +----
 arch/x86/boot/compressed/mkpiggy.c | 15 +--------------
 arch/x86/boot/header.S             | 22 +++++++++++++++++++++-
 4 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index bbe1a62..bd021e5 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -87,7 +87,7 @@ targets += voffset.h
 $(obj)/voffset.h: vmlinux FORCE
 	$(call if_changed,voffset)
 
-sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|_end\|z_.*\)$$/\#define ZO_\2 0x\1/p'
+sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|_end\|_ehead\|_text\|z_.*\)$$/\#define ZO_\2 0x\1/p'
 
 quiet_cmd_zoffset = ZOFFSET $@
       cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index c4477d5..e2a998f 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -83,13 +83,10 @@
  * To avoid problems with the compressed data's meta information an extra 18
  * bytes are needed.  Leading to the formula:
  *
- * extra_bytes = (uncompressed_size >> 12) + 32768 + 18 + decompressor_size.
+ * extra_bytes = (uncompressed_size >> 12) + 32768 + 18.
  *
  * Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
  * Adding 32768 instead of 32767 just makes for round numbers.
- * Adding the decompressor_size is necessary as it musht live after all
- * of the data as well.  Last I measured the decompressor is about 14K.
- * 10K of actual data and 4K of bss.
  *
  */
 
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index b980046..a613c84 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -21,8 +21,7 @@
  * ----------------------------------------------------------------------- */
 
 /*
- * Compute the desired load offset from a compressed program; outputs
- * a small assembly wrapper with the appropriate symbols defined.
+ * outputs a small assembly wrapper with the appropriate symbols defined.
  */
 
 #include <stdlib.h>
@@ -35,7 +34,6 @@ int main(int argc, char *argv[])
 {
 	uint32_t olen;
 	long ilen;
-	unsigned long offs;
 	unsigned long run_size;
 	FILE *f = NULL;
 	int retval = 1;
@@ -67,15 +65,6 @@ int main(int argc, char *argv[])
 	ilen = ftell(f);
 	olen = get_unaligned_le32(&olen);
 
-	/*
-	 * Now we have the input (compressed) and output (uncompressed)
-	 * sizes, compute the necessary decompression offset...
-	 */
-
-	offs = (olen > ilen) ? olen - ilen : 0;
-	offs += olen >> 12;	/* Add 8 bytes for each 32K block */
-	offs += 64*1024 + 128;	/* Add 64K + 128 bytes slack */
-	offs = (offs+4095) & ~4095; /* Round to a 4K boundary */
 	run_size = atoi(argv[2]);
 
 	printf(".section \".rodata..compressed\",\"a\",@progbits\n");
@@ -83,8 +72,6 @@ int main(int argc, char *argv[])
 	printf("z_input_len = %lu\n", ilen);
 	printf(".globl z_output_len\n");
 	printf("z_output_len = %lu\n", (unsigned long)olen);
-	printf(".globl z_extract_offset\n");
-	printf("z_extract_offset = 0x%lx\n", offs);
 	printf(".globl z_run_size\n");
 	printf("z_run_size = %lu\n", run_size);
 
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 6236b9e..1c057e3 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -440,7 +440,27 @@ setup_data:		.quad 0			# 64-bit physical pointer to
 
 pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
 
-#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_extract_offset)
+/* Check arch/x86/boot/compressed/misc.c for the formula of extra_bytes*/
+#define ZO_z_extra_bytes ((ZO_z_output_len >> 12) + 65536 + 128)
+#if ZO_z_output_len > ZO_z_input_len
+#define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - ZO_z_input_len)
+#else
+#define ZO_z_extract_offset ZO_z_extra_bytes
+#endif
+
+/*
+ * extract_offset has to be bigger than ZO head section. Otherwise
+ * during head code running to move ZO to end of buffer, it will
+ * overwrite head code itself.
+ */
+#if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset
+#define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095)
+#else
+#define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095)
+#endif
+
+#define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_min_extract_offset)
+
 #define VO_INIT_SIZE	(VO__end - VO__text)
 #if ZO_INIT_SIZE > VO_INIT_SIZE
 #define INIT_SIZE ZO_INIT_SIZE
-- 
2.5.0