x86/boot: Derive file size from _edata symbol

Tweak the linker script so that the value of _edata represents the
decompressor binary's file size rounded up to the appropriate alignment.
This removes the need to calculate it in the build tool, and will make
it easier to refer to the file size from the header directly in
subsequent changes to the PE header layout.

While adding _edata to the sed regex that parses the compressed
vmlinux's symbol list, tweak the regex a bit for conciseness.

This change has no impact on the resulting bzImage binary when
configured with CONFIG_EFI_STUB=y.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915171623.655440-14-ardb@google.com

4 files changed, 12 insertions, 25 deletions

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index 0e98bc503699..cc04917b1ac6 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -89,7 +89,7 @@ $(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE
 
 SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
 
-sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|efi32_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|z_.*\)$$/\#define ZO_\2 0x\1/p'
+sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_edata\|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/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 4ff6ab1b67d9..b688598db28e 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -47,6 +47,9 @@ SECTIONS
 		_data = . ;
 		*(.data)
 		*(.data.*)
+
+		/* Add 4 bytes of extra space for a CRC-32 checksum */
+		. = ALIGN(. + 4, 0x20);
 		_edata = . ;
 	}
 	. = ALIGN(L1_CACHE_BYTES);
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 06bd72a324c1..34e9b35b827c 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -233,7 +233,7 @@ sentinel:	.byte 0xff, 0xff        /* Used to detect broken loaders */
 hdr:
 		.byte setup_sects - 1
 root_flags:	.word ROOT_RDONLY
-syssize:	.long 0			/* Filled in by build.c */
+syssize:	.long ZO__edata / 16
 ram_size:	.word 0			/* Obsolete */
 vid_mode:	.word SVGA_MODE
 root_dev:	.word 0			/* Default to major/minor 0/0 */
diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index 745d64b6d930..e792c6c5a634 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -52,6 +52,7 @@ u8 buf[SETUP_SECT_MAX*512];
 
 static unsigned long efi_pe_entry;
 static unsigned long efi32_pe_entry;
+static unsigned long _edata;
 static unsigned long _end;
 
 /*----------------------------------------------------------------------*/
@@ -308,6 +309,7 @@ static void parse_zoffset(char *fname)
 	while (p && *p) {
 		PARSE_ZOFS(p, efi_pe_entry);
 		PARSE_ZOFS(p, efi32_pe_entry);
+		PARSE_ZOFS(p, _edata);
 		PARSE_ZOFS(p, _end);
 
 		p = strchr(p, '\n');
@@ -320,7 +322,6 @@ int main(int argc, char ** argv)
 {
 	unsigned int i, sz, setup_sectors;
 	int c;
-	u32 sys_size;
 	struct stat sb;
 	FILE *file, *dest;
 	int fd;
@@ -368,24 +369,14 @@ int main(int argc, char ** argv)
 		die("Unable to open `%s': %m", argv[2]);
 	if (fstat(fd, &sb))
 		die("Unable to stat `%s': %m", argv[2]);
-	sz = sb.st_size;
+	if (_edata != sb.st_size)
+		die("Unexpected file size `%s': %u != %u", argv[2], _edata,
+		    sb.st_size);
+	sz = _edata - 4;
 	kernel = mmap(NULL, sz, PROT_READ, MAP_SHARED, fd, 0);
 	if (kernel == MAP_FAILED)
 		die("Unable to mmap '%s': %m", argv[2]);
-	/* Number of 16-byte paragraphs, including space for a 4-byte CRC */
-	sys_size = (sz + 15 + 4) / 16;
-#ifdef CONFIG_EFI_STUB
-	/*
-	 * COFF requires minimum 32-byte alignment of sections, and
-	 * adding a signature is problematic without that alignment.
-	 */
-	sys_size = (sys_size + 1) & ~1;
-#endif
-
-	/* Patch the setup code with the appropriate size parameters */
-	put_unaligned_le32(sys_size, &buf[0x1f4]);
-
-	update_pecoff_text(setup_sectors * 512, i + (sys_size * 16));
+	update_pecoff_text(setup_sectors * 512, i + _edata);
 
 
 	crc = partial_crc32(buf, i, crc);
@@ -397,13 +388,6 @@ int main(int argc, char ** argv)
 	if (fwrite(kernel, 1, sz, dest) != sz)
 		die("Writing kernel failed");
 
-	/* Add padding leaving 4 bytes for the checksum */
-	while (sz++ < (sys_size*16) - 4) {
-		crc = partial_crc32_one('\0', crc);
-		if (fwrite("\0", 1, 1, dest) != 1)
-			die("Writing padding failed");
-	}
-
 	/* Write the CRC */
 	put_unaligned_le32(crc, buf);
 	if (fwrite(buf, 1, 4, dest) != 4)