[PATCH 12/17] x86/boot: Derive file size from _edata symbol

Ard Biesheuvel
2023-08-18T13:46:26Z

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.

Note that the resulting binary is identical (for CONFIG_EFI_STUB=y
builds)

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/Makefile | 2 +-
arch/x86/boot/compressed/vmlinux.lds.S | 3 ++
arch/x86/boot/header.S | 2 +-
arch/x86/boot/tools/build.c | 30 +++++---------------
4 files changed, 12 insertions(+), 25 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index be1e8b94c93afa4a..b26e30a2d865f72d 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -90,7 +90,7 @@ $(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 4ff6ab1b67d9b336..5326f3b441948c5d 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 bef9265173757a5a..f1fdffc9d2ca984b 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -237,7 +237,7 @@ sentinel: .byte 0xff, 0xff /* Used to detect broken loaders */
hdr:
setup_sects: .byte (setup_size / 512) - 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 665ce7241542e475..082c38a097713a2d 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -55,6 +55,7 @@ u8 buf[(SETUP_SECT_NUM+1)*512];

static unsigned long efi_pe_entry;
static unsigned long efi32_pe_entry;
+static unsigned long _edata;
static unsigned long _end;

/*----------------------------------------------------------------------*/
@@ -311,6 +312,7 @@ 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');
@@ -323,7 +325,6 @@ 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;
@@ -372,24 +373,14 @@ 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);
@@ -401,13 +392,6 @@ 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)
--
2.39.2