[PATCH 05/17] x86/boot: Omit compression buffer from PE/COFF image memory footprint

Ard Biesheuvel
2023-08-18T13:45:53Z

Now that the EFI stub decompresses the kernel and hands over to the
decompressed image directly, there is no longer a need to provide a
decompression buffer as part of the .BSS allocation of the PE/COFF
image. It also means the PE/COFF image can be loaded anywhere in memory,
and setting the preferred image base is unnecessary. So drop the
handling of this from the header and from the build tool.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/header.S | 6 +--
arch/x86/boot/tools/build.c | 50 +++-----------------
2 files changed, 8 insertions(+), 48 deletions(-)

diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index b24fa50a98986945..a87d9133384b0986 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -90,12 +90,10 @@ optional_header:
#endif

extra_header_fields:
- # PE specification requires ImageBase to be 64k aligned
- .set image_base, (LOAD_PHYSICAL_ADDR + 0xffff) & ~0xffff
#ifdef CONFIG_X86_32
- .long image_base # ImageBase
+ .long 0 # ImageBase
#else
- .quad image_base # ImageBase
+ .quad 0 # ImageBase
#endif
.long 0x20 # SectionAlignment
.long 0x20 # FileAlignment
diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index bd247692b70174f0..0354c223e35492b6 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -65,7 +65,6 @@ static unsigned long efi_pe_entry;
static unsigned long efi32_pe_entry;
static unsigned long kernel_info;
static unsigned long startup_64;
-static unsigned long _ehead;
static unsigned long _end;

/*----------------------------------------------------------------------*/
@@ -229,27 +228,14 @@ static void update_pecoff_setup_and_reloc(unsigned int size)
#endif
}

-static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
- unsigned int init_sz)
+static void update_pecoff_text(unsigned int text_start, unsigned int file_sz)
{
unsigned int pe_header;
unsigned int text_sz = file_sz - text_start;
- unsigned int bss_sz = init_sz - file_sz;
+ unsigned int bss_sz = _end - text_sz;

pe_header = get_unaligned_le32(&buf[0x3c]);

- /*
- * The PE/COFF loader may load the image at an address which is
- * misaligned with respect to the kernel_alignment field in the setup
- * header.
- *
- * In order to avoid relocating the kernel to correct the misalignment,
- * add slack to allow the buffer to be aligned within the declared size
- * of the image.
- */
- bss_sz += CONFIG_PHYSICAL_ALIGN;
- init_sz += CONFIG_PHYSICAL_ALIGN;
-
/*
* Size of code: Subtract the size of the first sector (512 bytes)
* which includes the header.
@@ -257,7 +243,7 @@ static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
put_unaligned_le32(file_sz - 512 + bss_sz, &buf[pe_header + 0x1c]);

/* Size of image */
- put_unaligned_le32(init_sz, &buf[pe_header + 0x50]);
+ put_unaligned_le32(file_sz + bss_sz, &buf[pe_header + 0x50]);

/*
* Address of entry point for PE/COFF executable
@@ -308,8 +294,7 @@ static void efi_stub_entry_update(void)

static inline void update_pecoff_setup_and_reloc(unsigned int size) {}
static inline void update_pecoff_text(unsigned int text_start,
- unsigned int file_sz,
- unsigned int init_sz) {}
+ unsigned int file_sz) {}
static inline void efi_stub_defaults(void) {}
static inline void efi_stub_entry_update(void) {}

@@ -360,7 +345,6 @@ static void parse_zoffset(char *fname)
PARSE_ZOFS(p, efi32_pe_entry);
PARSE_ZOFS(p, kernel_info);
PARSE_ZOFS(p, startup_64);
- PARSE_ZOFS(p, _ehead);
PARSE_ZOFS(p, _end);

p = strchr(p, '\n');
@@ -371,7 +355,7 @@ static void parse_zoffset(char *fname)

int main(int argc, char ** argv)
{
- unsigned int i, sz, setup_sectors, init_sz;
+ unsigned int i, sz, setup_sectors;
int c;
u32 sys_size;
struct stat sb;
@@ -442,31 +426,9 @@ int main(int argc, char ** argv)
buf[0x1f1] = setup_sectors-1;
put_unaligned_le32(sys_size, &buf[0x1f4]);

- init_sz = get_unaligned_le32(&buf[0x260]);
-#ifdef CONFIG_EFI_STUB
- /*
- * The decompression buffer will start at ImageBase. When relocating
- * the compressed kernel to its end, we must ensure that the head
- * section does not get overwritten. The head section occupies
- * [i, i + _ehead), and the destination is [init_sz - _end, init_sz).
- *
- * At present these should never overlap, because 'i' is at most 32k
- * because of SETUP_SECT_MAX, '_ehead' is less than 1k, and the
- * calculation of INIT_SIZE in boot/header.S ensures that
- * 'init_sz - _end' is at least 64k.
- *
- * For future-proofing, increase init_sz if necessary.
- */
-
- if (init_sz - _end < i + _ehead) {
- init_sz = (i + _ehead + _end + 4095) & ~4095;
- put_unaligned_le32(init_sz, &buf[0x260]);
- }
-#endif
- update_pecoff_text(setup_sectors * 512, i + (sys_size * 16), init_sz);
+ update_pecoff_text(setup_sectors * 512, i + (sys_size * 16));

efi_stub_entry_update();
-
/* Update kernel_info offset. */
put_unaligned_le32(kernel_info, &buf[0x268]);

--
2.39.2