[syslinux] [PATCH 2/4] efi: Location, size and alignment of .text section

[Celelibi]

In the generated PE file, the section header for the .text section used
to address more than the whole file. Starting at offset 0 (before the
end of the headers) is illegal and is rejected by OVMF. Giving a size
greater than the actual file size is also illegal and rejected.

Moreover, the actual data inside the PE file have to be aligned to at
least 512 bytes. Hence, .text need to be aligned as well.

Signed-off-by: Celelibi <celelibi at gmail.com>
---
 efi/wrapper.c | 44 +++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/efi/wrapper.c b/efi/wrapper.c
index ec77271..bd2c175 100644
--- a/efi/wrapper.c
+++ b/efi/wrapper.c
@@ -54,11 +54,15 @@ static void write_header(FILE *f, __uint32_t entry, size_t data_size,
 	struct coff_hdr c_hdr;
 	struct header hdr;
 	struct coff_reloc c_rel;
-	__uint32_t total_sz = so_size;
+	__uint32_t total_sz = data_size;
 	__uint32_t dummy = 0;
 	__uint32_t hdr_sz;
 	__uint32_t reloc_start, reloc_end;
 
+	hdr_sz = 512;
+	total_sz += hdr_sz;
+	entry += hdr_sz;
+
 	memset(&hdr, 0, sizeof(hdr));
 	hdr.msdos_signature = MSDOS_SIGNATURE;
 
@@ -77,11 +81,6 @@ static void write_header(FILE *f, __uint32_t entry, size_t data_size,
 	c_hdr.nr_sections = 2;
 	c_hdr.nr_syms = 1;
 	if (class == ELFCLASS32) {
-		hdr_sz = sizeof(o_hdr) + sizeof(t_sec) + sizeof(e_hdr) +
-				sizeof(r_sec) + sizeof(c_hdr) + sizeof(hdr) + sizeof(c_rel)
-				+ sizeof(dummy);
-		total_sz += hdr_sz;
-		entry += hdr_sz;
 		c_hdr.arch = IMAGE_FILE_MACHINE_I386;
 		c_hdr.characteristics = IMAGE_FILE_32BIT_MACHINE |
 			IMAGE_FILE_DEBUG_STRIPPED | IMAGE_FILE_EXECUTABLE_IMAGE |
@@ -92,25 +91,20 @@ static void write_header(FILE *f, __uint32_t entry, size_t data_size,
 		o_hdr.format = PE32_FORMAT;
 		o_hdr.major_linker_version = 0x02;
 		o_hdr.minor_linker_version = 0x14;
-		o_hdr.code_sz = total_sz;
+		o_hdr.code_sz = data_size;
 		o_hdr.entry_point = entry;
 		o_hdr.initialized_data_sz = data_size;
 		fwrite(&o_hdr, sizeof(o_hdr), 1, f);
 		memset(&e_hdr, 0, sizeof(e_hdr));
 		e_hdr.section_align = 4096;
 		e_hdr.file_align = 512;
-		e_hdr.image_sz = total_sz;
-		e_hdr.headers_sz = 512;
+		e_hdr.image_sz = hdr_sz + so_size;
+		e_hdr.headers_sz = hdr_sz;
 		e_hdr.subsystem = IMAGE_SUBSYSTEM_EFI_APPLICATION;
 		e_hdr.rva_and_sizes_nr = sizeof(e_hdr.data_directory) / sizeof(__uint64_t);
 		fwrite(&e_hdr, sizeof(e_hdr), 1, f);
 	}
 	else if (class == ELFCLASS64) {
-		hdr_sz = sizeof(o_hdr_pe32p) + sizeof(t_sec) + sizeof(e_hdr_pe32p) +
-				sizeof(r_sec) + sizeof(c_hdr) + sizeof(hdr) + sizeof(c_rel)
-				+ sizeof(dummy);
-		total_sz += hdr_sz;
-		entry += hdr_sz;
 		c_hdr.arch = IMAGE_FILE_MACHINE_X86_64;
 		c_hdr.characteristics = IMAGE_FILE_DEBUG_STRIPPED | IMAGE_FILE_EXECUTABLE_IMAGE |
 			IMAGE_FILE_LINE_NUMBERS_STRIPPED;
@@ -120,15 +114,15 @@ static void write_header(FILE *f, __uint32_t entry, size_t data_size,
 		o_hdr_pe32p.format = PE32P_FORMAT;
 		o_hdr_pe32p.major_linker_version = 0x02;
 		o_hdr_pe32p.minor_linker_version = 0x14;
-		o_hdr_pe32p.code_sz = total_sz;
+		o_hdr_pe32p.code_sz = data_size;
 		o_hdr_pe32p.entry_point = entry;
 		o_hdr.initialized_data_sz = data_size;
 		fwrite(&o_hdr_pe32p, sizeof(o_hdr_pe32p), 1, f);
 		memset(&e_hdr_pe32p, 0, sizeof(e_hdr));
 		e_hdr_pe32p.section_align = 4096;
 		e_hdr_pe32p.file_align = 512;
-		e_hdr_pe32p.image_sz = total_sz;
-		e_hdr_pe32p.headers_sz = 512;
+		e_hdr_pe32p.image_sz = hdr_sz + so_size;
+		e_hdr_pe32p.headers_sz = hdr_sz;
 		e_hdr_pe32p.subsystem = IMAGE_SUBSYSTEM_EFI_APPLICATION;
 		e_hdr_pe32p.rva_and_sizes_nr = sizeof(e_hdr_pe32p.data_directory) / sizeof(__uint64_t);
 		fwrite(&e_hdr_pe32p, sizeof(e_hdr_pe32p), 1, f);
@@ -136,8 +130,10 @@ static void write_header(FILE *f, __uint32_t entry, size_t data_size,
 
 	memset(&t_sec, 0, sizeof(t_sec));
 	strcpy((char *)t_sec.name, ".text");
-	t_sec.virtual_sz = total_sz;
-	t_sec.raw_data_sz = total_sz;
+	t_sec.virtual_sz = data_size;
+	t_sec.virtual_address = hdr_sz;
+	t_sec.raw_data_sz = t_sec.virtual_sz;
+	t_sec.raw_data = t_sec.virtual_address;
 	t_sec.characteristics = IMAGE_SCN_CNT_CODE |
 		IMAGE_SCN_ALIGN_16BYTES | IMAGE_SCN_MEM_EXECUTE |
 		IMAGE_SCN_MEM_READ;
@@ -163,6 +159,16 @@ static void write_header(FILE *f, __uint32_t entry, size_t data_size,
 	fwrite(&c_rel, sizeof(c_rel), 1, f);
 	fwrite(&dummy, sizeof(dummy), 1, f);
 
+	/*
+	 * Add some padding to align the ELF as needed
+	 */
+	if (ftell(f) > t_sec.virtual_address) {
+		// A fseek that rewind would be a bug hard to track
+		fprintf(stderr, "PE+ headers are too large.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	fseek(f, t_sec.virtual_address, SEEK_SET);
 }
 
 static void usage(char *progname)
-- 
1.8.4.3