vxBoot/src/loader/elf/rela.c

#include "vxBoot/loader.h"
#include "vxBoot/fs/smemfs.h"
#include "vxBoot/terminal.h"

#include <string.h>
#include <stdlib.h>

struct {
	char const * restrict const name;
	uint16_t id;
} const table[] = {
	{"R_SH_NONE", 0},
	{"R_SH_DIR32", 1},
	{"R_SH_REL32", 2},
	{"R_SH_DIR8WPN", 3},
	{"R_SH_IND12W", 4},
	{"R_SH_DIR8WPL", 5},
	{"R_SH_DIR8WPZ", 6},
	{"R_SH_DIR8BP", 7},
	{"R_SH_DIR8W", 8},
	{"R_SH_DIR8L", 9},
	{"R_SH_SWITCH16", 25},
	{"R_SH_SWITCH32", 26},
	{"R_SH_USES", 27},
	{"R_SH_COUNT", 28},
	{"R_SH_ALIGN", 29},
	{"R_SH_CODE", 30},
	{"R_SH_DATA", 31},
	{"R_SH_LABEL", 32},
	{"R_SH_SWITCH8", 33},
	{"R_SH_GNU_VTINHERIT", 4},
	{"R_SH_GNU_VTENTRY", 5},
	{"R_SH_TLS_GD_32", 144},
	{"R_SH_TLS_LD_32", 145},
	{"R_SH_TLS_LDO_32", 146},
	{"R_SH_TLS_IE_32", 147},
	{"R_SH_TLS_LE_32", 148},
	{"R_SH_TLS_DTPMOD32", 49},
	{"R_SH_TLS_DTPOFF32", 50},
	{"R_SH_TLS_TPOFF32", 51},
	{"R_SH_GOT32", 160},
	{"R_SH_PLT32", 161},
	{"R_SH_COPY", 162},
	{"R_SH_GLOB_DAT", 163},
	{"R_SH_JMP_SLOT", 164},
	{"R_SH_RELATIVE", 165},
	{"R_SH_GOTOFF", 166},
	{"R_SH_GOTPC", 167},
	{"R_SH_NUM", 256},
	{NULL, 0}
};

/* loader_reloc_symbols() : relocalize symbols */
static int loader_reloc_section(
	Elf32_Rela *rela,
	int nb_rela,
	char const * const name,
	struct kernel * const kernel
) {
	uintptr_t voff;
	uintptr_t val;
	uintptr_t loc;
	int type;

	/* logs */
	terminal_log(
		LOG_INFO,
		"   section '%s' with %d entries\n",
		name, nb_rela
	);

	/* precalculate relocalisation operation */
	voff  = (uintptr_t)kernel->hardware.ram.physical.kernel_addr;
	voff |= (uintptr_t)0x80000000;

	/* try to relocalise symbols */
	for (int i = 0; i < nb_rela; ++i) {
		type = -1;
		for (int j = 0; table[j].name != NULL; ++j) {
			if (table[j].id != ELF32_R_TYPE(rela[i].r_info))
				continue;
			if (ELF32_R_TYPE(rela[i].r_info) == R_SH_NUM)
				return (0);
			type = j;
			break;
		}
		if (type < 0) {
			terminal_write("unable to relocalize symbols %d\n", i);
			return (-1);
		}

		loc = rela[i].r_offset;
		loc += (uintptr_t)kernel->hardware.ram.physical.kernel_addr;
		loc |= (uintptr_t)0xa0000000;

		/* IMPORTANT NOTE:

		   We cannot use the real symbols value for patching the binary
		   because some symbols are completely broken and refer to
		   something else. Specially when a global use another global
		   (for example: const char * const text = "vive les g@m3rz").

		   But, after some RE, each time a global symbol is used, its
		   virtual address is set. So, for now, we just need to add the
		   relocation offset to the content of the location. */
		//val = kernel->elf.sym.tab[ELF32_R_SYM(rela[i].r_info)].st_value;
		val = *(uintptr_t*)loc;

		switch (table[type].id) {
		case R_SH_GOT32:
		case R_SH_PLT32:
		case R_SH_GOTPC:
		case R_SH_GOTOFF:
			break;
		case R_SH_DIR32:
			//terminal_log(
			//	LOG_DEBUG,
			//	"    %08x %-8s %08x\n",
			//	rela[i].r_offset,
			//	table[type].name,
			//	val
			//);
			*(uintptr_t *)loc = voff + val;
			break;
		default:
			terminal_log(
				LOG_ALERT,
				"    [%d] type %s not supported yet o(x_x)o\n",
				i, table[type].name
			);
			return (-1);
		}
	}
	return (0);
}


/* loader_rela_patch() : Try to patch the GOT/PLT section */
int loader_rela_patch(struct kernel * const kernel)
{
	Elf32_Rela *rela;
	int error;

	rela = NULL;
	for (int i = 0; i < kernel->elf.hdr.e_shnum; ++i) {
		if (kernel->elf.shdr[i].sh_type != SHT_RELA)
			continue;
		rela = realloc(rela, kernel->elf.shdr[i].sh_size);
		smemfs_pread(
			kernel->inode,
			rela,
			kernel->elf.shdr[i].sh_size,
			kernel->elf.shdr[i].sh_offset
		);
		error = loader_reloc_section(
			rela,
			kernel->elf.shdr[i].sh_size / sizeof(Elf32_Rela),
			&kernel->elf.shstrtab[kernel->elf.shdr[i].sh_name],
			kernel
		);
		if (error != 0)
			return (error);
	}
	return (0);
}