Commit a8327be7 authored by Brian Gerst's avatar Brian Gerst Committed by Ingo Molnar
Browse files

x86/boot/64: Remove inverse relocations 



Inverse relocations were needed to offset the effects of relocation for
RIP-relative accesses to zero-based percpu data.  Now that the percpu
section is linked normally as part of the kernel image, they are no
longer needed.

Signed-off-by: default avatarBrian Gerst <brgerst@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250123190747.745588-11-brgerst@gmail.com
parent b5c4f953

arch/x86/boot/compressed/misc.c

+1 −13
Original line number Diff line number Diff line
@@ -235,7 +235,7 @@ static void handle_relocations(void *output, unsigned long output_len, 


	/*

	 * Process relocations: 32 bit relocations first then 64 bit after.

	 * Three sets of binary relocations are added to the end of the kernel

	 * Two sets of binary relocations are added to the end of the kernel

	 * before compression. Each relocation table entry is the kernel

	 * address of the location which needs to be updated stored as a

	 * 32-bit value which is sign extended to 64 bits.
@@ -245,8 +245,6 @@ static void handle_relocations(void *output, unsigned long output_len, 
	 * kernel bits...

	 * 0 - zero terminator for 64 bit relocations

	 * 64 bit relocation repeated

	 * 0 - zero terminator for inverse 32 bit relocations

	 * 32 bit inverse relocation repeated

	 * 0 - zero terminator for 32 bit relocations

	 * 32 bit relocation repeated

	 *
@@ -263,16 +261,6 @@ static void handle_relocations(void *output, unsigned long output_len, 
		*(uint32_t *)ptr += delta;

	}

#ifdef CONFIG_X86_64

	while (*--reloc) {

		long extended = *reloc;

		extended += map;



		ptr = (unsigned long)extended;

		if (ptr < min_addr || ptr > max_addr)

			error("inverse 32-bit relocation outside of kernel!\n");



		*(int32_t *)ptr -= delta;

	}

	for (reloc--; *reloc; reloc--) {

		long extended = *reloc;

		extended += map;

arch/x86/tools/relocs.c

+1 −129
Original line number Diff line number Diff line
@@ -29,7 +29,6 @@ static struct relocs relocs16; 
static struct relocs		relocs32;



#if ELF_BITS == 64

static struct relocs		relocs32neg;

static struct relocs		relocs64;

# define FMT PRIu64
@@ -91,7 +90,6 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = { 
	"__initramfs_start|"

	"(jiffies|jiffies_64)|"

#if ELF_BITS == 64

	"__per_cpu_load|"

	"init_per_cpu__.*|"

	"__end_rodata_hpage_align|"

#endif
@@ -290,34 +288,6 @@ static const char *sym_name(const char *sym_strtab, Elf_Sym *sym) 
	return name;

}



static Elf_Sym *sym_lookup(const char *symname)

{

	int i;



	for (i = 0; i < shnum; i++) {

		struct section *sec = &secs[i];

		long nsyms;

		char *strtab;

		Elf_Sym *symtab;

		Elf_Sym *sym;



		if (sec->shdr.sh_type != SHT_SYMTAB)

			continue;



		nsyms = sec->shdr.sh_size/sizeof(Elf_Sym);

		symtab = sec->symtab;

		strtab = sec->link->strtab;



		for (sym = symtab; --nsyms >= 0; sym++) {

			if (!sym->st_name)

				continue;

			if (strcmp(symname, strtab + sym->st_name) == 0)

				return sym;

		}

	}

	return 0;

}



#if BYTE_ORDER == LITTLE_ENDIAN

# define le16_to_cpu(val)	(val)

# define le32_to_cpu(val)	(val)
@@ -766,78 +736,8 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel, 
	}

}



/*

 * The .data..percpu section is a special case for x86_64 SMP kernels.

 * It is used to initialize the actual per_cpu areas and to provide

 * definitions for the per_cpu variables that correspond to their offsets

 * within the percpu area. Since the values of all of the symbols need

 * to be offsets from the start of the per_cpu area the virtual address

 * (sh_addr) of .data..percpu is 0 in SMP kernels.

 *

 * This means that:

 *

 *	Relocations that reference symbols in the per_cpu area do not

 *	need further relocation (since the value is an offset relative

 *	to the start of the per_cpu area that does not change).

 *

 *	Relocations that apply to the per_cpu area need to have their

 *	offset adjusted by by the value of __per_cpu_load to make them

 *	point to the correct place in the loaded image (because the

 *	virtual address of .data..percpu is 0).

 *

 * For non SMP kernels .data..percpu is linked as part of the normal

 * kernel data and does not require special treatment.

 *

 */

static int per_cpu_shndx = -1;

static Elf_Addr per_cpu_load_addr;



static void percpu_init(void)

{

	int i;



	for (i = 0; i < shnum; i++) {

		ElfW(Sym) *sym;



		if (strcmp(sec_name(i), ".data..percpu"))

			continue;



		if (secs[i].shdr.sh_addr != 0)	/* non SMP kernel */

			return;



		sym = sym_lookup("__per_cpu_load");

		if (!sym)

			die("can't find __per_cpu_load\n");



		per_cpu_shndx = i;

		per_cpu_load_addr = sym->st_value;



		return;

	}

}



#if ELF_BITS == 64



/*

 * Check to see if a symbol lies in the .data..percpu section.

 *

 * The linker incorrectly associates some symbols with the

 * .data..percpu section so we also need to check the symbol

 * name to make sure that we classify the symbol correctly.

 *

 * The GNU linker incorrectly associates:

 *	__init_begin

 *	__per_cpu_load

 *

 * The "gold" linker incorrectly associates:

 *	init_per_cpu__gdt_page

 */

static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)

{

	return 0;

}





static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,

		      const char *symname)

{
@@ -848,12 +748,6 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, 
	if (sym->st_shndx == SHN_UNDEF)

		return 0;



	/*

	 * Adjust the offset if this reloc applies to the percpu section.

	 */

	if (sec->shdr.sh_info == per_cpu_shndx)

		offset += per_cpu_load_addr;



	switch (r_type) {

	case R_X86_64_NONE:

		/* NONE can be ignored. */
@@ -863,32 +757,21 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, 
	case R_X86_64_PLT32:

	case R_X86_64_REX_GOTPCRELX:

		/*

		 * PC relative relocations don't need to be adjusted unless

		 * referencing a percpu symbol.

		 * PC relative relocations don't need to be adjusted.

		 *

		 * NB: R_X86_64_PLT32 can be treated as R_X86_64_PC32.

		 */

		if (is_percpu_sym(sym, symname))

			add_reloc(&relocs32neg, offset);

		break;



	case R_X86_64_PC64:

		/*

		 * Only used by jump labels

		 */

		if (is_percpu_sym(sym, symname))

			die("Invalid R_X86_64_PC64 relocation against per-CPU symbol %s\n", symname);

		break;



	case R_X86_64_32:

	case R_X86_64_32S:

	case R_X86_64_64:

		/*

		 * References to the percpu area don't need to be adjusted.

		 */

		if (is_percpu_sym(sym, symname))

			break;



		if (shn_abs) {

			/*

			 * Whitelisted absolute symbols do not require
@@ -1101,7 +984,6 @@ static void emit_relocs(int as_text, int use_real_mode) 
	/* Order the relocations for more efficient processing */

	sort_relocs(&relocs32);

#if ELF_BITS == 64

	sort_relocs(&relocs32neg);

	sort_relocs(&relocs64);

#else

	sort_relocs(&relocs16);
@@ -1133,13 +1015,6 @@ static void emit_relocs(int as_text, int use_real_mode) 
		/* Now print each relocation */

		for (i = 0; i < relocs64.count; i++)

			write_reloc(relocs64.offset[i], stdout);



		/* Print a stop */

		write_reloc(0, stdout);



		/* Now print each inverse 32-bit relocation */

		for (i = 0; i < relocs32neg.count; i++)

			write_reloc(relocs32neg.offset[i], stdout);

#endif



		/* Print a stop */
@@ -1192,9 +1067,6 @@ void process(FILE *fp, int use_real_mode, int as_text, 
	read_symtabs(fp);

	read_relocs(fp);



	if (ELF_BITS == 64)

		percpu_init();



	if (show_absolute_syms) {

		print_absolute_symbols();

		return;