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x86/boot/64: Remove inverse relocations

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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: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250123190747.745588-11-brgerst@gmail.com
This commit is contained in:
Brian Gerst 2025-01-23 14:07:42 -05:00 committed by Ingo Molnar
parent b5c4f95351
commit a8327be7b2
2 changed files with 2 additions and 142 deletions
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14
arch/x86/boot/compressed/misc.c
View File

@ -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;

130
arch/x86/tools/relocs.c
View File

@ -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;