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linux/arch/alpha/kernel/module.c
Edward Humes b6b17a8b3e alpha: fix R_ALPHA_LITERAL reloc for large modules 
Previously, R_ALPHA_LITERAL relocations would overflow for large kernel
modules.

This was because the Alpha's apply_relocate_add was relying on the kernel's
module loader to have sorted the GOT towards the very end of the module as it
was mapped into memory in order to correctly assign the global pointer. While
this behavior would mostly work fine for small kernel modules, this approach
would overflow on kernel modules with large GOT's since the global pointer
would be very far away from the GOT, and thus, certain entries would be out of
range.

This patch fixes this by instead using the Tru64 behavior of assigning the
global pointer to be 32KB away from the start of the GOT. The change made
in this patch won't work for multi-GOT kernel modules as it makes the
assumption the module only has one GOT located at the beginning of .got,
although for the vast majority kernel modules, this should be fine. Of the
kernel modules that would previously result in a relocation error, none of
them, even modules like nouveau, have even come close to filling up a single
GOT, and they've all worked fine under this patch.

Signed-off-by: Edward Humes <aurxenon@lunos.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>
2023-02-14 12:37:18 -05:00

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// SPDX-License-Identifier: GPL-2.0-or-later
/* Kernel module help for Alpha.
Copyright (C) 2002 Richard Henderson.
*/
#include <linux/moduleloader.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#if 0
#define DEBUGP printk
#else
#define DEBUGP(fmt...)
#endif
/* Allocate the GOT at the end of the core sections. */
struct got_entry {
struct got_entry *next;
Elf64_Sxword r_addend;
int got_offset;
};
static inline void
process_reloc_for_got(Elf64_Rela *rela,
struct got_entry *chains, Elf64_Xword *poffset)
{
unsigned long r_sym = ELF64_R_SYM (rela->r_info);
unsigned long r_type = ELF64_R_TYPE (rela->r_info);
Elf64_Sxword r_addend = rela->r_addend;
struct got_entry *g;
if (r_type != R_ALPHA_LITERAL)
return;
for (g = chains + r_sym; g ; g = g->next)
if (g->r_addend == r_addend) {
if (g->got_offset == 0) {
g->got_offset = *poffset;
*poffset += 8;
}
goto found_entry;
}
g = kmalloc (sizeof (*g), GFP_KERNEL);
g->next = chains[r_sym].next;
g->r_addend = r_addend;
g->got_offset = *poffset;
*poffset += 8;
chains[r_sym].next = g;
found_entry:
/* Trick: most of the ELF64_R_TYPE field is unused. There are
42 valid relocation types, and a 32-bit field. Co-opt the
bits above 256 to store the got offset for this reloc. */
rela->r_info |= g->got_offset << 8;
}
int
module_frob_arch_sections(Elf64_Ehdr *hdr, Elf64_Shdr *sechdrs,
char *secstrings, struct module *me)
{
struct got_entry *chains;
Elf64_Rela *rela;
Elf64_Shdr *esechdrs, *symtab, *s, *got;
unsigned long nsyms, nrela, i;
esechdrs = sechdrs + hdr->e_shnum;
symtab = got = NULL;
/* Find out how large the symbol table is. Allocate one got_entry
head per symbol. Normally this will be enough, but not always.
We'll chain different offsets for the symbol down each head. */
for (s = sechdrs; s < esechdrs; ++s)
if (s->sh_type == SHT_SYMTAB)
symtab = s;
else if (!strcmp(".got", secstrings + s->sh_name)) {
got = s;
me->arch.gotsecindex = s - sechdrs;
}
if (!symtab) {
printk(KERN_ERR "module %s: no symbol table\n", me->name);
return -ENOEXEC;
}
if (!got) {
printk(KERN_ERR "module %s: no got section\n", me->name);
return -ENOEXEC;
}
nsyms = symtab->sh_size / sizeof(Elf64_Sym);
chains = kcalloc(nsyms, sizeof(struct got_entry), GFP_KERNEL);
if (!chains) {
printk(KERN_ERR
"module %s: no memory for symbol chain buffer\n",
me->name);
return -ENOMEM;
}
got->sh_size = 0;
got->sh_addralign = 8;
got->sh_type = SHT_NOBITS;
/* Examine all LITERAL relocations to find out what GOT entries
are required. This sizes the GOT section as well. */
for (s = sechdrs; s < esechdrs; ++s)
if (s->sh_type == SHT_RELA) {
nrela = s->sh_size / sizeof(Elf64_Rela);
rela = (void *)hdr + s->sh_offset;
for (i = 0; i < nrela; ++i)
process_reloc_for_got(rela+i, chains,
&got->sh_size);
}
/* Free the memory we allocated. */
for (i = 0; i < nsyms; ++i) {
struct got_entry *g, *n;
for (g = chains[i].next; g ; g = n) {
n = g->next;
kfree(g);
}
}
kfree(chains);
return 0;
}
int
apply_relocate_add(Elf64_Shdr *sechdrs, const char *strtab,
unsigned int symindex, unsigned int relsec,
struct module *me)
{
Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
unsigned long i, n = sechdrs[relsec].sh_size / sizeof(*rela);
Elf64_Sym *symtab, *sym;
void *base, *location;
unsigned long got, gp;
DEBUGP("Applying relocate section %u to %u\n", relsec,
sechdrs[relsec].sh_info);
base = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr;
symtab = (Elf64_Sym *)sechdrs[symindex].sh_addr;
got = sechdrs[me->arch.gotsecindex].sh_addr;
gp = got + 0x8000;
for (i = 0; i < n; i++) {
unsigned long r_sym = ELF64_R_SYM (rela[i].r_info);
unsigned long r_type = ELF64_R_TYPE (rela[i].r_info);
unsigned long r_got_offset = r_type >> 8;
unsigned long value, hi, lo;
r_type &= 0xff;
/* This is where to make the change. */
location = base + rela[i].r_offset;
/* This is the symbol it is referring to. Note that all
unresolved symbols have been resolved. */
sym = symtab + r_sym;
value = sym->st_value + rela[i].r_addend;
switch (r_type) {
case R_ALPHA_NONE:
break;
case R_ALPHA_REFLONG:
*(u32 *)location = value;
break;
case R_ALPHA_REFQUAD:
/* BUG() can produce misaligned relocations. */
((u32 *)location)[0] = value;
((u32 *)location)[1] = value >> 32;
break;
case R_ALPHA_GPREL32:
value -= gp;
if ((int)value != value)
goto reloc_overflow;
*(u32 *)location = value;
break;
case R_ALPHA_LITERAL:
hi = got + r_got_offset;
lo = hi - gp;
if ((short)lo != lo)
goto reloc_overflow;
*(u16 *)location = lo;
*(u64 *)hi = value;
break;
case R_ALPHA_LITUSE:
break;
case R_ALPHA_GPDISP:
value = gp - (u64)location;
lo = (short)value;
hi = (int)(value - lo);
if (hi + lo != value)
goto reloc_overflow;
*(u16 *)location = hi >> 16;
*(u16 *)(location + rela[i].r_addend) = lo;
break;
case R_ALPHA_BRSGP:
/* BRSGP is only allowed to bind to local symbols.
If the section is undef, this means that the
value was resolved from somewhere else. */
if (sym->st_shndx == SHN_UNDEF)
goto reloc_overflow;
if ((sym->st_other & STO_ALPHA_STD_GPLOAD) ==
STO_ALPHA_STD_GPLOAD)
/* Omit the prologue. */
value += 8;
fallthrough;
case R_ALPHA_BRADDR:
value -= (u64)location + 4;
if (value & 3)
goto reloc_overflow;
value = (long)value >> 2;
if (value + (1<<21) >= 1<<22)
goto reloc_overflow;
value &= 0x1fffff;
value |= *(u32 *)location & ~0x1fffff;
*(u32 *)location = value;
break;
case R_ALPHA_HINT:
break;
case R_ALPHA_SREL32:
value -= (u64)location;
if ((int)value != value)
goto reloc_overflow;
*(u32 *)location = value;
break;
case R_ALPHA_SREL64:
value -= (u64)location;
*(u64 *)location = value;
break;
case R_ALPHA_GPRELHIGH:
value = (long)(value - gp + 0x8000) >> 16;
if ((short) value != value)
goto reloc_overflow;
*(u16 *)location = value;
break;
case R_ALPHA_GPRELLOW:
value -= gp;
*(u16 *)location = value;
break;
case R_ALPHA_GPREL16:
value -= gp;
if ((short) value != value)
goto reloc_overflow;
*(u16 *)location = value;
break;
default:
printk(KERN_ERR "module %s: Unknown relocation: %lu\n",
me->name, r_type);
return -ENOEXEC;
reloc_overflow:
if (ELF64_ST_TYPE (sym->st_info) == STT_SECTION)
printk(KERN_ERR
"module %s: Relocation (type %lu) overflow vs section %d\n",
me->name, r_type, sym->st_shndx);
else
printk(KERN_ERR
"module %s: Relocation (type %lu) overflow vs %s\n",
me->name, r_type, strtab + sym->st_name);
return -ENOEXEC;
}
}
return 0;
}
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