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kernel/kexec_file.c: use read-only sections in arch_kexec_apply_reloc…
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…ations*

When the relocations are applied to the purgatory only the section the
relocations are applied to is writable.  The other sections, i.e.  the
symtab and .rel/.rela, are in read-only kexec_purgatory.  Highlight this
by marking the corresponding variables as 'const'.

While at it also change the signatures of arch_kexec_apply_relocations* to
take section pointers instead of just the index of the relocation section.
This removes the second lookup and sanity check of the sections in arch
code.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Philipp Rudo <[email protected]>
Acked-by: Dave Young <[email protected]>
Cc: AKASHI Takahiro <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Thiago Jung Bauermann <[email protected]>
Cc: Vivek Goyal <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Philipp Rudo authored and torvalds committed Apr 14, 2018
1 parent 961d921 commit 8aec395
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Showing 3 changed files with 71 additions and 61 deletions.
56 changes: 20 additions & 36 deletions arch/x86/kernel/machine_kexec_64.c
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Original file line number Diff line number Diff line change
Expand Up @@ -382,52 +382,36 @@ void *arch_kexec_kernel_image_load(struct kimage *image)
/*
* Apply purgatory relocations.
*
* ehdr: Pointer to elf headers
* sechdrs: Pointer to section headers.
* relsec: section index of SHT_RELA section.
* @pi: Purgatory to be relocated.
* @section: Section relocations applying to.
* @relsec: Section containing RELAs.
* @symtabsec: Corresponding symtab.
*
* TODO: Some of the code belongs to generic code. Move that in kexec.c.
*/
int arch_kexec_apply_relocations_add(const Elf64_Ehdr *ehdr,
Elf64_Shdr *sechdrs, unsigned int relsec)
int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
Elf_Shdr *section, const Elf_Shdr *relsec,
const Elf_Shdr *symtabsec)
{
unsigned int i;
Elf64_Rela *rel;
Elf64_Sym *sym;
void *location;
Elf64_Shdr *section, *symtabsec;
unsigned long address, sec_base, value;
const char *strtab, *name, *shstrtab;
const Elf_Shdr *sechdrs;

/*
* ->sh_offset has been modified to keep the pointer to section
* contents in memory
*/
rel = (void *)sechdrs[relsec].sh_offset;

/* Section to which relocations apply */
section = &sechdrs[sechdrs[relsec].sh_info];

pr_debug("Applying relocate section %u to %u\n", relsec,
sechdrs[relsec].sh_info);

/* Associated symbol table */
symtabsec = &sechdrs[sechdrs[relsec].sh_link];

/* String table */
if (symtabsec->sh_link >= ehdr->e_shnum) {
/* Invalid strtab section number */
pr_err("Invalid string table section index %d\n",
symtabsec->sh_link);
return -ENOEXEC;
}
/* String & section header string table */
sechdrs = (void *)pi->ehdr + pi->ehdr->e_shoff;
strtab = (char *)pi->ehdr + sechdrs[symtabsec->sh_link].sh_offset;
shstrtab = (char *)pi->ehdr + sechdrs[pi->ehdr->e_shstrndx].sh_offset;

strtab = (char *)sechdrs[symtabsec->sh_link].sh_offset;
rel = (void *)pi->ehdr + relsec->sh_offset;

/* section header string table */
shstrtab = (char *)sechdrs[ehdr->e_shstrndx].sh_offset;
pr_debug("Applying relocate section %s to %u\n",
shstrtab + relsec->sh_name, relsec->sh_info);

for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
for (i = 0; i < relsec->sh_size / sizeof(*rel); i++) {

/*
* rel[i].r_offset contains byte offset from beginning
Expand All @@ -450,8 +434,8 @@ int arch_kexec_apply_relocations_add(const Elf64_Ehdr *ehdr,
* to apply. ELF64_R_SYM() and ELF64_R_TYPE() macros get
* these respectively.
*/
sym = (Elf64_Sym *)symtabsec->sh_offset +
ELF64_R_SYM(rel[i].r_info);
sym = (void *)pi->ehdr + symtabsec->sh_offset;
sym += ELF64_R_SYM(rel[i].r_info);

if (sym->st_name)
name = strtab + sym->st_name;
Expand All @@ -474,12 +458,12 @@ int arch_kexec_apply_relocations_add(const Elf64_Ehdr *ehdr,

if (sym->st_shndx == SHN_ABS)
sec_base = 0;
else if (sym->st_shndx >= ehdr->e_shnum) {
else if (sym->st_shndx >= pi->ehdr->e_shnum) {
pr_err("Invalid section %d for symbol %s\n",
sym->st_shndx, name);
return -ENOEXEC;
} else
sec_base = sechdrs[sym->st_shndx].sh_addr;
sec_base = pi->sechdrs[sym->st_shndx].sh_addr;

value = sym->st_value;
value += sec_base;
Expand Down
13 changes: 9 additions & 4 deletions include/linux/kexec.h
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Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,15 @@ struct kexec_buf {
bool top_down;
};

int __weak arch_kexec_apply_relocations_add(struct purgatory_info *pi,
Elf_Shdr *section,
const Elf_Shdr *relsec,
const Elf_Shdr *symtab);
int __weak arch_kexec_apply_relocations(struct purgatory_info *pi,
Elf_Shdr *section,
const Elf_Shdr *relsec,
const Elf_Shdr *symtab);

int __weak arch_kexec_walk_mem(struct kexec_buf *kbuf,
int (*func)(struct resource *, void *));
extern int kexec_add_buffer(struct kexec_buf *kbuf);
Expand Down Expand Up @@ -304,10 +313,6 @@ int crash_shrink_memory(unsigned long new_size);
size_t crash_get_memory_size(void);
void crash_free_reserved_phys_range(unsigned long begin, unsigned long end);

int __weak arch_kexec_apply_relocations_add(const Elf_Ehdr *ehdr,
Elf_Shdr *sechdrs, unsigned int relsec);
int __weak arch_kexec_apply_relocations(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
unsigned int relsec);
void arch_kexec_protect_crashkres(void);
void arch_kexec_unprotect_crashkres(void);

Expand Down
63 changes: 42 additions & 21 deletions kernel/kexec_file.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -110,19 +110,35 @@ int __weak arch_kexec_kernel_verify_sig(struct kimage *image, void *buf,
}
#endif

/* Apply relocations of type RELA */
/*
* arch_kexec_apply_relocations_add - apply relocations of type RELA
* @pi: Purgatory to be relocated.
* @section: Section relocations applying to.
* @relsec: Section containing RELAs.
* @symtab: Corresponding symtab.
*
* Return: 0 on success, negative errno on error.
*/
int __weak
arch_kexec_apply_relocations_add(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
unsigned int relsec)
arch_kexec_apply_relocations_add(struct purgatory_info *pi, Elf_Shdr *section,
const Elf_Shdr *relsec, const Elf_Shdr *symtab)
{
pr_err("RELA relocation unsupported.\n");
return -ENOEXEC;
}

/* Apply relocations of type REL */
/*
* arch_kexec_apply_relocations - apply relocations of type REL
* @pi: Purgatory to be relocated.
* @section: Section relocations applying to.
* @relsec: Section containing RELs.
* @symtab: Corresponding symtab.
*
* Return: 0 on success, negative errno on error.
*/
int __weak
arch_kexec_apply_relocations(const Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
unsigned int relsec)
arch_kexec_apply_relocations(struct purgatory_info *pi, Elf_Shdr *section,
const Elf_Shdr *relsec, const Elf_Shdr *symtab)
{
pr_err("REL relocation unsupported.\n");
return -ENOEXEC;
Expand Down Expand Up @@ -879,14 +895,19 @@ static int kexec_apply_relocations(struct kimage *image)
{
int i, ret;
struct purgatory_info *pi = &image->purgatory_info;
Elf_Shdr *sechdrs = pi->sechdrs;
const Elf_Shdr *sechdrs;

sechdrs = (void *)pi->ehdr + pi->ehdr->e_shoff;

/* Apply relocations */
for (i = 0; i < pi->ehdr->e_shnum; i++) {
Elf_Shdr *section, *symtab;
const Elf_Shdr *relsec;
const Elf_Shdr *symtab;
Elf_Shdr *section;

relsec = sechdrs + i;

if (sechdrs[i].sh_type != SHT_RELA &&
sechdrs[i].sh_type != SHT_REL)
if (relsec->sh_type != SHT_RELA &&
relsec->sh_type != SHT_REL)
continue;

/*
Expand All @@ -895,12 +916,12 @@ static int kexec_apply_relocations(struct kimage *image)
* symbol table. And ->sh_info contains section header
* index of section to which relocations apply.
*/
if (sechdrs[i].sh_info >= pi->ehdr->e_shnum ||
sechdrs[i].sh_link >= pi->ehdr->e_shnum)
if (relsec->sh_info >= pi->ehdr->e_shnum ||
relsec->sh_link >= pi->ehdr->e_shnum)
return -ENOEXEC;

section = &sechdrs[sechdrs[i].sh_info];
symtab = &sechdrs[sechdrs[i].sh_link];
section = pi->sechdrs + relsec->sh_info;
symtab = sechdrs + relsec->sh_link;

if (!(section->sh_flags & SHF_ALLOC))
continue;
Expand All @@ -917,12 +938,12 @@ static int kexec_apply_relocations(struct kimage *image)
* Respective architecture needs to provide support for applying
* relocations of type SHT_RELA/SHT_REL.
*/
if (sechdrs[i].sh_type == SHT_RELA)
ret = arch_kexec_apply_relocations_add(pi->ehdr,
sechdrs, i);
else if (sechdrs[i].sh_type == SHT_REL)
ret = arch_kexec_apply_relocations(pi->ehdr,
sechdrs, i);
if (relsec->sh_type == SHT_RELA)
ret = arch_kexec_apply_relocations_add(pi, section,
relsec, symtab);
else if (relsec->sh_type == SHT_REL)
ret = arch_kexec_apply_relocations(pi, section,
relsec, symtab);
if (ret)
return ret;
}
Expand Down

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