Commit 8aec395b authored by Philipp Rudo's avatar Philipp Rudo Committed by Linus Torvalds
Browse files

kernel/kexec_file.c: use read-only sections in arch_kexec_apply_relocations* 

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/20180321112751.22196-6-prudo@linux.vnet.ibm.com


Signed-off-by: default avatarPhilipp Rudo <prudo@linux.vnet.ibm.com>
Acked-by: default avatarDave Young <dyoung@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 961d921a

arch/x86/kernel/machine_kexec_64.c

+20 −36
Original line number Diff line number Diff line
@@ -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
@@ -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;
@@ -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;

include/linux/kexec.h

+9 −4
Original line number Diff line number Diff line
@@ -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);
@@ -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);

kernel/kexec_file.c

+42 −21
Original line number Diff line number Diff line
@@ -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;
@@ -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;



		/*
@@ -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;
@@ -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;

	}

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