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0c05e7bd2d
Josh reported a bug:
When the object to be patched is a module, and that module is
rmmod'ed and reloaded, it fails to load with:
module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c
livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
The livepatch module has a relocation which references a symbol
in the _previous_ loading of nfsd. When apply_relocate_add()
tries to replace the old relocation with a new one, it sees that
the previous one is nonzero and it errors out.
He also proposed three different solutions. We could remove the error
check in apply_relocate_add() introduced by commit eda9cec4c9
("x86/module: Detect and skip invalid relocations"). However the check
is useful for detecting corrupted modules.
We could also deny the patched modules to be removed. If it proved to be
a major drawback for users, we could still implement a different
approach. The solution would also complicate the existing code a lot.
We thus decided to reverse the relocation patching (clear all relocation
targets on x86_64). The solution is not
universal and is too much arch-specific, but it may prove to be simpler
in the end.
Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
Originally-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Joe Lawrence <joe.lawrence@redhat.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230125185401.279042-2-song@kernel.org
124 lines
3.8 KiB
C
124 lines
3.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_MODULELOADER_H
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#define _LINUX_MODULELOADER_H
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/* The stuff needed for archs to support modules. */
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#include <linux/module.h>
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#include <linux/elf.h>
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/* These may be implemented by architectures that need to hook into the
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* module loader code. Architectures that don't need to do anything special
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* can just rely on the 'weak' default hooks defined in kernel/module.c.
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* Note, however, that at least one of apply_relocate or apply_relocate_add
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* must be implemented by each architecture.
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*/
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/* Adjust arch-specific sections. Return 0 on success. */
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int module_frob_arch_sections(Elf_Ehdr *hdr,
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Elf_Shdr *sechdrs,
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char *secstrings,
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struct module *mod);
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/* Additional bytes needed by arch in front of individual sections */
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unsigned int arch_mod_section_prepend(struct module *mod, unsigned int section);
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/* Allocator used for allocating struct module, core sections and init
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sections. Returns NULL on failure. */
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void *module_alloc(unsigned long size);
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/* Free memory returned from module_alloc. */
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void module_memfree(void *module_region);
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/* Determines if the section name is an init section (that is only used during
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* module loading).
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*/
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bool module_init_section(const char *name);
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/* Determines if the section name is an exit section (that is only used during
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* module unloading)
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*/
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bool module_exit_section(const char *name);
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/*
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* Apply the given relocation to the (simplified) ELF. Return -error
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* or 0.
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*/
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#ifdef CONFIG_MODULES_USE_ELF_REL
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int apply_relocate(Elf_Shdr *sechdrs,
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const char *strtab,
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unsigned int symindex,
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unsigned int relsec,
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struct module *mod);
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#else
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static inline int apply_relocate(Elf_Shdr *sechdrs,
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const char *strtab,
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unsigned int symindex,
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unsigned int relsec,
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struct module *me)
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{
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printk(KERN_ERR "module %s: REL relocation unsupported\n",
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module_name(me));
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return -ENOEXEC;
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}
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#endif
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/*
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* Apply the given add relocation to the (simplified) ELF. Return
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* -error or 0
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*/
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#ifdef CONFIG_MODULES_USE_ELF_RELA
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int apply_relocate_add(Elf_Shdr *sechdrs,
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const char *strtab,
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unsigned int symindex,
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unsigned int relsec,
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struct module *mod);
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#ifdef CONFIG_LIVEPATCH
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/*
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* Some architectures (namely x86_64 and ppc64) perform sanity checks when
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* applying relocations. If a patched module gets unloaded and then later
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* reloaded (and re-patched), klp re-applies relocations to the replacement
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* function(s). Any leftover relocations from the previous loading of the
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* patched module might trigger the sanity checks.
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*
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* To prevent that, when unloading a patched module, clear out any relocations
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* that might trigger arch-specific sanity checks on a future module reload.
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*/
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void clear_relocate_add(Elf_Shdr *sechdrs,
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const char *strtab,
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unsigned int symindex,
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unsigned int relsec,
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struct module *me);
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#endif
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#else
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static inline int apply_relocate_add(Elf_Shdr *sechdrs,
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const char *strtab,
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unsigned int symindex,
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unsigned int relsec,
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struct module *me)
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{
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printk(KERN_ERR "module %s: REL relocation unsupported\n",
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module_name(me));
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return -ENOEXEC;
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}
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#endif
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/* Any final processing of module before access. Return -error or 0. */
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int module_finalize(const Elf_Ehdr *hdr,
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const Elf_Shdr *sechdrs,
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struct module *mod);
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/* Any cleanup needed when module leaves. */
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void module_arch_cleanup(struct module *mod);
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/* Any cleanup before freeing mod->module_init */
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void module_arch_freeing_init(struct module *mod);
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#if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
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!defined(CONFIG_KASAN_VMALLOC)
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#include <linux/kasan.h>
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#define MODULE_ALIGN (PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT)
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#else
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#define MODULE_ALIGN PAGE_SIZE
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#endif
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#endif
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