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.
On ppc64le, we have a similar issue:
module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
He also proposed three different solutions. We could remove the error
check in apply_relocate_add() introduced by commit eda9cec4c9a1
("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, or return back nops on powerpc). 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 <[email protected]>
Signed-off-by: Miroslav Benes <[email protected]>
---
arch/powerpc/kernel/module_64.c | 45 +++++++++++++++++++++++++++++++++
arch/s390/kernel/module.c | 8 ++++++
arch/x86/kernel/module.c | 43 +++++++++++++++++++++++++++++++
include/linux/moduleloader.h | 7 +++++
kernel/livepatch/core.c | 45 +++++++++++++++++++++++++++++++++
5 files changed, 148 insertions(+)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index a93b10c48000..e461d456e447 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -741,6 +741,51 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
return 0;
}
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me)
+{
+ unsigned int i;
+ Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
+ Elf64_Sym *sym;
+ unsigned long *location;
+ const char *symname;
+ u32 *instruction;
+
+ pr_debug("Applying ADD relocate section %u to %u\n", relsec,
+ sechdrs[relsec].sh_info);
+
+ for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
+ location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ + rela[i].r_offset;
+ sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
+ + ELF64_R_SYM(rela[i].r_info);
+ symname = me->core_kallsyms.strtab
+ + sym->st_name;
+
+ if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24)
+ continue;
+
+ if (sym->st_shndx != SHN_UNDEF &&
+ sym->st_shndx != SHN_LIVEPATCH)
+ continue;
+
+ instruction = (u32 *)location;
+ if (is_mprofile_mcount_callsite(symname, instruction))
+ continue;
+
+ if (!instr_is_relative_link_branch(*instruction))
+ continue;
+
+ instruction += 1;
+ *instruction = PPC_INST_NOP;
+ }
+}
+#endif
+
#ifdef CONFIG_DYNAMIC_FTRACE
#ifdef CONFIG_MPROFILE_KERNEL
diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
index 31889db609e9..56867d052010 100644
--- a/arch/s390/kernel/module.c
+++ b/arch/s390/kernel/module.c
@@ -437,6 +437,14 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
return 0;
}
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs, const char *strtab,
+ unsigned int symindex, unsigned int relsec,
+ struct module *me)
+{
+}
+#endif
+
int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *me)
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index d5c72cb877b3..b07d71f125e6 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -215,6 +215,49 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
me->name);
return -ENOEXEC;
}
+
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me)
+{
+ unsigned int i;
+ Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
+ void *loc;
+
+ DEBUGP("Clearing relocate section %u to %u\n",
+ relsec, sechdrs[relsec].sh_info);
+ for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
+ loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ + rel[i].r_offset;
+
+ switch (ELF64_R_TYPE(rel[i].r_info)) {
+ case R_X86_64_NONE:
+ break;
+ case R_X86_64_64:
+ *(u64 *)loc = 0;
+ break;
+ case R_X86_64_32:
+ *(u32 *)loc = 0;
+ break;
+ case R_X86_64_32S:
+ *(s32 *)loc = 0;
+ break;
+ case R_X86_64_PC32:
+ case R_X86_64_PLT32:
+ *(u32 *)loc = 0;
+ break;
+ case R_X86_64_PC64:
+ *(u64 *)loc = 0;
+ break;
+ default:
+ break;
+ }
+ }
+}
+#endif
#endif
int module_finalize(const Elf_Ehdr *hdr,
diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
index 31013c2effd3..f1e52692db5f 100644
--- a/include/linux/moduleloader.h
+++ b/include/linux/moduleloader.h
@@ -62,6 +62,13 @@ int apply_relocate_add(Elf_Shdr *sechdrs,
unsigned int symindex,
unsigned int relsec,
struct module *mod);
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me);
+#endif
#else
static inline int apply_relocate_add(Elf_Shdr *sechdrs,
const char *strtab,
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index ab4a4606d19b..f0b380d2a17a 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -295,6 +295,45 @@ static int klp_write_object_relocations(struct module *pmod,
return ret;
}
+static void klp_clear_object_relocations(struct module *pmod,
+ struct klp_object *obj)
+{
+ int i, cnt;
+ const char *objname, *secname;
+ char sec_objname[MODULE_NAME_LEN];
+ Elf_Shdr *sec;
+
+ objname = klp_is_module(obj) ? obj->name : "vmlinux";
+
+ /* For each klp relocation section */
+ for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
+ sec = pmod->klp_info->sechdrs + i;
+ secname = pmod->klp_info->secstrings + sec->sh_name;
+ if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
+ continue;
+
+ /*
+ * Format: .klp.rela.sec_objname.section_name
+ * See comment in klp_resolve_symbols() for an explanation
+ * of the selected field width value.
+ */
+ secname = pmod->klp_info->secstrings + sec->sh_name;
+ cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
+ if (cnt != 1) {
+ pr_err("section %s has an incorrectly formatted name\n",
+ secname);
+ continue;
+ }
+
+ if (strcmp(objname, sec_objname))
+ continue;
+
+ clear_relocate_add(pmod->klp_info->sechdrs,
+ pmod->core_kallsyms.strtab,
+ pmod->klp_info->symndx, i, pmod);
+ }
+}
+
/*
* Sysfs Interface
*
@@ -1100,6 +1139,12 @@ static void klp_cleanup_module_patches_limited(struct module *mod,
klp_post_unpatch_callback(obj);
+ mutex_lock(&text_mutex);
+ module_disable_ro(patch->mod);
+ klp_clear_object_relocations(patch->mod, obj);
+ module_enable_ro(patch->mod, true);
+ mutex_unlock(&text_mutex);
+
klp_free_object_loaded(obj);
break;
}
--
2.23.0
On Thu 2019-09-05 14:45:12, Miroslav Benes wrote:
> We thus decided to reverse the relocation patching (clear all relocation
> targets on x86_64, or return back nops on powerpc). The solution is not
> universal and is too much arch-specific, but it may prove to be simpler
> in the end.
>
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index a93b10c48000..e461d456e447 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -741,6 +741,51 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> return 0;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +void clear_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + unsigned int i;
> + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
> + Elf64_Sym *sym;
> + unsigned long *location;
> + const char *symname;
> + u32 *instruction;
> +
> + pr_debug("Applying ADD relocate section %u to %u\n", relsec,
s/Applying/Clearing/
> + sechdrs[relsec].sh_info);
> +
> + for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
> + location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
> + + rela[i].r_offset;
> + sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
> + + ELF64_R_SYM(rela[i].r_info);
> + symname = me->core_kallsyms.strtab
> + + sym->st_name;
> +
> + if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24)
> + continue;
I expected that the code below would reverse the operations
in apply_relocate_add() for case R_PPC_REL24. But it is not
obvious for me.
It might be because I am not familiar with the code. Or would
it deserve some comments?
> +
> + if (sym->st_shndx != SHN_UNDEF &&
> + sym->st_shndx != SHN_LIVEPATCH)
> + continue;
> +
> + instruction = (u32 *)location;
> + if (is_mprofile_mcount_callsite(symname, instruction))
> + continue;
> +
> + if (!instr_is_relative_link_branch(*instruction))
> + continue;
> +
> + instruction += 1;
> + *instruction = PPC_INST_NOP;
> + }
> +}
> +#endif
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
>
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index ab4a4606d19b..f0b380d2a17a 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -295,6 +295,45 @@ static int klp_write_object_relocations(struct module *pmod,
> return ret;
> }
>
> +static void klp_clear_object_relocations(struct module *pmod,
> + struct klp_object *obj)
> +{
> + int i, cnt;
> + const char *objname, *secname;
> + char sec_objname[MODULE_NAME_LEN];
> + Elf_Shdr *sec;
> +
> + objname = klp_is_module(obj) ? obj->name : "vmlinux";
> +
> + /* For each klp relocation section */
> + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
> + sec = pmod->klp_info->sechdrs + i;
> + secname = pmod->klp_info->secstrings + sec->sh_name;
> + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> + continue;
> +
> + /*
> + * Format: .klp.rela.sec_objname.section_name
> + * See comment in klp_resolve_symbols() for an explanation
> + * of the selected field width value.
> + */
> + secname = pmod->klp_info->secstrings + sec->sh_name;
> + cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
> + if (cnt != 1) {
> + pr_err("section %s has an incorrectly formatted name\n",
> + secname);
> + continue;
> + }
> +
> + if (strcmp(objname, sec_objname))
> + continue;
> +
It would make the review easier when the order of 1st and 2nd
patch was swaped. I mean that I would not need to check twice
that the two functions actually share the same code.
> + clear_relocate_add(pmod->klp_info->sechdrs,
> + pmod->core_kallsyms.strtab,
> + pmod->klp_info->symndx, i, pmod);
> + }
> +}
> +
> /*
> * Sysfs Interface
> *
I was not able to check correctness of the ppc and s390 parts.
Otherwise, it looks good to me.
Best Regards,
Petr
On Thu, Sep 05, 2019 at 02:45:12PM +0200, Miroslav Benes wrote:
> 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.
>
> On ppc64le, we have a similar issue:
>
> module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
> livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
> livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
>
> He also proposed three different solutions. We could remove the error
> check in apply_relocate_add() introduced by commit eda9cec4c9a1
> ("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, or return back nops on powerpc). 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 <[email protected]>
> Signed-off-by: Miroslav Benes <[email protected]>
Since we decided to fix late module patching at LPC, the commit message
and clear_relocate_add() should both probably clarify that these
functions are hacks which are relatively temporary, until we fix the
root cause.
But this patch gives me a bad feeling :-/ Not that I have a better
idea.
Has anybody seen this problem in the real world? If not, maybe we'd be
better off just pretending the problem doesn't exist for now.
--
Josh
On Wed, 2 Oct 2019, Petr Mladek wrote:
> On Thu 2019-09-05 14:45:12, Miroslav Benes wrote:
> > We thus decided to reverse the relocation patching (clear all relocation
> > targets on x86_64, or return back nops on powerpc). The solution is not
> > universal and is too much arch-specific, but it may prove to be simpler
> > in the end.
> >
> > diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> > index a93b10c48000..e461d456e447 100644
> > --- a/arch/powerpc/kernel/module_64.c
> > +++ b/arch/powerpc/kernel/module_64.c
> > @@ -741,6 +741,51 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> > return 0;
> > }
> >
> > +#ifdef CONFIG_LIVEPATCH
> > +void clear_relocate_add(Elf64_Shdr *sechdrs,
> > + const char *strtab,
> > + unsigned int symindex,
> > + unsigned int relsec,
> > + struct module *me)
> > +{
> > + unsigned int i;
> > + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
> > + Elf64_Sym *sym;
> > + unsigned long *location;
> > + const char *symname;
> > + u32 *instruction;
> > +
> > + pr_debug("Applying ADD relocate section %u to %u\n", relsec,
>
> s/Applying/Clearing/
Ugh. Thanks for noticing.
> > + sechdrs[relsec].sh_info);
> > +
> > + for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
> > + location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
> > + + rela[i].r_offset;
> > + sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
> > + + ELF64_R_SYM(rela[i].r_info);
> > + symname = me->core_kallsyms.strtab
> > + + sym->st_name;
> > +
> > + if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24)
> > + continue;
>
> I expected that the code below would reverse the operations
> in apply_relocate_add() for case R_PPC_REL24. But it is not
> obvious for me.
It should, but it is not obvious. See restore_r2(). We only need to
replace PPC_INST_LD_TOC instruction with PPC_INST_NOP and that's it.
> It might be because I am not familiar with the code. Or would
> it deserve some comments?
Maybe.
> > +
> > + if (sym->st_shndx != SHN_UNDEF &&
> > + sym->st_shndx != SHN_LIVEPATCH)
> > + continue;
> > +
> > + instruction = (u32 *)location;
> > + if (is_mprofile_mcount_callsite(symname, instruction))
> > + continue;
> > +
> > + if (!instr_is_relative_link_branch(*instruction))
> > + continue;
> > +
> > + instruction += 1;
> > + *instruction = PPC_INST_NOP;
> > + }
> > +}
> > +#endif
> > +
> > #ifdef CONFIG_DYNAMIC_FTRACE
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index ab4a4606d19b..f0b380d2a17a 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -295,6 +295,45 @@ static int klp_write_object_relocations(struct module *pmod,
> > return ret;
> > }
> >
> > +static void klp_clear_object_relocations(struct module *pmod,
> > + struct klp_object *obj)
> > +{
> > + int i, cnt;
> > + const char *objname, *secname;
> > + char sec_objname[MODULE_NAME_LEN];
> > + Elf_Shdr *sec;
> > +
> > + objname = klp_is_module(obj) ? obj->name : "vmlinux";
> > +
> > + /* For each klp relocation section */
> > + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
> > + sec = pmod->klp_info->sechdrs + i;
> > + secname = pmod->klp_info->secstrings + sec->sh_name;
> > + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> > + continue;
> > +
> > + /*
> > + * Format: .klp.rela.sec_objname.section_name
> > + * See comment in klp_resolve_symbols() for an explanation
> > + * of the selected field width value.
> > + */
> > + secname = pmod->klp_info->secstrings + sec->sh_name;
> > + cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
> > + if (cnt != 1) {
> > + pr_err("section %s has an incorrectly formatted name\n",
> > + secname);
> > + continue;
> > + }
> > +
> > + if (strcmp(objname, sec_objname))
> > + continue;
> > +
>
> It would make the review easier when the order of 1st and 2nd
> patch was swaped. I mean that I would not need to check twice
> that the two functions actually share the same code.
Ok.
> > + clear_relocate_add(pmod->klp_info->sechdrs,
> > + pmod->core_kallsyms.strtab,
> > + pmod->klp_info->symndx, i, pmod);
> > + }
> > +}
> > +
> > /*
> > * Sysfs Interface
> > *
>
> I was not able to check correctness of the ppc and s390 parts.
> Otherwise, it looks good to me.
Thanks
Miroslav
On Wed, 2 Oct 2019, Josh Poimboeuf wrote:
> On Thu, Sep 05, 2019 at 02:45:12PM +0200, Miroslav Benes wrote:
> > 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.
> >
> > On ppc64le, we have a similar issue:
> >
> > module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
> > livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
> > livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
> >
> > He also proposed three different solutions. We could remove the error
> > check in apply_relocate_add() introduced by commit eda9cec4c9a1
> > ("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, or return back nops on powerpc). 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 <[email protected]>
> > Signed-off-by: Miroslav Benes <[email protected]>
>
> Since we decided to fix late module patching at LPC, the commit message
> and clear_relocate_add() should both probably clarify that these
> functions are hacks which are relatively temporary, until we fix the
> root cause.
It was the plan, but thanks for pointing it out explicitly. I could
forget.
> But this patch gives me a bad feeling :-/ Not that I have a better
> idea.
I know what you are talking about.
> Has anybody seen this problem in the real world? If not, maybe we'd be
> better off just pretending the problem doesn't exist for now.
I don't think so. You reported the issue originally and I guess it
happened during the testing. Then there is a report from Huawei, but it
suggests testing environment too. Reloading modules seems artificial to
me.
So I agree, we can pretend the issue does not exist and wait for the real
solution.
Miroslav