* Re: [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal
2023-01-21 0:49 ` [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal Song Liu
@ 2023-01-24 12:24 ` Petr Mladek
2023-01-24 17:23 ` Josh Poimboeuf
2023-01-24 17:56 ` Song Liu
2023-01-25 9:58 ` Christophe Leroy
2 siblings, 1 reply; 9+ messages in thread
From: Petr Mladek @ 2023-01-24 12:24 UTC (permalink / raw)
To: Song Liu
Cc: linux-kernel, linux-modules, live-patching, x86, Josh Poimboeuf,
Miroslav Benes
On Fri 2023-01-20 16:49:45, Song Liu 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.
>
> 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). 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>
>
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
> return 0;
> }
> #else /*X86_64*/
> -static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> +static int __write_relocate_add(Elf64_Shdr *sechdrs,
> const char *strtab,
> unsigned int symindex,
> unsigned int relsec,
> struct module *me,
> - void *(*write)(void *dest, const void *src, size_t len))
> + void *(*write)(void *dest, const void *src, size_t len),
> + bool apply)
> {
> unsigned int i;
> Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> Elf64_Sym *sym;
> void *loc;
> u64 val;
> + u64 zero = 0ULL;
>
> - DEBUGP("Applying relocate section %u to %u\n",
> + DEBUGP("%s relocate section %u to %u\n",
> + apply ? "Applying" : "Clearing",
> relsec, sechdrs[relsec].sh_info);
> for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
> + int size = 0;
The value 0 should never be used. It is better to do not initialize
it at all so that the compiler would warn when the variable might be
used uninitialized.
Note that this warning is not enabled by default. It can be enabled
with
$> make W=2 arch/x86/kernel/module.o
> +
> /* This is where to make the change */
> loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
> + rel[i].r_offset;
Otherwise, it looks good.
With the removed initialization, feel free to use:
Reviewed-by: Petr Mladek <pmladek@suse.com>
Best Regards,
Petr
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal
2023-01-24 12:24 ` Petr Mladek
@ 2023-01-24 17:23 ` Josh Poimboeuf
2023-01-24 17:30 ` Song Liu
0 siblings, 1 reply; 9+ messages in thread
From: Josh Poimboeuf @ 2023-01-24 17:23 UTC (permalink / raw)
To: Petr Mladek
Cc: Song Liu, linux-kernel, linux-modules, live-patching, x86,
Josh Poimboeuf, Miroslav Benes
On Tue, Jan 24, 2023 at 01:24:15PM +0100, Petr Mladek wrote:
> On Fri 2023-01-20 16:49:45, Song Liu 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.
> >
> > 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). 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>
> >
> > --- a/arch/x86/kernel/module.c
> > +++ b/arch/x86/kernel/module.c
> > @@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
> > return 0;
> > }
> > #else /*X86_64*/
> > -static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> > +static int __write_relocate_add(Elf64_Shdr *sechdrs,
> > const char *strtab,
> > unsigned int symindex,
> > unsigned int relsec,
> > struct module *me,
> > - void *(*write)(void *dest, const void *src, size_t len))
> > + void *(*write)(void *dest, const void *src, size_t len),
> > + bool apply)
> > {
> > unsigned int i;
> > Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> > Elf64_Sym *sym;
> > void *loc;
> > u64 val;
> > + u64 zero = 0ULL;
> >
> > - DEBUGP("Applying relocate section %u to %u\n",
> > + DEBUGP("%s relocate section %u to %u\n",
> > + apply ? "Applying" : "Clearing",
> > relsec, sechdrs[relsec].sh_info);
> > for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
> > + int size = 0;
>
> The value 0 should never be used. It is better to do not initialize
> it at all so that the compiler would warn when the variable might be
> used uninitialized.
Yes. Also it can be unsigned, i.e. size_t.
--
Josh
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal
2023-01-24 17:23 ` Josh Poimboeuf
@ 2023-01-24 17:30 ` Song Liu
0 siblings, 0 replies; 9+ messages in thread
From: Song Liu @ 2023-01-24 17:30 UTC (permalink / raw)
To: Josh Poimboeuf
Cc: Petr Mladek, linux-kernel, linux-modules, live-patching, x86,
Josh Poimboeuf, Miroslav Benes
On Tue, Jan 24, 2023 at 9:23 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> On Tue, Jan 24, 2023 at 01:24:15PM +0100, Petr Mladek wrote:
> > On Fri 2023-01-20 16:49:45, Song Liu 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.
> > >
> > > 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). 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>
> > >
> > > --- a/arch/x86/kernel/module.c
> > > +++ b/arch/x86/kernel/module.c
> > > @@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
> > > return 0;
> > > }
> > > #else /*X86_64*/
> > > -static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> > > +static int __write_relocate_add(Elf64_Shdr *sechdrs,
> > > const char *strtab,
> > > unsigned int symindex,
> > > unsigned int relsec,
> > > struct module *me,
> > > - void *(*write)(void *dest, const void *src, size_t len))
> > > + void *(*write)(void *dest, const void *src, size_t len),
> > > + bool apply)
> > > {
> > > unsigned int i;
> > > Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> > > Elf64_Sym *sym;
> > > void *loc;
> > > u64 val;
> > > + u64 zero = 0ULL;
> > >
> > > - DEBUGP("Applying relocate section %u to %u\n",
> > > + DEBUGP("%s relocate section %u to %u\n",
> > > + apply ? "Applying" : "Clearing",
> > > relsec, sechdrs[relsec].sh_info);
> > > for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
> > > + int size = 0;
> >
> > The value 0 should never be used. It is better to do not initialize
> > it at all so that the compiler would warn when the variable might be
> > used uninitialized.
>
> Yes. Also it can be unsigned, i.e. size_t.
Will fix this in the next version.
I guess we still need an Acked-by from x86 maintainers.
Thanks,
Song
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal
2023-01-21 0:49 ` [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal Song Liu
2023-01-24 12:24 ` Petr Mladek
@ 2023-01-24 17:56 ` Song Liu
2023-01-25 9:58 ` Christophe Leroy
2 siblings, 0 replies; 9+ messages in thread
From: Song Liu @ 2023-01-24 17:56 UTC (permalink / raw)
To: linux-kernel, linux-modules, live-patching, Thomas Gleixner
Cc: x86, Josh Poimboeuf, Miroslav Benes
Hi Thomas,
Could you please help review this change from x86 side?
Thanks,
Song
On Fri, Jan 20, 2023 at 4:50 PM Song Liu <song@kernel.org> 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.
>
> 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). 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>
>
> ---
>
> NOTE: powerpc32 code is only compile tested.
>
> Changes v9 => v10:
> 1. Revise commit log. (Josh Poimboeuf)
> 2. Various improvements in code style, comments, etc. (Josh Poimboeuf)
>
> Changes v8 => v9:
> 1. Fix overflow check for R_X86_64_PC32 and R_X86_64_PLT32. (Petr Mladek)
>
> Changes v7 = v8:
> 1. Remove the logic in powerpc/kernel/module_64.c, as there is ongoing
> discussions.
> 2. For x86_64, add check for expected value during clear_relocate_add().
> (Petr Mladek)
> 3. Optimize the logic in klp_write_section_relocs(). (Petr Mladek)
> 4. Optimize __write_relocate_add (x86_64). (Joe Lawrence)
>
> Changes v6 = v7:
> 1. Reduce code duplication in livepatch/core.c and x86/kernel/module.c.
> 2. Add more comments to powerpc/kernel/module_64.c.
> 3. Added Joe's Tested-by (which I should have added in v6).
>
> Changes v5 = v6:
> 1. Fix powerpc64.
> 2. Fix compile for powerpc32.
>
> Changes v4 = v5:
> 1. Fix compile with powerpc.
>
> Changes v3 = v4:
> 1. Reuse __apply_relocate_add to make it more reliable in long term.
> (Josh Poimboeuf)
> 2. Add back ppc64 logic from v2, with changes to match current code.
> (Josh Poimboeuf)
>
> Changes v2 => v3:
> 1. Rewrite x86 changes to match current code style.
> 2. Remove powerpc changes as there is no test coverage in v3.
> 3. Only keep 1/3 of v2.
>
> v2: https://lore.kernel.org/all/20190905124514.8944-1-mbenes@suse.cz/T/#u
>
> fix
> ---
> arch/powerpc/kernel/module_32.c | 10 ++++
> arch/powerpc/kernel/module_64.c | 10 ++++
> arch/s390/kernel/module.c | 8 +++
> arch/x86/kernel/module.c | 93 +++++++++++++++++++++------------
> include/linux/moduleloader.h | 17 ++++++
> kernel/livepatch/core.c | 54 ++++++++++++++-----
> 6 files changed, 146 insertions(+), 46 deletions(-)
>
> diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
> index ea6536171778..e3c312770453 100644
> --- a/arch/powerpc/kernel/module_32.c
> +++ b/arch/powerpc/kernel/module_32.c
> @@ -285,6 +285,16 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
> return 0;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +void clear_relocate_add(Elf32_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> +}
> +#endif
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> notrace int module_trampoline_target(struct module *mod, unsigned long addr,
> unsigned long *target)
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index ff045644f13f..1096d6b3a62c 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -749,6 +749,16 @@ 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)
> +{
> +}
> +#endif
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> int module_trampoline_target(struct module *mod, unsigned long addr,
> unsigned long *target)
> diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
> index 2d159b32885b..cc6784fbc1ac 100644
> --- a/arch/s390/kernel/module.c
> +++ b/arch/s390/kernel/module.c
> @@ -500,6 +500,14 @@ static int module_alloc_ftrace_hotpatch_trampolines(struct module *me,
> }
> #endif /* CONFIG_FUNCTION_TRACER */
>
> +#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 1dee3ad82da2..e4aab0395a33 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
> return 0;
> }
> #else /*X86_64*/
> -static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> +static int __write_relocate_add(Elf64_Shdr *sechdrs,
> const char *strtab,
> unsigned int symindex,
> unsigned int relsec,
> struct module *me,
> - void *(*write)(void *dest, const void *src, size_t len))
> + void *(*write)(void *dest, const void *src, size_t len),
> + bool apply)
> {
> unsigned int i;
> Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> Elf64_Sym *sym;
> void *loc;
> u64 val;
> + u64 zero = 0ULL;
>
> - DEBUGP("Applying relocate section %u to %u\n",
> + DEBUGP("%s relocate section %u to %u\n",
> + apply ? "Applying" : "Clearing",
> relsec, sechdrs[relsec].sh_info);
> for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
> + int size = 0;
> +
> /* This is where to make the change */
> loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
> + rel[i].r_offset;
> @@ -162,52 +167,53 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
>
> switch (ELF64_R_TYPE(rel[i].r_info)) {
> case R_X86_64_NONE:
> - break;
> + continue; /* nothing to write */
> case R_X86_64_64:
> - if (*(u64 *)loc != 0)
> - goto invalid_relocation;
> - write(loc, &val, 8);
> + size = 8;
> break;
> case R_X86_64_32:
> - if (*(u32 *)loc != 0)
> - goto invalid_relocation;
> - write(loc, &val, 4);
> - if (val != *(u32 *)loc)
> + if (val != *(u32 *)&val)
> goto overflow;
> + size = 4;
> break;
> case R_X86_64_32S:
> - if (*(s32 *)loc != 0)
> - goto invalid_relocation;
> - write(loc, &val, 4);
> - if ((s64)val != *(s32 *)loc)
> + if ((s64)val != *(s32 *)&val)
> goto overflow;
> + size = 4;
> break;
> case R_X86_64_PC32:
> case R_X86_64_PLT32:
> - if (*(u32 *)loc != 0)
> - goto invalid_relocation;
> val -= (u64)loc;
> - write(loc, &val, 4);
> + size = 4;
> break;
> case R_X86_64_PC64:
> - if (*(u64 *)loc != 0)
> - goto invalid_relocation;
> val -= (u64)loc;
> - write(loc, &val, 8);
> + size = 8;
> break;
> default:
> pr_err("%s: Unknown rela relocation: %llu\n",
> me->name, ELF64_R_TYPE(rel[i].r_info));
> return -ENOEXEC;
> }
> +
> + if (apply) {
> + if (memcmp(loc, &zero, size)) {
> + pr_err("x86/modules: Invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
> + (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
> + return -ENOEXEC;
> + }
> + write(loc, &val, size);
> + } else {
> + if (memcmp(loc, &val, size)) {
> + pr_warn("x86/modules: Invalid relocation target, existing value does not match expected value for type %d, loc %p, val %Lx\n",
> + (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
> + return -ENOEXEC;
> + }
> + write(loc, &zero, size);
> + }
> }
> return 0;
>
> -invalid_relocation:
> - pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
> - (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
> - return -ENOEXEC;
> -
> overflow:
> pr_err("overflow in relocation type %d val %Lx\n",
> (int)ELF64_R_TYPE(rel[i].r_info), val);
> @@ -216,11 +222,12 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> return -ENOEXEC;
> }
>
> -int apply_relocate_add(Elf64_Shdr *sechdrs,
> - const char *strtab,
> - unsigned int symindex,
> - unsigned int relsec,
> - struct module *me)
> +static int write_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me,
> + bool apply)
> {
> int ret;
> bool early = me->state == MODULE_STATE_UNFORMED;
> @@ -231,8 +238,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> mutex_lock(&text_mutex);
> }
>
> - ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
> - write);
> + ret = __write_relocate_add(sechdrs, strtab, symindex, relsec, me,
> + write, apply);
>
> if (!early) {
> text_poke_sync();
> @@ -242,6 +249,26 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> return ret;
> }
>
> +int apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + return write_relocate_add(sechdrs, strtab, symindex, relsec, me, true);
> +}
> +
> +#ifdef CONFIG_LIVEPATCH
> +void clear_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + write_relocate_add(sechdrs, strtab, symindex, relsec, me, false);
> +}
> +#endif
> +
> #endif
>
> int module_finalize(const Elf_Ehdr *hdr,
> diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
> index 7b4587a19189..03be088fb439 100644
> --- a/include/linux/moduleloader.h
> +++ b/include/linux/moduleloader.h
> @@ -75,6 +75,23 @@ int apply_relocate_add(Elf_Shdr *sechdrs,
> unsigned int symindex,
> unsigned int relsec,
> struct module *mod);
> +#ifdef CONFIG_LIVEPATCH
> +/*
> + * Some architectures (namely x86_64 and ppc64) perform sanity checks when
> + * applying relocations. If a patched module gets unloaded and then later
> + * reloaded (and re-patched), klp re-applies relocations to the replacement
> + * function(s). Any leftover relocations from the previous loading of the
> + * patched module might trigger the sanity checks.
> + *
> + * To prevent that, when unloading a patched module, clear out any relocations
> + * that might trigger arch-specific sanity checks on a future module reload.
> + */
> +void clear_relocate_add(Elf_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 201f0c0482fb..c72f378181ce 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -291,10 +291,10 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
> * the to-be-patched module to be loaded and patched sometime *after* the
> * klp module is loaded.
> */
> -int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> - const char *shstrtab, const char *strtab,
> - unsigned int symndx, unsigned int secndx,
> - const char *objname)
> +static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> + const char *shstrtab, const char *strtab,
> + unsigned int symndx, unsigned int secndx,
> + const char *objname, bool apply)
> {
> int cnt, ret;
> char sec_objname[MODULE_NAME_LEN];
> @@ -316,11 +316,26 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> if (strcmp(objname ? objname : "vmlinux", sec_objname))
> return 0;
>
> - ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname);
> - if (ret)
> - return ret;
> + if (apply) {
> + ret = klp_resolve_symbols(sechdrs, strtab, symndx,
> + sec, sec_objname);
> + if (ret)
> + return ret;
>
> - return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> + return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> + }
> +
> + clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> + return 0;
> +}
> +
> +int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> + const char *shstrtab, const char *strtab,
> + unsigned int symndx, unsigned int secndx,
> + const char *objname)
> +{
> + return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx,
> + secndx, objname, true);
> }
>
> /*
> @@ -769,8 +784,9 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
> func->old_sympos ? func->old_sympos : 1);
> }
>
> -static int klp_apply_object_relocs(struct klp_patch *patch,
> - struct klp_object *obj)
> +static int klp_write_object_relocs(struct klp_patch *patch,
> + struct klp_object *obj,
> + bool apply)
> {
> int i, ret;
> struct klp_modinfo *info = patch->mod->klp_info;
> @@ -781,10 +797,10 @@ static int klp_apply_object_relocs(struct klp_patch *patch,
> if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> continue;
>
> - ret = klp_apply_section_relocs(patch->mod, info->sechdrs,
> + ret = klp_write_section_relocs(patch->mod, info->sechdrs,
> info->secstrings,
> patch->mod->core_kallsyms.strtab,
> - info->symndx, i, obj->name);
> + info->symndx, i, obj->name, apply);
> if (ret)
> return ret;
> }
> @@ -792,6 +808,18 @@ static int klp_apply_object_relocs(struct klp_patch *patch,
> return 0;
> }
>
> +static int klp_apply_object_relocs(struct klp_patch *patch,
> + struct klp_object *obj)
> +{
> + return klp_write_object_relocs(patch, obj, true);
> +}
> +
> +static void klp_clear_object_relocs(struct klp_patch *patch,
> + struct klp_object *obj)
> +{
> + klp_write_object_relocs(patch, obj, false);
> +}
> +
> /* parts of the initialization that is done only when the object is loaded */
> static int klp_init_object_loaded(struct klp_patch *patch,
> struct klp_object *obj)
> @@ -1179,7 +1207,7 @@ static void klp_cleanup_module_patches_limited(struct module *mod,
> klp_unpatch_object(obj);
>
> klp_post_unpatch_callback(obj);
> -
> + klp_clear_object_relocs(patch, obj);
> klp_free_object_loaded(obj);
> break;
> }
> --
> 2.30.2
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal
2023-01-21 0:49 ` [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal Song Liu
2023-01-24 12:24 ` Petr Mladek
2023-01-24 17:56 ` Song Liu
@ 2023-01-25 9:58 ` Christophe Leroy
2023-01-25 17:14 ` Song Liu
2 siblings, 1 reply; 9+ messages in thread
From: Christophe Leroy @ 2023-01-25 9:58 UTC (permalink / raw)
To: Song Liu, linux-kernel, linux-modules, live-patching
Cc: x86, Josh Poimboeuf, Miroslav Benes
Le 21/01/2023 à 01:49, Song Liu a écrit :
> 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 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). The solution is not
> universal and is too much arch-specific, but it may prove to be simpler
> in the end.
Would it be possible to not add empty clear_relocate_add() on all
architecture while only x86 implements it ? Can we make it an empty
static inline in generic livepatch.h for the architectures not
implementing it, like we do for most mm functions ?
Another solution would be to define an empty generic weak version of
clear_relocate_add()
Christophe
>
> 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>
>
> ---
>
> NOTE: powerpc32 code is only compile tested.
>
> Changes v9 => v10:
> 1. Revise commit log. (Josh Poimboeuf)
> 2. Various improvements in code style, comments, etc. (Josh Poimboeuf)
>
> Changes v8 => v9:
> 1. Fix overflow check for R_X86_64_PC32 and R_X86_64_PLT32. (Petr Mladek)
>
> Changes v7 = v8:
> 1. Remove the logic in powerpc/kernel/module_64.c, as there is ongoing
> discussions.
> 2. For x86_64, add check for expected value during clear_relocate_add().
> (Petr Mladek)
> 3. Optimize the logic in klp_write_section_relocs(). (Petr Mladek)
> 4. Optimize __write_relocate_add (x86_64). (Joe Lawrence)
>
> Changes v6 = v7:
> 1. Reduce code duplication in livepatch/core.c and x86/kernel/module.c.
> 2. Add more comments to powerpc/kernel/module_64.c.
> 3. Added Joe's Tested-by (which I should have added in v6).
>
> Changes v5 = v6:
> 1. Fix powerpc64.
> 2. Fix compile for powerpc32.
>
> Changes v4 = v5:
> 1. Fix compile with powerpc.
>
> Changes v3 = v4:
> 1. Reuse __apply_relocate_add to make it more reliable in long term.
> (Josh Poimboeuf)
> 2. Add back ppc64 logic from v2, with changes to match current code.
> (Josh Poimboeuf)
>
> Changes v2 => v3:
> 1. Rewrite x86 changes to match current code style.
> 2. Remove powerpc changes as there is no test coverage in v3.
> 3. Only keep 1/3 of v2.
>
> v2: https://lore.kernel.org/all/20190905124514.8944-1-mbenes@suse.cz/T/#u
>
> fix
> ---
> arch/powerpc/kernel/module_32.c | 10 ++++
> arch/powerpc/kernel/module_64.c | 10 ++++
> arch/s390/kernel/module.c | 8 +++
> arch/x86/kernel/module.c | 93 +++++++++++++++++++++------------
> include/linux/moduleloader.h | 17 ++++++
> kernel/livepatch/core.c | 54 ++++++++++++++-----
> 6 files changed, 146 insertions(+), 46 deletions(-)
>
> diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
> index ea6536171778..e3c312770453 100644
> --- a/arch/powerpc/kernel/module_32.c
> +++ b/arch/powerpc/kernel/module_32.c
> @@ -285,6 +285,16 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
> return 0;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +void clear_relocate_add(Elf32_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> +}
> +#endif
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> notrace int module_trampoline_target(struct module *mod, unsigned long addr,
> unsigned long *target)
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index ff045644f13f..1096d6b3a62c 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -749,6 +749,16 @@ 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)
> +{
> +}
> +#endif
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> int module_trampoline_target(struct module *mod, unsigned long addr,
> unsigned long *target)
> diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
> index 2d159b32885b..cc6784fbc1ac 100644
> --- a/arch/s390/kernel/module.c
> +++ b/arch/s390/kernel/module.c
> @@ -500,6 +500,14 @@ static int module_alloc_ftrace_hotpatch_trampolines(struct module *me,
> }
> #endif /* CONFIG_FUNCTION_TRACER */
>
> +#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 1dee3ad82da2..e4aab0395a33 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -129,22 +129,27 @@ int apply_relocate(Elf32_Shdr *sechdrs,
> return 0;
> }
> #else /*X86_64*/
> -static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> +static int __write_relocate_add(Elf64_Shdr *sechdrs,
> const char *strtab,
> unsigned int symindex,
> unsigned int relsec,
> struct module *me,
> - void *(*write)(void *dest, const void *src, size_t len))
> + void *(*write)(void *dest, const void *src, size_t len),
> + bool apply)
> {
> unsigned int i;
> Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> Elf64_Sym *sym;
> void *loc;
> u64 val;
> + u64 zero = 0ULL;
>
> - DEBUGP("Applying relocate section %u to %u\n",
> + DEBUGP("%s relocate section %u to %u\n",
> + apply ? "Applying" : "Clearing",
> relsec, sechdrs[relsec].sh_info);
> for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
> + int size = 0;
> +
> /* This is where to make the change */
> loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
> + rel[i].r_offset;
> @@ -162,52 +167,53 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
>
> switch (ELF64_R_TYPE(rel[i].r_info)) {
> case R_X86_64_NONE:
> - break;
> + continue; /* nothing to write */
> case R_X86_64_64:
> - if (*(u64 *)loc != 0)
> - goto invalid_relocation;
> - write(loc, &val, 8);
> + size = 8;
> break;
> case R_X86_64_32:
> - if (*(u32 *)loc != 0)
> - goto invalid_relocation;
> - write(loc, &val, 4);
> - if (val != *(u32 *)loc)
> + if (val != *(u32 *)&val)
> goto overflow;
> + size = 4;
> break;
> case R_X86_64_32S:
> - if (*(s32 *)loc != 0)
> - goto invalid_relocation;
> - write(loc, &val, 4);
> - if ((s64)val != *(s32 *)loc)
> + if ((s64)val != *(s32 *)&val)
> goto overflow;
> + size = 4;
> break;
> case R_X86_64_PC32:
> case R_X86_64_PLT32:
> - if (*(u32 *)loc != 0)
> - goto invalid_relocation;
> val -= (u64)loc;
> - write(loc, &val, 4);
> + size = 4;
> break;
> case R_X86_64_PC64:
> - if (*(u64 *)loc != 0)
> - goto invalid_relocation;
> val -= (u64)loc;
> - write(loc, &val, 8);
> + size = 8;
> break;
> default:
> pr_err("%s: Unknown rela relocation: %llu\n",
> me->name, ELF64_R_TYPE(rel[i].r_info));
> return -ENOEXEC;
> }
> +
> + if (apply) {
> + if (memcmp(loc, &zero, size)) {
> + pr_err("x86/modules: Invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
> + (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
> + return -ENOEXEC;
> + }
> + write(loc, &val, size);
> + } else {
> + if (memcmp(loc, &val, size)) {
> + pr_warn("x86/modules: Invalid relocation target, existing value does not match expected value for type %d, loc %p, val %Lx\n",
> + (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
> + return -ENOEXEC;
> + }
> + write(loc, &zero, size);
> + }
> }
> return 0;
>
> -invalid_relocation:
> - pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
> - (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
> - return -ENOEXEC;
> -
> overflow:
> pr_err("overflow in relocation type %d val %Lx\n",
> (int)ELF64_R_TYPE(rel[i].r_info), val);
> @@ -216,11 +222,12 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> return -ENOEXEC;
> }
>
> -int apply_relocate_add(Elf64_Shdr *sechdrs,
> - const char *strtab,
> - unsigned int symindex,
> - unsigned int relsec,
> - struct module *me)
> +static int write_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me,
> + bool apply)
> {
> int ret;
> bool early = me->state == MODULE_STATE_UNFORMED;
> @@ -231,8 +238,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> mutex_lock(&text_mutex);
> }
>
> - ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
> - write);
> + ret = __write_relocate_add(sechdrs, strtab, symindex, relsec, me,
> + write, apply);
>
> if (!early) {
> text_poke_sync();
> @@ -242,6 +249,26 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> return ret;
> }
>
> +int apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + return write_relocate_add(sechdrs, strtab, symindex, relsec, me, true);
> +}
> +
> +#ifdef CONFIG_LIVEPATCH
> +void clear_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + write_relocate_add(sechdrs, strtab, symindex, relsec, me, false);
> +}
> +#endif
> +
> #endif
>
> int module_finalize(const Elf_Ehdr *hdr,
> diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
> index 7b4587a19189..03be088fb439 100644
> --- a/include/linux/moduleloader.h
> +++ b/include/linux/moduleloader.h
> @@ -75,6 +75,23 @@ int apply_relocate_add(Elf_Shdr *sechdrs,
> unsigned int symindex,
> unsigned int relsec,
> struct module *mod);
> +#ifdef CONFIG_LIVEPATCH
> +/*
> + * Some architectures (namely x86_64 and ppc64) perform sanity checks when
> + * applying relocations. If a patched module gets unloaded and then later
> + * reloaded (and re-patched), klp re-applies relocations to the replacement
> + * function(s). Any leftover relocations from the previous loading of the
> + * patched module might trigger the sanity checks.
> + *
> + * To prevent that, when unloading a patched module, clear out any relocations
> + * that might trigger arch-specific sanity checks on a future module reload.
> + */
> +void clear_relocate_add(Elf_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 201f0c0482fb..c72f378181ce 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -291,10 +291,10 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
> * the to-be-patched module to be loaded and patched sometime *after* the
> * klp module is loaded.
> */
> -int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> - const char *shstrtab, const char *strtab,
> - unsigned int symndx, unsigned int secndx,
> - const char *objname)
> +static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> + const char *shstrtab, const char *strtab,
> + unsigned int symndx, unsigned int secndx,
> + const char *objname, bool apply)
> {
> int cnt, ret;
> char sec_objname[MODULE_NAME_LEN];
> @@ -316,11 +316,26 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> if (strcmp(objname ? objname : "vmlinux", sec_objname))
> return 0;
>
> - ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname);
> - if (ret)
> - return ret;
> + if (apply) {
> + ret = klp_resolve_symbols(sechdrs, strtab, symndx,
> + sec, sec_objname);
> + if (ret)
> + return ret;
>
> - return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> + return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> + }
> +
> + clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> + return 0;
> +}
> +
> +int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> + const char *shstrtab, const char *strtab,
> + unsigned int symndx, unsigned int secndx,
> + const char *objname)
> +{
> + return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx,
> + secndx, objname, true);
> }
>
> /*
> @@ -769,8 +784,9 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
> func->old_sympos ? func->old_sympos : 1);
> }
>
> -static int klp_apply_object_relocs(struct klp_patch *patch,
> - struct klp_object *obj)
> +static int klp_write_object_relocs(struct klp_patch *patch,
> + struct klp_object *obj,
> + bool apply)
> {
> int i, ret;
> struct klp_modinfo *info = patch->mod->klp_info;
> @@ -781,10 +797,10 @@ static int klp_apply_object_relocs(struct klp_patch *patch,
> if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> continue;
>
> - ret = klp_apply_section_relocs(patch->mod, info->sechdrs,
> + ret = klp_write_section_relocs(patch->mod, info->sechdrs,
> info->secstrings,
> patch->mod->core_kallsyms.strtab,
> - info->symndx, i, obj->name);
> + info->symndx, i, obj->name, apply);
> if (ret)
> return ret;
> }
> @@ -792,6 +808,18 @@ static int klp_apply_object_relocs(struct klp_patch *patch,
> return 0;
> }
>
> +static int klp_apply_object_relocs(struct klp_patch *patch,
> + struct klp_object *obj)
> +{
> + return klp_write_object_relocs(patch, obj, true);
> +}
> +
> +static void klp_clear_object_relocs(struct klp_patch *patch,
> + struct klp_object *obj)
> +{
> + klp_write_object_relocs(patch, obj, false);
> +}
> +
> /* parts of the initialization that is done only when the object is loaded */
> static int klp_init_object_loaded(struct klp_patch *patch,
> struct klp_object *obj)
> @@ -1179,7 +1207,7 @@ static void klp_cleanup_module_patches_limited(struct module *mod,
> klp_unpatch_object(obj);
>
> klp_post_unpatch_callback(obj);
> -
> + klp_clear_object_relocs(patch, obj);
> klp_free_object_loaded(obj);
> break;
> }
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v10 2/2] livepatch,x86: Clear relocation targets on a module removal
2023-01-25 9:58 ` Christophe Leroy
@ 2023-01-25 17:14 ` Song Liu
0 siblings, 0 replies; 9+ messages in thread
From: Song Liu @ 2023-01-25 17:14 UTC (permalink / raw)
To: Christophe Leroy
Cc: linux-kernel, linux-modules, live-patching, x86, Josh Poimboeuf,
Miroslav Benes
On Wed, Jan 25, 2023 at 1:58 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 21/01/2023 à 01:49, Song Liu a écrit :
> > 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 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). The solution is not
> > universal and is too much arch-specific, but it may prove to be simpler
> > in the end.
>
> Would it be possible to not add empty clear_relocate_add() on all
> architecture while only x86 implements it ? Can we make it an empty
> static inline in generic livepatch.h for the architectures not
> implementing it, like we do for most mm functions ?
>
> Another solution would be to define an empty generic weak version of
> clear_relocate_add()
Sure, I will replace these with a week function.
Thanks,
Song
^ permalink raw reply [flat|nested] 9+ messages in thread