[PATCH] powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[PATCH] powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[Michael Ellerman]

If you build the kernel with CONFIG_RELOCATABLE=n, then install the
modules, rebuild the kernel with CONFIG_RELOCATABLE=y and leave the
old modules installed, we crash something like:

  Unable to handle kernel paging request for data at address 0xd000000018d66cef
  Faulting instruction address: 0xc0000000021ddd08
  Oops: Kernel access of bad area, sig: 11 [#1]
  Modules linked in: x_tables autofs4
  CPU: 2 PID: 1 Comm: systemd Not tainted 4.16.0-rc6-gcc_ubuntu_le-g99fec39 #1
  ...
  NIP check_version.isra.22+0x118/0x170
  Call Trace:
    __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables] (unreliable)
    resolve_symbol+0xb4/0x150
    load_module+0x10e8/0x29a0
    SyS_finit_module+0x110/0x140
    system_call+0x58/0x6c

This happens because since commit 71810db27c1c ("modversions: treat
symbol CRCs as 32 bit quantities"), a relocatable kernel encodes and
handles symbol CRCs differently from a non-relocatable kernel.

Although it's possible we could try and detect this situation and
handle it, it's much more robust to simply make the state of
CONFIG_RELOCATABLE part of the module vermagic.

Fixes: 71810db27c1c ("modversions: treat symbol CRCs as 32 bit quantities")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/include/asm/module.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index 7e28442827f1..4f6573934792 100644
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -15,9 +15,19 @@
 
 
 #ifdef CC_USING_MPROFILE_KERNEL
-#define MODULE_ARCH_VERMAGIC	"mprofile-kernel"
+#define MODULE_ARCH_VERMAGIC_FTRACE	"mprofile-kernel "
+#else
+#define MODULE_ARCH_VERMAGIC_FTRACE	""
 #endif
 
+#ifdef CONFIG_RELOCATABLE
+#define MODULE_ARCH_VERMAGIC_RELOCATABLE	"relocatable "
+#else
+#define MODULE_ARCH_VERMAGIC_RELOCATABLE	""
+#endif
+
+#define MODULE_ARCH_VERMAGIC MODULE_ARCH_VERMAGIC_FTRACE MODULE_ARCH_VERMAGIC_RELOCATABLE
+
 #ifndef __powerpc64__
 /*
  * Thanks to Paul M for explaining this.
-- 
2.14.1

Re: powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[Michael Ellerman]

On Tue, 2018-04-10 at 01:22:06 UTC, Michael Ellerman wrote:
> If you build the kernel with CONFIG_RELOCATABLE=n, then install the
> modules, rebuild the kernel with CONFIG_RELOCATABLE=y and leave the
> old modules installed, we crash something like:
> 
>   Unable to handle kernel paging request for data at address 0xd000000018d66cef
>   Faulting instruction address: 0xc0000000021ddd08
>   Oops: Kernel access of bad area, sig: 11 [#1]
>   Modules linked in: x_tables autofs4
>   CPU: 2 PID: 1 Comm: systemd Not tainted 4.16.0-rc6-gcc_ubuntu_le-g99fec39 #1
>   ...
>   NIP check_version.isra.22+0x118/0x170
>   Call Trace:
>     __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables] (unreliable)
>     resolve_symbol+0xb4/0x150
>     load_module+0x10e8/0x29a0
>     SyS_finit_module+0x110/0x140
>     system_call+0x58/0x6c
> 
> This happens because since commit 71810db27c1c ("modversions: treat
> symbol CRCs as 32 bit quantities"), a relocatable kernel encodes and
> handles symbol CRCs differently from a non-relocatable kernel.
> 
> Although it's possible we could try and detect this situation and
> handle it, it's much more robust to simply make the state of
> CONFIG_RELOCATABLE part of the module vermagic.
> 
> Fixes: 71810db27c1c ("modversions: treat symbol CRCs as 32 bit quantities")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/73aca179d78eaa11604ba0783a6d8b

cheers

Re: powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[Ard Biesheuvel]

On 11 April 2018 at 16:49, Michael Ellerman
<patch-notifications@ellerman.id.au> wrote:
> On Tue, 2018-04-10 at 01:22:06 UTC, Michael Ellerman wrote:
>> If you build the kernel with CONFIG_RELOCATABLE=n, then install the
>> modules, rebuild the kernel with CONFIG_RELOCATABLE=y and leave the
>> old modules installed, we crash something like:
>>
>>   Unable to handle kernel paging request for data at address 0xd000000018d66cef
>>   Faulting instruction address: 0xc0000000021ddd08
>>   Oops: Kernel access of bad area, sig: 11 [#1]
>>   Modules linked in: x_tables autofs4
>>   CPU: 2 PID: 1 Comm: systemd Not tainted 4.16.0-rc6-gcc_ubuntu_le-g99fec39 #1
>>   ...
>>   NIP check_version.isra.22+0x118/0x170
>>   Call Trace:
>>     __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables] (unreliable)
>>     resolve_symbol+0xb4/0x150
>>     load_module+0x10e8/0x29a0
>>     SyS_finit_module+0x110/0x140
>>     system_call+0x58/0x6c
>>
>> This happens because since commit 71810db27c1c ("modversions: treat
>> symbol CRCs as 32 bit quantities"), a relocatable kernel encodes and
>> handles symbol CRCs differently from a non-relocatable kernel.
>>
>> Although it's possible we could try and detect this situation and
>> handle it, it's much more robust to simply make the state of
>> CONFIG_RELOCATABLE part of the module vermagic.
>>
>> Fixes: 71810db27c1c ("modversions: treat symbol CRCs as 32 bit quantities")
>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>
> Applied to powerpc fixes.
>
> https://git.kernel.org/powerpc/c/73aca179d78eaa11604ba0783a6d8b
>
> cheers

Thanks for the cc. I guess this only affects powerpc, given that it is
the only arch that switches between CRC immediate values and CRC
offsets depending on the configuration.

Re: powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[Michael Ellerman]

Ard Biesheuvel <ard.biesheuvel@linaro.org> writes:

> On 11 April 2018 at 16:49, Michael Ellerman
> <patch-notifications@ellerman.id.au> wrote:
>> On Tue, 2018-04-10 at 01:22:06 UTC, Michael Ellerman wrote:
>>> If you build the kernel with CONFIG_RELOCATABLE=n, then install the
>>> modules, rebuild the kernel with CONFIG_RELOCATABLE=y and leave the
>>> old modules installed, we crash something like:
>>>
>>>   Unable to handle kernel paging request for data at address 0xd000000018d66cef
>>>   Faulting instruction address: 0xc0000000021ddd08
>>>   Oops: Kernel access of bad area, sig: 11 [#1]
>>>   Modules linked in: x_tables autofs4
>>>   CPU: 2 PID: 1 Comm: systemd Not tainted 4.16.0-rc6-gcc_ubuntu_le-g99fec39 #1
>>>   ...
>>>   NIP check_version.isra.22+0x118/0x170
>>>   Call Trace:
>>>     __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables] (unreliable)
>>>     resolve_symbol+0xb4/0x150
>>>     load_module+0x10e8/0x29a0
>>>     SyS_finit_module+0x110/0x140
>>>     system_call+0x58/0x6c
>>>
>>> This happens because since commit 71810db27c1c ("modversions: treat
>>> symbol CRCs as 32 bit quantities"), a relocatable kernel encodes and
>>> handles symbol CRCs differently from a non-relocatable kernel.
>>>
>>> Although it's possible we could try and detect this situation and
>>> handle it, it's much more robust to simply make the state of
>>> CONFIG_RELOCATABLE part of the module vermagic.
>>>
>>> Fixes: 71810db27c1c ("modversions: treat symbol CRCs as 32 bit quantities")
>>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>>
>> Applied to powerpc fixes.
>>
>> https://git.kernel.org/powerpc/c/73aca179d78eaa11604ba0783a6d8b
>
> Thanks for the cc. I guess this only affects powerpc, given that it is
> the only arch that switches between CRC immediate values and CRC
> offsets depending on the configuration.

No worries.

Is there any reason we shouldn't always turn on CONFIG_MODULE_REL_CRCS?
It seems to work, but I wanted to test it more before switching to that,
hence the quick fix above.


arch/um looks like it might be switching based on config, but I don't
know enough to say:

  config LD_SCRIPT_STATIC
  	bool
  	default y
  	depends on STATIC_LINK
  
  config LD_SCRIPT_DYN
  	bool
  	default y
  	depends on !LD_SCRIPT_STATIC
          select MODULE_REL_CRCS if MODVERSIONS


cheers

Re: powerpc/modules: Fix crashes by adding CONFIG_RELOCATABLE to vermagic

[Ard Biesheuvel]

On 16 April 2018 at 16:10, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Ard Biesheuvel <ard.biesheuvel@linaro.org> writes:
>
>> On 11 April 2018 at 16:49, Michael Ellerman
>> <patch-notifications@ellerman.id.au> wrote:
>>> On Tue, 2018-04-10 at 01:22:06 UTC, Michael Ellerman wrote:
>>>> If you build the kernel with CONFIG_RELOCATABLE=n, then install the
>>>> modules, rebuild the kernel with CONFIG_RELOCATABLE=y and leave the
>>>> old modules installed, we crash something like:
>>>>
>>>>   Unable to handle kernel paging request for data at address 0xd000000018d66cef
>>>>   Faulting instruction address: 0xc0000000021ddd08
>>>>   Oops: Kernel access of bad area, sig: 11 [#1]
>>>>   Modules linked in: x_tables autofs4
>>>>   CPU: 2 PID: 1 Comm: systemd Not tainted 4.16.0-rc6-gcc_ubuntu_le-g99fec39 #1
>>>>   ...
>>>>   NIP check_version.isra.22+0x118/0x170
>>>>   Call Trace:
>>>>     __ksymtab_xt_unregister_table+0x58/0xfffffffffffffcb8 [x_tables] (unreliable)
>>>>     resolve_symbol+0xb4/0x150
>>>>     load_module+0x10e8/0x29a0
>>>>     SyS_finit_module+0x110/0x140
>>>>     system_call+0x58/0x6c
>>>>
>>>> This happens because since commit 71810db27c1c ("modversions: treat
>>>> symbol CRCs as 32 bit quantities"), a relocatable kernel encodes and
>>>> handles symbol CRCs differently from a non-relocatable kernel.
>>>>
>>>> Although it's possible we could try and detect this situation and
>>>> handle it, it's much more robust to simply make the state of
>>>> CONFIG_RELOCATABLE part of the module vermagic.
>>>>
>>>> Fixes: 71810db27c1c ("modversions: treat symbol CRCs as 32 bit quantities")
>>>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>>>
>>> Applied to powerpc fixes.
>>>
>>> https://git.kernel.org/powerpc/c/73aca179d78eaa11604ba0783a6d8b
>>
>> Thanks for the cc. I guess this only affects powerpc, given that it is
>> the only arch that switches between CRC immediate values and CRC
>> offsets depending on the configuration.
>
> No worries.
>
> Is there any reason we shouldn't always turn on CONFIG_MODULE_REL_CRCS?
> It seems to work, but I wanted to test it more before switching to that,
> hence the quick fix above.
>
>
> arch/um looks like it might be switching based on config, but I don't
> know enough to say:
>
>   config LD_SCRIPT_STATIC
>         bool
>         default y
>         depends on STATIC_LINK
>
>   config LD_SCRIPT_DYN
>         bool
>         default y
>         depends on !LD_SCRIPT_STATIC
>           select MODULE_REL_CRCS if MODVERSIONS
>

The only reason not to enable it is that it ends up taking more space
on a 32-bit architecture with CONFIG_RELOCATABLE=n, given that you
need to record both the relative offset and the actual CRC value (both
32-bit quantities) rather than just the CRC itself. On a 64-bit arch
with CONFIG_RELOCATABLE=n, you end up replacing a single 64-bit
quantity with two 32-bit quantities, so it doesn't really matter.