2019-06-07 12:59:40

by Matthias Schiffer

Subject: [PATCH modules v2 0/2] Fix handling of exit unwinding sections (on ARM)

For some time (050d18d1c651 "ARM: 8650/1: module: handle negative
R_ARM_PREL31 addends correctly", v4.11+), building a kernel without
CONFIG_MODULE_UNLOAD would lead to module loads failing on ARM systems with
certain memory layouts, with messages like:

imx_sdma: section 16 reloc 0 sym '': relocation 42 out of range
(0x7f015260 -> 0xc0f5a5e8)

(0x7f015260 is in the module load area, 0xc0f5a5e8 a regular vmalloc
address; relocation 42 is R_ARM_PREL31)

This is caused by relocatiosn in the .ARM.extab.exit.text and
.ARM.exidx.exit.text sections referencing the .exit.text section. As the
module loader will omit loading .exit.text without CONFIG_MODULE_UNLOAD,
there will be relocations from loaded to unloaded sections; the resulting
huge offsets trigger the sanity checks added in 050d18d1c651.

IA64 might be affected by a similar issue - sections with names like
.IA_64.unwind.exit.text and .IA_64.unwind_info.exit.text appear in the ld
script - but I don't know much about that arch.

Also, I'm not sure if this is stable-worthy - just enabling
CONFIG_MODULE_UNLOAD should be a viable workaround on affected kernels.

v2: Use __weak function as suggested by Jessica


Matthias Schiffer (2):
module: allow arch overrides for .exit section names
ARM: module: recognize unwind exit sections

arch/arm/kernel/module.c | 7 +++++++
include/linux/moduleloader.h | 5 +++++
kernel/module.c | 7 ++++++-
3 files changed, 18 insertions(+), 1 deletion(-)

--
2.17.1

2019-06-21 12:36:05

by Matthias Schiffer

Subject: Re: [PATCH modules v2 0/2] Fix handling of exit unwinding sections (on ARM)

On Fri, 2019-06-07 at 12:49 +0200, Matthias Schiffer wrote:
> For some time (050d18d1c651 "ARM: 8650/1: module: handle negative
> R_ARM_PREL31 addends correctly", v4.11+), building a kernel without
> CONFIG_MODULE_UNLOAD would lead to module loads failing on ARM
> systems with
> certain memory layouts, with messages like:
>
> imx_sdma: section 16 reloc 0 sym '': relocation 42 out of range
> (0x7f015260 -> 0xc0f5a5e8)
>
> (0x7f015260 is in the module load area, 0xc0f5a5e8 a regular vmalloc
> address; relocation 42 is R_ARM_PREL31)
>
> This is caused by relocatiosn in the .ARM.extab.exit.text and
> .ARM.exidx.exit.text sections referencing the .exit.text section. As
> the
> module loader will omit loading .exit.text without
> CONFIG_MODULE_UNLOAD,
> there will be relocations from loaded to unloaded sections; the
> resulting
> huge offsets trigger the sanity checks added in 050d18d1c651.
>
> IA64 might be affected by a similar issue - sections with names like
> .IA_64.unwind.exit.text and .IA_64.unwind_info.exit.text appear in
> the ld
> script - but I don't know much about that arch.
>
> Also, I'm not sure if this is stable-worthy - just enabling
> CONFIG_MODULE_UNLOAD should be a viable workaround on affected
> kernels.
>
> v2: Use __weak function as suggested by Jessica

Hi Russell,

this patch series is still waiting for your thoughts - in reponse to
v1, Jessica already offered to take it through her tree if you give
your Acked-by.

Thanks,

Matthias


>
>
> Matthias Schiffer (2):
> module: allow arch overrides for .exit section names
> ARM: module: recognize unwind exit sections
>
> arch/arm/kernel/module.c | 7 +++++++
> include/linux/moduleloader.h | 5 +++++
> kernel/module.c | 7 ++++++-
> 3 files changed, 18 insertions(+), 1 deletion(-)
>

2019-06-24 14:10:31

by Jessica Yu

Subject: Re: [PATCH modules v2 0/2] Fix handling of exit unwinding sections (on ARM)

+++ Matthias Schiffer [21/06/19 14:35 +0200]:
>On Fri, 2019-06-07 at 12:49 +0200, Matthias Schiffer wrote:
>> For some time (050d18d1c651 "ARM: 8650/1: module: handle negative
>> R_ARM_PREL31 addends correctly", v4.11+), building a kernel without
>> CONFIG_MODULE_UNLOAD would lead to module loads failing on ARM
>> systems with
>> certain memory layouts, with messages like:
>>
>> imx_sdma: section 16 reloc 0 sym '': relocation 42 out of range
>> (0x7f015260 -> 0xc0f5a5e8)
>>
>> (0x7f015260 is in the module load area, 0xc0f5a5e8 a regular vmalloc
>> address; relocation 42 is R_ARM_PREL31)
>>
>> This is caused by relocatiosn in the .ARM.extab.exit.text and
>> .ARM.exidx.exit.text sections referencing the .exit.text section. As
>> the
>> module loader will omit loading .exit.text without
>> CONFIG_MODULE_UNLOAD,
>> there will be relocations from loaded to unloaded sections; the
>> resulting
>> huge offsets trigger the sanity checks added in 050d18d1c651.
>>
>> IA64 might be affected by a similar issue - sections with names like
>> .IA_64.unwind.exit.text and .IA_64.unwind_info.exit.text appear in
>> the ld
>> script - but I don't know much about that arch.
>>
>> Also, I'm not sure if this is stable-worthy - just enabling
>> CONFIG_MODULE_UNLOAD should be a viable workaround on affected
>> kernels.
>>
>> v2: Use __weak function as suggested by Jessica
>
>Hi Russell,
>
>this patch series is still waiting for your thoughts - in reponse to
>v1, Jessica already offered to take it through her tree if you give
>your Acked-by.
>
>Thanks,
>
>Matthias

Hi Matthias,

There doesn't seem to be any complaints and I think the patchset looks
good, so I've taken it up the modules-next tree. Thanks!

Jessica