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

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Date:   Fri, 21 Jun 2019 14:35:29 +0200
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Russell King <linux@...linux.org.uk>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, Jessica Yu <jeyu@...nel.org>
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(-)
>