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

From: Jessica Yu
Date: Mon Jun 24 2019 - 08:32:07 EST


+++ 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