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

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Message-Id: <20190607104912.6252-1-matthias.schiffer@ew.tq-group.com>
Date:   Fri,  7 Jun 2019 12:49:10 +0200
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Russell King <linux@...linux.org.uk>, Jessica Yu <jeyu@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org,
        Matthias Schiffer <matthias.schiffer@...tq-group.com>
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