linux-kernel - [PATCH] ARM: module: treat exit sections the same as init sections when !CONFIG_MODULE

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Date:   Fri,  7 May 2021 14:13:22 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jessica Yu <jeyu@...nel.org>
Subject: [PATCH] ARM: module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD

Dynamic code patching (alternatives, jump_label and static_call) can
have sites in __exit code, even if __exit is never executed. Therefore
__exit must be present at runtime, at least for as long as __init code is.

Additionally, for jump_label and static_call, the __exit sites must also
identify as within_module_init(), such that the infrastructure is aware
to never touch them after module init -- alternatives are only ran once
at init and hence don't have this particular constraint.

Previously, the module loader never loaded the exit sections in the first
place when CONFIG_MODULE_UNLOAD=n. Commit 33121347fb1c ("module: treat exit
sections the same as init sections when !CONFIG_MODULE_UNLOAD") addressed
the issue by having the module loader load the exit sections and then making
__exit identify as __init for !MODULE_UNLOAD. Then, since they are treated
like init sections, they will be also discarded after init.

That commit satisfied the above requirements for jump_labels and
static_calls by modifying the checks in the core module_init_section()
function in kernel/module.c to include exit sections. However, ARM
overrides these and implements their own module_{init,exit}_section()
functions. Add a similar check for exit sections to ARM's
module_init_section() function so that all arches are on the same page.

Fixes: 33121347fb1c ("module: treat exit sections the same as init
sections when !CONFIG_MODULE_UNLOAD")
Link: https://lore.kernel.org/lkml/YFiuphGw0RKehWsQ@gunter/
Link: https://lore.kernel.org/r/20210323142756.11443-1-jeyu@kernel.org
Signed-off-by: Jessica Yu <jeyu@...nel.org>
---
 arch/arm/kernel/module.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index beac45e89ba6..9d403fc1893b 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c
@@ -56,9 +56,16 @@ void *module_alloc(unsigned long size)

 bool module_init_section(const char *name)
 {
+#ifndef CONFIG_MODULE_UNLOAD
+	return strstarts(name, ".init") ||
+		strstarts(name, ".ARM.extab.init") ||
+		strstarts(name, ".ARM.exidx.init") ||
+		module_exit_section(name);
+#else
 	return strstarts(name, ".init") ||
 		strstarts(name, ".ARM.extab.init") ||
 		strstarts(name, ".ARM.exidx.init");
+#endif
 }

 bool module_exit_section(const char *name)
-- 
2.31.1