linux-kernel - Re: [PATCH v2] module: Harden STRICT_MODULE

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Date:   Thu, 3 Sep 2020 14:37:40 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Mark Rutland <mark.rutland@....com>, nd <nd@....com>
Subject: Re: [PATCH v2] module: Harden STRICT_MODULE_RWX

+++ Masahiro Yamada [31/08/20 19:42 +0900]:
[snipped for brevity]
>Sorry for the delay.
>
>Please try the attached patch.

Hi Masahiro,

Thank you for the patch. Sorry for the delay, I just wanted to report back
after briefly testing your patch. It works great, at the moment I've only
tested with arm64.

I made the following change to arch/arm64/include/asm/module.lds.h:

diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index 691f15af788e..d8e786e5fcdb 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -2,6 +2,8 @@
 SECTIONS {
        .plt (NOLOAD) : { BYTE(0) }
        .init.plt (NOLOAD) : { BYTE(0) }
+#ifdef CONFIG_DYNAMIC_FTRACE
        .text.ftrace_trampoline (NOLOAD) : { BYTE(0) }
+#endif
 }
 #endif

Since originally we wanted to include .text.ftrace_trampoline only conditionally.

The resulting scripts/module.lds looks correct with CONFIG_DYNAMIC_FTRACE=y:

SECTIONS {
 /DISCARD/ : {
  *(.discard)
  *(.discard.*)
 }
 __ksymtab 0 : { *(SORT(___ksymtab+*)) }
 __ksymtab_gpl 0 : { *(SORT(___ksymtab_gpl+*)) }
 __ksymtab_unused 0 : { *(SORT(___ksymtab_unused+*)) }
 __ksymtab_unused_gpl 0 : { *(SORT(___ksymtab_unused_gpl+*)) }
 __ksymtab_gpl_future 0 : { *(SORT(___ksymtab_gpl_future+*)) }
 __kcrctab 0 : { *(SORT(___kcrctab+*)) }
 __kcrctab_gpl 0 : { *(SORT(___kcrctab_gpl+*)) }
 __kcrctab_unused 0 : { *(SORT(___kcrctab_unused+*)) }
 __kcrctab_unused_gpl 0 : { *(SORT(___kcrctab_unused_gpl+*)) }
 __kcrctab_gpl_future 0 : { *(SORT(___kcrctab_gpl_future+*)) }
 .init_array 0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
 __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
}
SECTIONS {
 .plt (NOLOAD) : { BYTE(0) }
 .init.plt (NOLOAD) : { BYTE(0) }
 .text.ftrace_trampoline (NOLOAD) : { BYTE(0) }
} 

And with CONFIG_DYNAMIC_FTRACE=n as well:

SECTIONS {
 .plt (NOLOAD) : { BYTE(0) }
 .init.plt (NOLOAD) : { BYTE(0) }
}

I will test on more arches in the next days but in the meantime you could add my

    Tested-by: Jessica Yu <jeyu@...nel.org>

Thank you for working on this!