From: Jessica Yu <jeyu@kernel.org>
To: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
keescook@chromium.org, Josh Poimboeuf <jpoimboe@redhat.com>,
Miroslav Benes <mbenes@suse.cz>
Subject: Re: [PATCH v2] module: Harden STRICT_MODULE_RWX
Date: Mon, 10 Aug 2020 17:06:50 +0200 [thread overview]
Message-ID: <20200810150647.GB8612@linux-8ccs> (raw)
In-Reply-To: <20200810092523.GA8612@linux-8ccs>
+++ Jessica Yu [10/08/20 11:25 +0200]:
>+++ Mauro Carvalho Chehab [08/08/20 10:12 +0200]:
>[snip]
>>Right now, what happens is:
>>
>> # modprobe wlcore
>> modprobe: ERROR: could not insert 'wlcore': Exec format error
>>
>>This seems to be failing for all modules, as doesn't show anything
>>probed.
>>
>>Btw, IMO, it would be useful to have some pr_debug() infra in order to
>>explain why insmod is failing, or to have more error codes used there,
>>as nothing was printed at dmesg. That makes harder to debug issues
>>there. I ended losing a lot of time yesterday rebuilding the Kernel
>>and checking the FS, before deciding to add some printks inside the
>>Kernel ;-)
>>
>>In order for modprobe to start working again, I had to apply this
>>dirty hack:
>>
>><hack>
>>diff --git a/kernel/module.c b/kernel/module.c
>>index 910a57640818..10d590dc48ad 100644
>>--- a/kernel/module.c
>>+++ b/kernel/module.c
>>@@ -2051,11 +2051,12 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
>> const unsigned long shf_wx = SHF_WRITE|SHF_EXECINSTR;
>> int i;
>>
>>+#if 0
>> for (i = 0; i < hdr->e_shnum; i++) {
>> if ((sechdrs[i].sh_flags & shf_wx) == shf_wx)
>> return -ENOEXEC;
>> }
>>-
>>+#endif
>> return 0;
>>}
>></hack>
[ I somehow munged the To: header in the last mail. Sorry about that,
it's fixed now. ]
>All this hunk does it reject loading modules that have any sections
>that have both the writable and executable flags. You're saying it's
>happening for all modules on your setup - I am curious as to which
>sections have both these flags - what does readelf -S tell you?
Hmm, I was not able to reproduce this with a cross-compiled kernel
using the attached config (gcc 9.3.0 with vanilla v5.8 kernel). I am
curious if the failing sections are also SHF_ALLOC - in that case, the
code is doing what it is intended to do, which is rejecting loading
any modules with writable and executable sections. If the problematic
sections are *not* SHF_ALLOC, then we might be able to work around
that by ignoring non-SHF_ALLOC sections as they are not copied to the
final module location anyway.
Jessica
next prev parent reply other threads:[~2020-08-10 15:07 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-03 17:13 [PATCH v2] module: Harden STRICT_MODULE_RWX Peter Zijlstra
2020-04-03 20:31 ` Kees Cook
2020-04-08 15:32 ` Jessica Yu
2020-04-08 15:43 ` [PATCH] module: break nested ARCH_HAS_STRICT_MODULE_RWX and STRICT_MODULE_RWX #ifdefs Jessica Yu
2020-04-08 15:57 ` [PATCH v2] module: Harden STRICT_MODULE_RWX Peter Zijlstra
2020-04-08 16:20 ` Jessica Yu
2020-08-08 8:12 ` Mauro Carvalho Chehab
2020-08-10 9:25 ` Jessica Yu
2020-08-10 15:06 ` Jessica Yu [this message]
2020-08-11 14:34 ` Mauro Carvalho Chehab
2020-08-11 14:55 ` peterz
2020-08-11 15:27 ` Mauro Carvalho Chehab
2020-08-11 16:01 ` Jessica Yu
2020-08-11 16:57 ` Will Deacon
2020-08-11 17:59 ` peterz
2020-08-11 21:29 ` Peter Zijlstra
2020-08-12 8:56 ` Ard Biesheuvel
2020-08-12 10:40 ` peterz
2020-08-12 11:41 ` Jessica Yu
2020-08-12 13:14 ` H.J. Lu
2020-08-12 12:56 ` Will Deacon
2020-08-12 14:15 ` Szabolcs Nagy
2020-08-12 16:00 ` Jessica Yu
2020-08-12 16:37 ` Ard Biesheuvel
2020-08-12 16:42 ` Szabolcs Nagy
2020-08-13 9:00 ` Will Deacon
2020-08-12 20:00 ` Peter Zijlstra
2020-08-13 8:36 ` Ard Biesheuvel
2020-08-13 13:04 ` Jessica Yu
2020-08-13 13:07 ` Ard Biesheuvel
2020-08-21 12:20 ` Will Deacon
2020-08-21 12:27 ` Ard Biesheuvel
2020-08-21 12:30 ` Will Deacon
2020-08-22 13:47 ` Ard Biesheuvel
2020-08-24 15:24 ` Jessica Yu
2020-08-25 1:54 ` Masahiro Yamada
2020-08-31 9:46 ` Jessica Yu
2020-08-31 10:42 ` Masahiro Yamada
2020-08-31 13:25 ` Ard Biesheuvel
2020-08-31 15:31 ` Jessica Yu
2020-08-31 15:46 ` Masahiro Yamada
2020-09-03 12:37 ` Jessica Yu
2020-09-01 12:51 ` Will Deacon
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