From: Ard Biesheuvel <ardb@kernel.org>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>, Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Kees Cook <keescook@chromium.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Miroslav Benes <mbenes@suse.cz>,
Mark Rutland <mark.rutland@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v2] module: Harden STRICT_MODULE_RWX
Date: Mon, 31 Aug 2020 16:25:42 +0300 [thread overview]
Message-ID: <CAMj1kXGRtmj_4GKFbcHnugwn6Vpj9Fnzii7My0wrGL_j1Xh8sw@mail.gmail.com> (raw)
In-Reply-To: <CAK7LNARc1vjAV5ib1D0LaQA+rNGcE7YwGnp-MrshGD34_7V4WQ@mail.gmail.com>
On Mon, 31 Aug 2020 at 13:43, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Mon, Aug 31, 2020 at 6:47 PM Jessica Yu <jeyu@kernel.org> wrote:
> >
> > +++ Will Deacon [21/08/20 13:30 +0100]:
> > [snipped]
> > >> > > > So module_enforce_rwx_sections() is already called after
> > >> > > > module_frob_arch_sections() - which really baffled me at first, since
> > >> > > > sh_type and sh_flags should have been set already in
> > >> > > > module_frob_arch_sections().
> > >> > > >
> > >> > > > I added some debug prints to see which section the module code was
> > >> > > > tripping on, and it was .text.ftrace_trampoline. See this snippet from
> > >> > > > arm64's module_frob_arch_sections():
> > >> > > >
> > >> > > > else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&
> > >> > > > !strcmp(secstrings + sechdrs[i].sh_name,
> > >> > > > ".text.ftrace_trampoline"))
> > >> > > > tramp = sechdrs + i;
> > >> > > >
> > >> > > > Since Mauro's config doesn't have CONFIG_DYNAMIC_FTRACE enabled, tramp
> > >> > > > is never set here and the if (tramp) check at the end of the function
> > >> > > > fails, so its section flags are never set, so they remain WAX and fail
> > >> > > > the rwx check.
> > >> > >
> > >> > > Right. Our module.lds does not go through the preprocessor, so we
> > >> > > cannot add the #ifdef check there currently. So we should either drop
> > >> > > the IS_ENABLED() check here, or simply rename the section, dropping
> > >> > > the .text prefix (which doesn't seem to have any significance outside
> > >> > > this context)
> > >> > >
> > >> > > I'll leave it to Will to make the final call here.
> > >> >
> > >> > Why don't we just preprocess the linker script, like we do for the main
> > >> > kernel?
> > >> >
> > >>
> > >> That should work as well, I just haven't checked how straight-forward
> > >> it is to change that.
> > >
> > >Ok, if it's _not_ straightforward, then let's just drop the IS_ENABLED()
> > >altogether.
> >
> > Unfortunately I've been getting more reports about this issue, so let's just
> > get the aforementioned workaround merged first. Does the following look OK?
> >
> > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
> > index 0ce3a28e3347..2e224435c024 100644
> > --- a/arch/arm64/kernel/module-plts.c
> > +++ b/arch/arm64/kernel/module-plts.c
> > @@ -305,8 +305,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> > mod->arch.core.plt_shndx = i;
> > else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
> > mod->arch.init.plt_shndx = i;
> > - else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&
> > - !strcmp(secstrings + sechdrs[i].sh_name,
> > + else if (!strcmp(secstrings + sechdrs[i].sh_name,
> > ".text.ftrace_trampoline"))
> > tramp = sechdrs + i;
> > else if (sechdrs[i].sh_type == SHT_SYMTAB)
> >
> > If so I'll turn it into a formal patch and we can get that merged in the next -rc.
> >
> > Thanks,
> >
> > Jessica
>
>
>
> Sorry for the delay.
>
> Please try the attached patch.
>
Thanks Masahiro,
I'll leave it to the maintainers to make the final call, but this does
look rather intrusive to me, especially for an -rc. Renaming
scripts/module-common.lds to scripts/module.lds means that the distros
may have to update their scripts to generate the linux-headers
packages etc, so if we do this at all, we'd better do it between
releases.
next prev parent reply other threads:[~2020-08-31 13:26 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
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 [this message]
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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