From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>,
linux-hardening@vger.kernel.org,
Kristen C Accardi <kristen.c.accardi@intel.com>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
Kees Cook <keescook@chromium.org>,
Masahiro Yamada <masahiroy@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>, Jessica Yu <jeyu@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Marios Pomonis <pomonis@google.com>,
Sami Tolvanen <samitolvanen@google.com>,
Tony Luck <tony.luck@intel.com>, Ard Biesheuvel <ardb@kernel.org>,
Jesse Brandeburg <jesse.brandeburg@intel.com>,
Lukasz Czapnik <lukasz.czapnik@intel.com>,
Marta A Plantykow <marta.a.plantykow@intel.com>,
Michal Kubiak <michal.kubiak@intel.com>,
Michal Swiatkowski <michal.swiatkowski@intel.com>,
linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
live-patching@vger.kernel.org
Subject: Re: [PATCH v6 kspp-next 16/22] livepatch: only match unique symbols when using fgkaslr
Date: Fri, 10 Sep 2021 14:29:53 +0200 [thread overview]
Message-ID: <20210910122953.400-1-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <alpine.LSU.2.21.2109091347400.20761@pobox.suse.cz>
From: Miroslav Benes <mbenes@suse.cz>
Date: Thu, 9 Sep 2021 13:53:35 +0200 (CEST)
> Hi,
Hi!
> On Tue, 31 Aug 2021, Alexander Lobakin wrote:
>
> > From: Kristen Carlson Accardi <kristen@linux.intel.com>
> >
> > If any type of function granular randomization is enabled, the sympos
> > algorithm will fail, as it will be impossible to resolve symbols when
> > there are duplicates using the previous symbol position.
> >
> > Override the value of sympos to always be zero if fgkaslr is enabled for
> > either the core kernel or modules, forcing the algorithm
> > to require that only unique symbols are allowed to be patched.
> >
> > Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
> > ---
> > kernel/livepatch/core.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index 335d988bd811..852bbfa9da7b 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -169,6 +169,17 @@ static int klp_find_object_symbol(const char *objname, const char *name,
> > else
> > kallsyms_on_each_symbol(klp_find_callback, &args);
> >
> > + /*
> > + * If any type of function granular randomization is enabled, it
> > + * will be impossible to resolve symbols when there are duplicates
> > + * using the previous symbol position (i.e. sympos != 0). Override
> > + * the value of sympos to always be zero in this case. This will
> > + * force the algorithm to require that only unique symbols are
> > + * allowed to be patched.
> > + */
> > + if (IS_ENABLED(CONFIG_FG_KASLR))
> > + sympos = 0;
> > +
>
> I ran the live patching tests and no problem occurred, which is great. We
> do not have a test for old_sympos, which makes the testing less telling,
> but at least nothing blows up with the section randomization itself.
Great, thanks!
> However, I want to reiterate what I wrote for the same patch in v5
> series.
>
> The above hunk should work, but I wonder if we should make it more
> explicit. With the change the user will get the error with "unresolvable
> ambiguity for symbol..." if they specify sympos and the symbol is not
> unique. It could confuse them.
>
> So, how about it making it something like
>
> if (IS_ENABLED(CONFIG_FG_KASLR) || IS_ENABLED(CONFIG_MODULE_FG_KASLR))
> if (sympos) {
> pr_err("fgkaslr is enabled, specifying sympos for symbol '%s' in object '%s' does not work.\n",
> name, objname);
> *addr = 0;
> return -EINVAL;
> }
>
> ? (there could be goto to the error out at the end of the function to
> save copy-pasting).
>
> In that case, if sympos is not specified, the user will get the message
> which matches the reality. If the user specifies it, they will get the
> error in case of fgkaslr (no matter if the symbol is found or not).
Not familiar with livepatching unfortunately, hope Kristen and/or
Kees will comment on this. Looks fine for me anyways.
> What do you think?
>
> Miroslav
Thanks,
Al
next prev parent reply other threads:[~2021-09-10 12:30 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-31 14:40 [PATCH v6 kspp-next 00/22] Function Granular KASLR Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 01/22] kbuild: Fix TRIM_UNUSED_KSYMS with LTO_CLANG Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 02/22] kbuild: merge vmlinux_link() between the ordinary link and Clang LTO Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 03/22] kbuild: do not remove 'linux' link in scripts/link-vmlinux.sh Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 04/22] kbuild: merge vmlinux_link() between ARCH=um and other architectures Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 05/22] x86: tools/relocs: Support >64K section headers Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 06/22] x86/boot: Allow a "silent" kaslr random byte fetch Alexander Lobakin
2021-08-31 14:40 ` [PATCH v6 kspp-next 07/22] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 08/22] Make sure ORC lookup covers the entire _etext - _stext Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 09/22] x86/tools: Add relative relocs for randomized functions Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 10/22] x86/boot/compressed: Avoid duplicate malloc() implementations Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 11/22] x86: Add support for function granular KASLR Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 12/22] linkage: add macros for putting ASM functions into own sections Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 14/22] FG-KASLR: use a scripted approach to handle .text.* sections Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 15/22] kallsyms: Hide layout Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 16/22] livepatch: only match unique symbols when using fgkaslr Alexander Lobakin
2021-09-09 11:53 ` Miroslav Benes
2021-09-10 12:29 ` Alexander Lobakin [this message]
2021-08-31 14:41 ` [PATCH v6 kspp-next 17/22] x86/boot: allow FG-KASLR to be selected Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 18/22] arm64/crypto: conditionally place ASM functions into separate sections Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 19/22] module: Reorder functions Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 20/22] module: use a scripted approach for FG-KASLR Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 21/22] Documentation: add a documentation " Alexander Lobakin
2021-08-31 14:41 ` [PATCH v6 kspp-next 22/22] maintainers: add MAINTAINERS entry " Alexander Lobakin
2021-08-31 17:27 ` [PATCH v6 kspp-next 00/22] Function Granular KASLR Kees Cook
2021-09-01 10:36 ` Alexander Lobakin
2021-09-02 1:36 ` Kees Cook
2021-09-03 11:19 ` Alexander Lobakin
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