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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

  reply	other threads:[~2021-09-10 12:30 UTC|newest]

Thread overview: 29+ 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 13/22] x86: conditionally place regular ASM functions into separate 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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