linux-kernel - Re: [PATCH v2 01/28] x86/boot/compressed: Disable relocation relaxation

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Date:   Thu, 3 Sep 2020 19:42:15 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Kees Cook <keescook@...omium.org>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org, Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH v2 01/28] x86/boot/compressed: Disable relocation
 relaxation

On Thu, Sep 03, 2020 at 02:44:41PM -0700, Kees Cook wrote:
> On Thu, Sep 03, 2020 at 01:30:26PM -0700, Sami Tolvanen wrote:
> > From: Arvind Sankar <nivedita@...m.mit.edu>
> > 
> > Patch series [4] is a solution to allow the compressed kernel to be
> > linked with -pie unconditionally, but even if merged is unlikely to be
> > backported. As a simple solution that can be applied to stable as well,
> > prevent the assembler from generating the relaxed relocation types using
> > the -mrelax-relocations=no option. For ease of backporting, do this
> > unconditionally.
> > 
> > [0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65
> > [1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/
> > [2] https://github.com/ClangBuiltLinux/linux/issues/1121
> > [3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0
> > [4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/
> > 
> > Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>
> 
> -- 
> Kees Cook

Note that since [4] is now in tip, assuming it doesn't get dropped for
some reason, this patch isn't necessary unless you need to backport this
LTO series to 5.9 or below.

Thanks.