On Thu, Sep 03, 2020 at 07:42:15PM -0400, Arvind Sankar wrote:

On Thu, Sep 03, 2020 at 02:44:41PM -0700, Kees Cook wrote:

quoted

On Thu, Sep 03, 2020 at 01:30:26PM -0700, Sami Tolvanen wrote:

quoted

From: Arvind Sankar <redacted>

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/ (local)
[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/ (local)

Reported-by: Nick Desaulniers <redacted>
Signed-off-by: Arvind Sankar <redacted>

Reviewed-by: Kees Cook <redacted>

-- 
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.

It is still necessary for tip of tree LLVM to work properly
(specifically clang and ld.lld) regardless of whether or not LTO is
used.

[4] also fixes it but I don't think it can be backported to stable so it
would still be nice to get it picked up so that it can be sent back
there. We have been carrying it in our CI for a decent amount of time...

Cheers,
Nathan

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