linux-kernel - Re: [PATCH 5.4 v2 1/6] x86, vmlinux.lds: Add RUNTIME_DISCARD

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Date:   Thu, 23 Feb 2023 13:08:36 -0600
From:   Tom Saeger <tom.saeger@...cle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sasha Levin <sashal@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Rich Felker <dalias@...c.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Dennis Gilmore <dennis@...il.us>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        "H.J. Lu" <hjl.tools@...il.com>, Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 5.4 v2 1/6] x86, vmlinux.lds: Add RUNTIME_DISCARD_EXIT to
 generic DISCARDS

On Thu, Feb 23, 2023 at 10:50:22AM +0100, Greg Kroah-Hartman wrote:
> On Fri, Feb 10, 2023 at 01:20:22PM -0700, Tom Saeger wrote:
> > From: "H.J. Lu" <hjl.tools@...il.com>
> > 
> > commit 84d5f77fc2ee4e010c2c037750e32f06e55224b0 upstream.
> > 
> > In the x86 kernel, .exit.text and .exit.data sections are discarded at
> > runtime, not by the linker. Add RUNTIME_DISCARD_EXIT to generic DISCARDS
> > and define it in the x86 kernel linker script to keep them.
> > 
> > The sections are added before the DISCARD directive so document here
> > only the situation explicitly as this change doesn't have any effect on
> > the generated kernel. Also, other architectures like ARM64 will use it
> > too so generalize the approach with the RUNTIME_DISCARD_EXIT define.
> > 
> >  [ bp: Massage and extend commit message. ]
> > 
> > Signed-off-by: H.J. Lu <hjl.tools@...il.com>
> > Signed-off-by: Borislav Petkov <bp@...e.de>
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > Link: https://lkml.kernel.org/r/20200326193021.255002-1-hjl.tools@gmail.com
> > Signed-off-by: Tom Saeger <tom.saeger@...cle.com>
> > ---
> >  arch/x86/kernel/vmlinux.lds.S     |  1 +
> >  include/asm-generic/vmlinux.lds.h | 11 +++++++++--
> >  2 files changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index 1afe211d7a7c..0ae3cd9a25ea 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -21,6 +21,7 @@
> >  #define LOAD_OFFSET __START_KERNEL_map
> >  #endif
> >  
> > +#define RUNTIME_DISCARD_EXIT
> >  #include <asm-generic/vmlinux.lds.h>
> >  #include <asm/asm-offsets.h>
> >  #include <asm/thread_info.h>
> 
> Does this backport look correct from a style point-of-view?

I debated about this.

> 
> Hint, extra blank line needed after the define, like what is done in the
> original...

I did check, truly.  See attached git-cherry-vimdiff

I show the blank line introduced here (which isn't in 5.4.y):
441110a547f8 ("vmlinux.lds.h: Provide EMIT_PT_NOTE to indicate export of .notes")

And wasn't sure whether to stay with the original or add a blank.
I chose the former.
I chose wrong.
Now I know.

Cheers,

--Tom

> 
> thanks,
> 
> greg k-h

View attachment "git-cherry-vimdiff" of type "text/plain" (645 bytes)