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From: Michael Ellerman <mpe@ellerman.id.au>
To: Kees Cook <keescook@chromium.org>, Borislav Petkov <bp@alien8.de>
Cc: Kees Cook <keescook@chromium.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Will Deacon <will@kernel.org>,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org,
	linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org,
	linux-c6x-dev@linux-c6x.org,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Michal Simek <monstr@monstr.eu>,
	linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Joel Stanley <joel@jms.id.au>,
	Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [PATCH v2 02/29] powerpc: Remove PT_NOTE workaround
Date: Fri, 11 Oct 2019 17:07:04 +1100
Message-ID: <878sprx1br.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20191011000609.29728-3-keescook@chromium.org>

Kees Cook <keescook@chromium.org> writes:
> In preparation for moving NOTES into RO_DATA, remove the PT_NOTE
> workaround since the kernel requires at least gcc 4.6 now.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  arch/powerpc/kernel/vmlinux.lds.S | 24 ++----------------------
>  1 file changed, 2 insertions(+), 22 deletions(-)

Acked-by: Michael Ellerman <mpe@ellerman.id.au>

For the archives, Joel tried a similar patch a while back which caused
some problems, see:

  https://lore.kernel.org/linuxppc-dev/20190321003253.22100-1-joel@jms.id.au/

and a v2:

  https://lore.kernel.org/linuxppc-dev/20190329064453.12761-1-joel@jms.id.au/

This is similar to his v2. The only outstanding comment on his v2 was
from Segher:
  (And I do not know if there are any tools that expect the notes in a phdr,
  or even specifically the second phdr).

But this patch solves that by not changing the note.

cheers

> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index 81e672654789..a3c8492b2b19 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -20,20 +20,6 @@ ENTRY(_stext)
>  PHDRS {
>  	kernel PT_LOAD FLAGS(7); /* RWX */
>  	note PT_NOTE FLAGS(0);
> -	dummy PT_NOTE FLAGS(0);
> -
> -	/* binutils < 2.18 has a bug that makes it misbehave when taking an
> -	   ELF file with all segments at load address 0 as input.  This
> -	   happens when running "strip" on vmlinux, because of the AT() magic
> -	   in this linker script.  People using GCC >= 4.2 won't run into
> -	   this problem, because the "build-id" support will put some data
> -	   into the "notes" segment (at a non-zero load address).
> -
> -	   To work around this, we force some data into both the "dummy"
> -	   segment and the kernel segment, so the dummy segment will get a
> -	   non-zero load address.  It's not enough to always create the
> -	   "notes" segment, since if nothing gets assigned to it, its load
> -	   address will be zero.  */
>  }
>  
>  #ifdef CONFIG_PPC64
> @@ -178,14 +164,8 @@ SECTIONS
>  	EXCEPTION_TABLE(0)
>  
>  	NOTES :kernel :note
> -
> -	/* The dummy segment contents for the bug workaround mentioned above
> -	   near PHDRS.  */
> -	.dummy : AT(ADDR(.dummy) - LOAD_OFFSET) {
> -		LONG(0)
> -		LONG(0)
> -		LONG(0)
> -	} :kernel :dummy
> +	/* Restore program header away from PT_NOTE. */
> +	.dummy : { *(.dummy) } :kernel
>  
>  /*
>   * Init sections discarded at runtime
> -- 
> 2.17.1

  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11  0:05 [PATCH v2 00/29] vmlinux.lds.h: Refactor EXCEPTION_TABLE and NOTES Kees Cook
2019-10-11  0:05 ` [PATCH v2 01/29] powerpc: Rename "notes" PT_NOTE to "note" Kees Cook
2019-10-11  6:00   ` Michael Ellerman
2019-10-11  8:25   ` Segher Boessenkool
2019-10-11 16:11     ` Kees Cook
2019-10-11 16:25       ` Segher Boessenkool
2019-10-15 16:54         ` Borislav Petkov
2019-10-15 17:36           ` Kees Cook
2019-10-11  0:05 ` [PATCH v2 02/29] powerpc: Remove PT_NOTE workaround Kees Cook
2019-10-11  6:07   ` Michael Ellerman [this message]
2019-10-11 16:09     ` Kees Cook
2019-10-11  0:05 ` [PATCH v2 03/29] powerpc: Rename PT_LOAD identifier "kernel" to "text" Kees Cook
2019-10-11  6:07   ` Michael Ellerman
2019-10-11  0:05 ` [PATCH v2 04/29] alpha: " Kees Cook
2019-10-11  0:05 ` [PATCH v2 05/29] ia64: Rename PT_LOAD identifier "code" " Kees Cook
2019-10-11  0:05 ` [PATCH v2 06/29] s390: Move RO_DATA into "text" PT_LOAD Program Header Kees Cook
2019-10-11  0:05 ` [PATCH v2 07/29] x86: Restore "text" Program Header with dummy section Kees Cook
2019-10-11  0:05 ` [PATCH v2 08/29] vmlinux.lds.h: Provide EMIT_PT_NOTE to indicate export of .notes Kees Cook
2019-10-11  0:05 ` [PATCH v2 09/29] vmlinux.lds.h: Move Program Header restoration into NOTES macro Kees Cook
2019-10-11  0:05 ` [PATCH v2 10/29] vmlinux.lds.h: Move NOTES into RO_DATA Kees Cook
2019-10-11  0:05 ` [PATCH v2 11/29] vmlinux.lds.h: Replace RODATA with RO_DATA Kees Cook
2019-10-11  0:05 ` [PATCH v2 12/29] vmlinux.lds.h: Replace RO_DATA_SECTION " Kees Cook
2019-10-11  7:49   ` Geert Uytterhoeven
2019-10-11  0:05 ` [PATCH v2 13/29] vmlinux.lds.h: Replace RW_DATA_SECTION with RW_DATA Kees Cook
2019-10-11  7:49   ` Geert Uytterhoeven
2019-10-11  0:05 ` [PATCH v2 14/29] vmlinux.lds.h: Allow EXCEPTION_TABLE to live in RO_DATA Kees Cook
2019-10-11  0:05 ` [PATCH v2 15/29] x86: Actually use _etext for end of text segment Kees Cook
2019-10-11  0:05 ` [PATCH v2 16/29] x86: Move EXCEPTION_TABLE to RO_DATA segment Kees Cook
2019-10-11  0:05 ` [PATCH v2 17/29] alpha: " Kees Cook
2019-10-11  0:05 ` [PATCH v2 18/29] arm64: " Kees Cook
2019-10-11  0:05 ` [PATCH v2 19/29] c6x: " Kees Cook
2019-10-11  0:06 ` [PATCH v2 20/29] h8300: " Kees Cook
2019-10-11  0:06 ` [PATCH v2 21/29] ia64: " Kees Cook
2019-10-11  0:06 ` [PATCH v2 22/29] microblaze: " Kees Cook
2019-10-11  0:06 ` [PATCH v2 23/29] parisc: " Kees Cook
2019-10-12  9:50   ` Helge Deller
2019-10-11  0:06 ` [PATCH v2 24/29] powerpc: " Kees Cook
2019-10-11  0:06 ` [PATCH v2 25/29] xtensa: " Kees Cook
2019-10-14  7:41   ` Max Filippov
2019-10-11  0:06 ` [PATCH v2 26/29] x86/mm: Remove redundant &s on addresses Kees Cook
2019-10-11  0:06 ` [PATCH v2 27/29] x86/mm: Report which part of kernel image is freed Kees Cook
2019-10-11  0:06 ` [PATCH v2 28/29] x86/mm: Report actual image regions in /proc/iomem Kees Cook
2019-10-11  0:06 ` [PATCH v2 29/29] x86: Use INT3 instead of NOP for linker fill bytes Kees Cook

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