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From: Arvind Sankar <nivedita@alum.mit.edu>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	James Morse <james.morse@arm.com>, Borislav Petkov <bp@suse.de>,
	Ingo Molnar <mingo@redhat.com>,
	Russell King <linux@armlinux.org.uk>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	x86@kernel.org, clang-built-linux@googlegroups.com,
	linux-arch@vger.kernel.org, linux-efi@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts
Date: Fri, 31 Jul 2020 22:53:25 -0400
Message-ID: <20200801025325.GA2800311@rani.riverdale.lan> (raw)
In-Reply-To: <20200801014755.GA2700342@rani.riverdale.lan>

On Fri, Jul 31, 2020 at 09:47:55PM -0400, Arvind Sankar wrote:
> On Fri, Jul 31, 2020 at 04:08:16PM -0700, Kees Cook wrote:
> > For readability, move the zero-sized sections to the end after DISCARDS
> > and mark them NOLOAD for good measure.
> > 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  arch/x86/boot/compressed/vmlinux.lds.S | 42 +++++++++++++++-----------
> >  1 file changed, 25 insertions(+), 17 deletions(-)
> > 
> > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
> > index 3c2ee9a5bf43..42dea70a5091 100644
> > --- a/arch/x86/boot/compressed/vmlinux.lds.S
> > +++ b/arch/x86/boot/compressed/vmlinux.lds.S
> > @@ -42,18 +42,16 @@ SECTIONS
> >  		*(.rodata.*)
> >  		_erodata = . ;
> >  	}
> > -	.rel.dyn : {
> > -		*(.rel.*)
> > -	}
> > -	.rela.dyn : {
> > -		*(.rela.*)
> > -	}
> > -	.got : {
> > -		*(.got)
> > -	}
> >  	.got.plt : {
> >  		*(.got.plt)
> >  	}
> > +	ASSERT(SIZEOF(.got.plt) == 0 ||
> > +#ifdef CONFIG_X86_64
> > +	       SIZEOF(.got.plt) == 0x18,
> > +#else
> > +	       SIZEOF(.got.plt) == 0xc,
> > +#endif
> > +	       "Unexpected GOT/PLT entries detected!")
> >  
> >  	.data :	{
> >  		_data = . ;
> > @@ -85,13 +83,23 @@ SECTIONS
> >  	ELF_DETAILS
> >  
> >  	DISCARDS
> > -}
> >  
> > -ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
> > -#ifdef CONFIG_X86_64
> > -ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!")
> > -#else
> > -ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
> > -#endif
> > +	/*
> > +	 * Sections that should stay zero sized, which is safer to
> > +	 * explicitly check instead of blindly discarding.
> > +	 */
> > +	.got (NOLOAD) : {
> > +		*(.got)
> > +	}
> > +	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
> >  
> > -ASSERT(SIZEOF(.rel.dyn) == 0 && SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations detected!")
> > +	/* ld.lld does not like .rel* sections being made "NOLOAD". */
> > +	.rel.dyn : {
> > +		*(.rel.*)
> > +	}
> > +	ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
> > +	.rela.dyn : {
> > +		*(.rela.*)
> > +	}
> > +	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
> > +}
> > -- 
> > 2.25.1
> > 
> 
> There's no point in marking zero-size sections NOLOAD -- if the ASSERT's
> passed, they won't be present in the file at all anyway.
> 
> The only section for which there might be a point is .got.plt, which is
> non-empty on 32-bit, and only if it is first moved to the end. That
> saves a few bytes.

Btw, you should move .got.plt also to the end anyway for readability,
it's unused even if non-empty. And with the ASSERT being placed
immediately after it, it's even more distracting from the actual section
layout.

  reply index

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31 23:07 [PATCH v5 00/36] Warn on orphan section placement Kees Cook
2020-07-31 23:07 ` [PATCH v5 01/36] x86/boot/compressed: Move .got.plt entries out of the .got section Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Ard Biesheuvel
2020-07-31 23:07 ` [PATCH v5 02/36] x86/boot/compressed: Force hidden visibility for all symbol references Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Ard Biesheuvel
2020-07-31 23:07 ` [PATCH v5 03/36] x86/boot/compressed: Get rid of GOT fixup code Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Ard Biesheuvel
2020-07-31 23:07 ` [PATCH v5 04/36] x86/boot: Add .text.* to setup.ld Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 05/36] x86/boot: Remove run-time relocations from .head.text code Kees Cook
2020-07-31 23:42   ` Nick Desaulniers
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 06/36] x86/boot: Remove run-time relocations from head_{32,64}.S Kees Cook
2020-08-07 18:12   ` Nick Desaulniers
2020-08-07 20:20     ` Arvind Sankar
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 07/36] x86/boot: Check that there are no run-time relocations Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 08/36] vmlinux.lds.h: Create COMMON_DISCARDS Kees Cook
2020-07-31 23:07 ` [PATCH v5 09/36] vmlinux.lds.h: Add .gnu.version* to COMMON_DISCARDS Kees Cook
2020-07-31 23:07 ` [PATCH v5 10/36] vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections Kees Cook
2020-07-31 23:07 ` [PATCH v5 11/36] vmlinux.lds.h: Split ELF_DETAILS from STABS_DEBUG Kees Cook
2020-07-31 23:07 ` [PATCH v5 12/36] vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to ELF_DETAILS Kees Cook
2020-07-31 23:07 ` [PATCH v5 13/36] vmlinux.lds.h: add PGO and AutoFDO input sections Kees Cook
2020-08-01  3:51   ` Arvind Sankar
2020-08-01  6:18     ` Kees Cook
2020-08-01 17:27       ` Arvind Sankar
2020-08-03 19:05     ` Andi Kleen
2020-08-03 20:15       ` Arvind Sankar
2020-08-04  1:19         ` Fāng-ruì Sòng
2020-08-04  4:45         ` Andi Kleen
2020-08-04  5:32           ` Fāng-ruì Sòng
2020-08-04 16:06           ` Arvind Sankar
2020-08-21 19:18             ` Kees Cook
2020-07-31 23:07 ` [PATCH v5 14/36] efi/libstub: Disable -mbranch-protection Kees Cook
2020-07-31 23:07 ` [PATCH v5 15/36] arm64/mm: Remove needless section quotes Kees Cook
2020-07-31 23:08 ` [PATCH v5 16/36] arm64/kernel: Remove needless Call Frame Information annotations Kees Cook
2020-07-31 23:08 ` [PATCH v5 17/36] arm64/build: Remove .eh_frame* sections due to unwind tables Kees Cook
2020-07-31 23:08 ` [PATCH v5 18/36] arm64/build: Use common DISCARDS in linker script Kees Cook
2020-07-31 23:08 ` [PATCH v5 19/36] arm64/build: Add missing DWARF sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 20/36] arm64/build: Assert for unwanted sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 21/36] arm64/build: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 22/36] arm/build: Refactor linker script headers Kees Cook
2020-07-31 23:08 ` [PATCH v5 23/36] arm/build: Explicitly keep .ARM.attributes sections Kees Cook
2020-08-03 19:02   ` Nick Desaulniers
2020-08-17 22:06     ` Fangrui Song
2020-07-31 23:08 ` [PATCH v5 24/36] arm/build: Add missing sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 25/36] arm/build: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 26/36] arm/boot: Handle all sections explicitly Kees Cook
2020-07-31 23:08 ` [PATCH v5 27/36] arm/boot: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 28/36] x86/asm: Avoid generating unused kprobe sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 29/36] x86/build: Enforce an empty .got.plt section Kees Cook
2020-08-01  2:12   ` Arvind Sankar
2020-08-01  5:32     ` Kees Cook
2020-08-21 17:49     ` Kees Cook
2020-07-31 23:08 ` [PATCH v5 30/36] x86/build: Assert for unwanted sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 31/36] x86/build: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts Kees Cook
2020-08-01  1:47   ` Arvind Sankar
2020-08-01  2:53     ` Arvind Sankar [this message]
2020-08-01  5:36       ` Kees Cook
2020-08-01 17:12         ` Arvind Sankar
2020-08-21 18:24           ` Kees Cook
2020-08-01  5:35     ` Kees Cook
2020-08-01 17:00       ` Arvind Sankar
2020-08-21 18:19     ` Kees Cook
2020-07-31 23:08 ` [PATCH v5 33/36] x86/boot/compressed: Remove, discard, or assert for unwanted sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 34/36] x86/boot/compressed: Add missing debugging sections to output Kees Cook
2020-07-31 23:08 ` [PATCH v5 35/36] x86/boot/compressed: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 36/36] arm/build: Assert for unwanted sections Kees Cook

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