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Mon, 17 Aug 2020 15:06:32 -0700 (PDT) Date: Mon, 17 Aug 2020 15:06:29 -0700 From: Fangrui Song To: Nick Desaulniers Subject: Re: [PATCH v5 23/36] arm/build: Explicitly keep .ARM.attributes sections Message-ID: <20200817220629.3pkabegeedomsaaz@google.com> References: <20200731230820.1742553-1-keescook@chromium.org> <20200731230820.1742553-24-keescook@chromium.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200817_180637_352852_34A4A98E X-CRM114-Status: GOOD ( 18.96 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , linux-arch , linux-efi , Kees Cook , Arnd Bergmann , Peter Collingbourne , Catalin Marinas , Masahiro Yamada , "maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" , Russell King , LKML , Nathan Chancellor , clang-built-linux , Arvind Sankar , Ingo Molnar , James Morse , Thomas Gleixner , Borislav Petkov , Will Deacon , Ard Biesheuvel , Linux ARM Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-08-03, 'Nick Desaulniers' via Clang Built Linux wrote: >On Fri, Jul 31, 2020 at 4:18 PM Kees Cook wrote: >> >> In preparation for adding --orphan-handling=warn, explicitly keep the >> .ARM.attributes section by expanding the existing ELF_DETAILS macro into >> ARM_DETAILS. >> >> Suggested-by: Nick Desaulniers >> Link: https://lore.kernel.org/lkml/CAKwvOdk-racgq5pxsoGS6Vtifbtrk5fmkmnoLxrQMaOvV0nPWw@mail.gmail.com/ >> Signed-off-by: Kees Cook >> --- >> arch/arm/include/asm/vmlinux.lds.h | 4 ++++ >> arch/arm/kernel/vmlinux-xip.lds.S | 2 +- >> arch/arm/kernel/vmlinux.lds.S | 2 +- >> 3 files changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm/include/asm/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h >> index a08f4301b718..c4af5182ab48 100644 >> --- a/arch/arm/include/asm/vmlinux.lds.h >> +++ b/arch/arm/include/asm/vmlinux.lds.h >> @@ -52,6 +52,10 @@ >> ARM_MMU_DISCARD(*(__ex_table)) \ >> COMMON_DISCARDS >> >> +#define ARM_DETAILS \ >> + ELF_DETAILS \ >> + .ARM.attributes 0 : { *(.ARM.attributes) } > >I had to look up what the `0` meant: >https://sourceware.org/binutils/docs/ld/Output-Section-Attributes.html#Output-Section-Attributes >mentions it's an "address" and >https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_chapter/ld_3.html#SEC21 >mentions it as "start" (an address). >Unless we need those, can we drop them? (Sorry for the resulting churn >that would cause). I think the NO_LOAD stuff makes more sense, but >I'm curious if the kernel checks for that. NOLOAD means SHT_NOBITS (usually SHF_ALLOC). .ARM.attributes is a non-SHF_ALLOC section. An explicit 0 (output section address) is good - GNU ld's internal linker scripts (ld --verbose output) use 0 for such non-SHF_ALLOC sections. Without the 0, the section may get a non-zero address, which is not wrong - but probably does not look well. See https://reviews.llvm.org/D85867 for details. Reviewed-by: Fangrui Song >> + >> #define ARM_STUBS_TEXT \ >> *(.gnu.warning) \ >> *(.glue_7) \ >> diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S >> index 904c31fa20ed..57fcbf55f913 100644 >> --- a/arch/arm/kernel/vmlinux-xip.lds.S >> +++ b/arch/arm/kernel/vmlinux-xip.lds.S >> @@ -150,7 +150,7 @@ SECTIONS >> _end = .; >> >> STABS_DEBUG >> - ELF_DETAILS >> + ARM_DETAILS >> } >> >> /* >> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S >> index bb950c896a67..1d3d3b599635 100644 >> --- a/arch/arm/kernel/vmlinux.lds.S >> +++ b/arch/arm/kernel/vmlinux.lds.S >> @@ -149,7 +149,7 @@ SECTIONS >> _end = .; >> >> STABS_DEBUG >> - ELF_DETAILS >> + ARM_DETAILS >> } >> >> #ifdef CONFIG_STRICT_KERNEL_RWX >> -- >> 2.25.1 >> _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel