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From: Atish Patra <atish.patra@wdc.com>
To: linux-kernel@vger.kernel.org
Cc: Atish Patra <atish.patra@wdc.com>, Jim Wilson <jimw@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Anup Patel <anup@brainfault.org>,
	Ard Biesheuvel <ardb@kernel.org>, Borislav Petkov <bp@suse.de>,
	Greentime Hu <greentime.hu@sifive.com>,
	Kees Cook <keescook@chromium.org>,
	linux-riscv@lists.infradead.org,
	Michel Lespinasse <walken@google.com>,
	Mike Rapoport <rppt@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Zong Li <zong.li@sifive.com>
Subject: [PATCH v2 4/6] RISC-V: Align the .init.text section
Date: Mon, 26 Oct 2020 16:02:52 -0700	[thread overview]
Message-ID: <20201026230254.911912-5-atish.patra@wdc.com> (raw)
In-Reply-To: <20201026230254.911912-1-atish.patra@wdc.com>

In order to improve kernel text protection, we need separate .init.text/
.init.data/.text in separate sections. However, RISC-V linker relaxation
code is not aware of any alignment between sections. As a result, it may
relax any RISCV_CALL relocations between sections to JAL without realizing
that an inter section alignment may move the address farther. That may
lead to a relocation truncated fit error. However, linker relaxation code
is aware of the individual section alignments.

The detailed discussion on this issue can be found here.
https://github.com/riscv/riscv-gnu-toolchain/issues/738

Keep the .init.text section aligned so that linker relaxation will take
that as a hint while relaxing inter section calls.
Here are the code size changes for each section because of this change.

section         change in size (in bytes)
  .head.text      +4
  .text           +40
  .init.text      +6530
  .exit.text      +84

The only significant increase in size happened for .init.text because
all intra relocations also use 2MB alignment.

Suggested-by: Jim Wilson <jimw@sifive.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
 arch/riscv/kernel/vmlinux.lds.S | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 3ffbd6cbdb86..cacd7898ba7f 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -30,7 +30,13 @@ SECTIONS
 	. = ALIGN(PAGE_SIZE);
 
 	__init_begin = .;
-	INIT_TEXT_SECTION(PAGE_SIZE)
+	__init_text_begin = .;
+	.init.text : AT(ADDR(.init.text) - LOAD_OFFSET) ALIGN(SECTION_ALIGN) { \
+		_sinittext = .;						\
+		INIT_TEXT						\
+		_einittext = .;						\
+	}
+
 	. = ALIGN(8);
 	__soc_early_init_table : {
 		__soc_early_init_table_start = .;
-- 
2.25.1


WARNING: multiple messages have this Message-ID (diff)
From: Atish Patra <atish.patra@wdc.com>
To: linux-kernel@vger.kernel.org
Cc: Albert Ou <aou@eecs.berkeley.edu>,
	Kees Cook <keescook@chromium.org>,
	Anup Patel <anup@brainfault.org>,
	linux-riscv@lists.infradead.org,
	Atish Patra <atish.patra@wdc.com>,
	Palmer Dabbelt <palmer@dabbelt.com>, Zong Li <zong.li@sifive.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Greentime Hu <greentime.hu@sifive.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@suse.de>,
	Michel Lespinasse <walken@google.com>,
	Ard Biesheuvel <ardb@kernel.org>, Mike Rapoport <rppt@kernel.org>,
	Jim Wilson <jimw@sifive.com>
Subject: [PATCH v2 4/6] RISC-V: Align the .init.text section
Date: Mon, 26 Oct 2020 16:02:52 -0700	[thread overview]
Message-ID: <20201026230254.911912-5-atish.patra@wdc.com> (raw)
In-Reply-To: <20201026230254.911912-1-atish.patra@wdc.com>

In order to improve kernel text protection, we need separate .init.text/
.init.data/.text in separate sections. However, RISC-V linker relaxation
code is not aware of any alignment between sections. As a result, it may
relax any RISCV_CALL relocations between sections to JAL without realizing
that an inter section alignment may move the address farther. That may
lead to a relocation truncated fit error. However, linker relaxation code
is aware of the individual section alignments.

The detailed discussion on this issue can be found here.
https://github.com/riscv/riscv-gnu-toolchain/issues/738

Keep the .init.text section aligned so that linker relaxation will take
that as a hint while relaxing inter section calls.
Here are the code size changes for each section because of this change.

section         change in size (in bytes)
  .head.text      +4
  .text           +40
  .init.text      +6530
  .exit.text      +84

The only significant increase in size happened for .init.text because
all intra relocations also use 2MB alignment.

Suggested-by: Jim Wilson <jimw@sifive.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
 arch/riscv/kernel/vmlinux.lds.S | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 3ffbd6cbdb86..cacd7898ba7f 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -30,7 +30,13 @@ SECTIONS
 	. = ALIGN(PAGE_SIZE);
 
 	__init_begin = .;
-	INIT_TEXT_SECTION(PAGE_SIZE)
+	__init_text_begin = .;
+	.init.text : AT(ADDR(.init.text) - LOAD_OFFSET) ALIGN(SECTION_ALIGN) { \
+		_sinittext = .;						\
+		INIT_TEXT						\
+		_einittext = .;						\
+	}
+
 	. = ALIGN(8);
 	__soc_early_init_table : {
 		__soc_early_init_table_start = .;
-- 
2.25.1


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  parent reply	other threads:[~2020-10-26 23:03 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 23:02 [PATCH v2 0/6] Improve kernel section protections Atish Patra
2020-10-26 23:02 ` Atish Patra
2020-10-26 23:02 ` [PATCH v2 1/6] RISC-V: Move __start_kernel to .head.text Atish Patra
2020-10-26 23:02   ` Atish Patra
2020-10-26 23:02 ` [PATCH v2 2/6] RISC-V: Initialize SBI early Atish Patra
2020-10-26 23:02   ` Atish Patra
2020-10-27 10:04   ` Mike Rapoport
2020-10-27 10:04     ` Mike Rapoport
2020-10-27 18:38     ` Atish Patra
2020-10-27 18:38       ` Atish Patra
2020-10-26 23:02 ` [PATCH v2 3/6] RISC-V: Enforce protections for kernel sections early Atish Patra
2020-10-26 23:02   ` Atish Patra
2020-10-27 10:00   ` Mike Rapoport
2020-10-27 10:00     ` Mike Rapoport
2020-10-27 18:38     ` Atish Patra
2020-10-27 18:38       ` Atish Patra
2020-10-26 23:02 ` Atish Patra [this message]
2020-10-26 23:02   ` [PATCH v2 4/6] RISC-V: Align the .init.text section Atish Patra
2020-10-26 23:02 ` [PATCH v2 5/6] RISC-V: Protect .init.text & .init.data Atish Patra
2020-10-26 23:02   ` Atish Patra
2020-10-27 10:45   ` Mike Rapoport
2020-10-27 10:45     ` Mike Rapoport
2020-10-29 19:21     ` Atish Patra
2020-10-29 19:21       ` Atish Patra
2020-10-30  8:49       ` Mike Rapoport
2020-10-30  8:49         ` Mike Rapoport
2020-10-30 20:29         ` Atish Patra
2020-10-30 20:29           ` Atish Patra
2020-10-26 23:02 ` [PATCH v2 6/6] RISC-V: Move dynamic relocation section under __init Atish Patra
2020-10-26 23:02   ` Atish Patra

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