linux-kernel - [PATCH 4/7] riscv: drop the use of XIP_OFFSET in XIP_FIXUP_FLASH

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <a49044c3833e40546f35dd1f821a683e6f4dfc1f.1715286093.git.namcao@linutronix.de>
Date: Fri, 10 May 2024 08:28:42 +0200
From: Nam Cao <namcao@...utronix.de>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: Nam Cao <namcao@...utronix.de>
Subject: [PATCH 4/7] riscv: drop the use of XIP_OFFSET in XIP_FIXUP_FLASH_OFFSET

XIP_OFFSET is the hard-coded offset of writable data section within the
kernel.

By hard-coding this value, the read-only section of the kernel (which is
placed before the writable data section) is restricted in size.

As a preparation to remove this hard-coded macro XIP_OFFSET entirely, stop
using XIP_OFFSET in XIP_FIXUP_FLASH_OFFSET. Instead, use __data_loc and
_sdata to do the same thing.

While at it, also add a description for XIP_FIXUP_FLASH_OFFSET.

Signed-off-by: Nam Cao <namcao@...utronix.de>
---
 arch/riscv/include/asm/xip_fixup.h | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/xip_fixup.h b/arch/riscv/include/asm/xip_fixup.h
index 9ed2cfae09e0..f3d56299bc22 100644
--- a/arch/riscv/include/asm/xip_fixup.h
+++ b/arch/riscv/include/asm/xip_fixup.h
@@ -24,13 +24,21 @@
 	sub \reg, \reg, t0
 .endm
 .macro XIP_FIXUP_FLASH_OFFSET reg
+	/* In linker script, at the transition from read-only section to
+	 * writable section, the VMA is increased while LMA remains the same.
+	 * (See in linker script how _sdata, __data_loc and LOAD_OFFSET is
+	 * changed)
+	 *
+	 * Consequently, early during boot before MMU is up, the generated code
+	 * reads the "writable" section at wrong addresses, because VMA is used
+	 * by compiler to generate code, but the data is located in Flash using
+	 * LMA.
+	 */
+	la t0, _sdata
+	sub \reg, \reg, t0
 	la t0, __data_loc
-	REG_L t1, _xip_phys_offset
-	sub \reg, \reg, t1
 	add \reg, \reg, t0
 .endm
-
-_xip_phys_offset: .dword CONFIG_XIP_PHYS_ADDR + XIP_OFFSET
 #else
 .macro XIP_FIXUP_OFFSET reg
 .endm
-- 
2.39.2