linux-kernel - [PATCH v4 36/45] powerpc/mm: Don't be too strict with

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Message-Id: <8c4a0d89d944eed984dd941e509614031a5ace2b.1589866984.git.christophe.leroy@csgroup.eu>
Date:   Tue, 19 May 2020 05:49:19 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v4 36/45] powerpc/mm: Don't be too strict with _etext
 alignment on PPC32

Similar to PPC64, accept to map RO data as ROX as a trade off between
between security and memory usage.

Having RO data executable is not a high risk as RO data can't be
modified to forge an exploit.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/Kconfig              | 26 --------------------------
 arch/powerpc/kernel/vmlinux.lds.S |  3 +--
 2 files changed, 1 insertion(+), 28 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1d4ef4f27dec..d147d379b1b9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -778,32 +778,6 @@ config THREAD_SHIFT
 	  Used to define the stack size. The default is almost always what you
 	  want. Only change this if you know what you are doing.
 
-config ETEXT_SHIFT_BOOL
-	bool "Set custom etext alignment" if STRICT_KERNEL_RWX && \
-					     (PPC_BOOK3S_32 || PPC_8xx)
-	depends on ADVANCED_OPTIONS
-	help
-	  This option allows you to set the kernel end of text alignment. When
-	  RAM is mapped by blocks, the alignment needs to fit the size and
-	  number of possible blocks. The default should be OK for most configs.
-
-	  Say N here unless you know what you are doing.
-
-config ETEXT_SHIFT
-	int "_etext shift" if ETEXT_SHIFT_BOOL
-	range 17 28 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
-	range 19 23 if STRICT_KERNEL_RWX && PPC_8xx
-	default 17 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
-	default 19 if STRICT_KERNEL_RWX && PPC_8xx
-	default PPC_PAGE_SHIFT
-	help
-	  On Book3S 32 (603+), IBATs are used to map kernel text.
-	  Smaller is the alignment, greater is the number of necessary IBATs.
-
-	  On 8xx, large pages (512kb or 8M) are used to map kernel linear
-	  memory. Aligning to 8M reduces TLB misses as only 8M pages are used
-	  in that case.
-
 config DATA_SHIFT_BOOL
 	bool "Set custom data alignment" if STRICT_KERNEL_RWX && \
 					    (PPC_BOOK3S_32 || PPC_8xx)
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 31a0f201fb6f..54f23205c2b9 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -15,7 +15,6 @@
 #include <asm/thread_info.h>
 
 #define STRICT_ALIGN_SIZE	(1 << CONFIG_DATA_SHIFT)
-#define ETEXT_ALIGN_SIZE	(1 << CONFIG_ETEXT_SHIFT)
 
 ENTRY(_stext)
 
@@ -116,7 +115,7 @@ SECTIONS
 
 	} :text
 
-	. = ALIGN(ETEXT_ALIGN_SIZE);
+	. = ALIGN(PAGE_SIZE);
 	_etext = .;
 	PROVIDE32 (etext = .);
 
-- 
2.25.0