linux-kernel - [PATCH 02/14] powerpc/8xx: Fix kernel vs user address comparison

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Message-ID: <3f574c9845ff0a023b46cb4f38d2c45aecd769bd.1724173828.git.christophe.leroy@csgroup.eu>
Date: Tue, 20 Aug 2024 19:23:46 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: CASAUBON Jean Michel <jean-michel.casaubon@...soprasteria.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Naveen N Rao <naveen@...nel.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 02/14] powerpc/8xx: Fix kernel vs user address comparison

Since commit 9132a2e82adc ("powerpc/8xx: Define a MODULE area below
kernel text"), module exec space is below PAGE_OFFSET so not only
space above PAGE_OFFSET, but space above TASK_SIZE need to be seen
as kernel space.

Until now the problem went undetected because by default TASK_SIZE
is 0x8000000 which means address space is determined by just
checking upper address bit. But when TASK_SIZE is over 0x80000000,
PAGE_OFFSET is used for comparison, leading to thinking module
addresses are part of user space.

Fix it by using TASK_SIZE instead of PAGE_OFFSET for address
comparison.

Fixes: 9132a2e82adc ("powerpc/8xx: Define a MODULE area below kernel text")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/head_8xx.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index ac74321b1192..c955a8196d55 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -41,12 +41,12 @@
 #include "head_32.h"
 
 .macro compare_to_kernel_boundary scratch, addr
-#if CONFIG_TASK_SIZE <= 0x80000000 && CONFIG_PAGE_OFFSET >= 0x80000000
+#if CONFIG_TASK_SIZE <= 0x80000000 && MODULES_VADDR >= 0x80000000
 /* By simply checking Address >= 0x80000000, we know if its a kernel address */
 	not.	\scratch, \addr
 #else
 	rlwinm	\scratch, \addr, 16, 0xfff8
-	cmpli	cr0, \scratch, PAGE_OFFSET@h
+	cmpli	cr0, \scratch, TASK_SIZE@h
 #endif
 .endm
 
@@ -404,7 +404,7 @@ FixupDAR:/* Entry point for dcbx workaround. */
 	mfspr	r10, SPRN_SRR0
 	mtspr	SPRN_MD_EPN, r10
 	rlwinm	r11, r10, 16, 0xfff8
-	cmpli	cr1, r11, PAGE_OFFSET@h
+	cmpli	cr1, r11, TASK_SIZE@h
 	mfspr	r11, SPRN_M_TWB	/* Get level 1 table */
 	blt+	cr1, 3f
 
-- 
2.44.0