linux-kernel - [PATCH 1/2] powerpc/vdso: Fix VDSO data access when running in a non-root time namespace

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Message-ID: <700dbf296d02e32376329774be35cfbead08041d.1725611321.git.christophe.leroy@csgroup.eu>
Date: Fri,  6 Sep 2024 10:33:43 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "Jason A . Donenfeld" <Jason@...c4.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Naveen N Rao <naveen@...nel.org>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Andrei Vagin <avagin@...il.com>
Subject: [PATCH 1/2] powerpc/vdso: Fix VDSO data access when running in a non-root time namespace

When running in a non-root time namespace, the global VDSO data page
is replaced by a dedicated namespace data page and the global data
page is mapped next to it. Detailed explanations can be found at
commit 660fd04f9317 ("lib/vdso: Prepare for time namespace support").

When it happens, __kernel_get_syscall_map and __kernel_get_tbfreq
and __kernel_sync_dicache don't work anymore because they read 0
instead of the data they need.

To address that, clock_mode has to be read. When it is set to
VDSO_CLOCKMODE_TIMENS, it means it is a dedicated namespace data page
and the global data is located on the following page.

Add a macro called get_realdatapage which reads clock_mode and add
PAGE_SIZE to the pointer provided by get_datapage macro when
clock_mode is equal to VDSO_CLOCKMODE_TIMENS. Use this new macro
instead of get_datapage macro except for time functions as they handle
it internally.

Fixes: 74205b3fc2ef ("powerpc/vdso: Add support for time namespaces")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/include/asm/vdso_datapage.h | 15 +++++++++++++++
 arch/powerpc/kernel/asm-offsets.c        |  2 ++
 arch/powerpc/kernel/vdso/cacheflush.S    |  2 +-
 arch/powerpc/kernel/vdso/datapage.S      |  4 ++--
 4 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index e17500c5237e..248dee138f7b 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -113,6 +113,21 @@ extern struct vdso_arch_data *vdso_data;
 	addi	\ptr, \ptr, (_vdso_datapage - 999b)@l
 .endm
 
+#include <asm/asm-offsets.h>
+#include <asm/page.h>
+
+.macro get_realdatapage ptr scratch
+	get_datapage \ptr
+#ifdef CONFIG_TIME_NS
+	lwz	\scratch, VDSO_CLOCKMODE_OFFSET(\ptr)
+	xoris	\scratch, \scratch, VDSO_CLOCKMODE_TIMENS@h
+	xori	\scratch, \scratch, VDSO_CLOCKMODE_TIMENS@l
+	cntlzw	\scratch, \scratch
+	rlwinm	\scratch, \scratch, PAGE_SHIFT - 5, 1 << PAGE_SHIFT
+	add	\ptr, \ptr, \scratch
+#endif
+.endm
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index eedb2e04c785..131a8cc10dbe 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -347,6 +347,8 @@ int main(void)
 #else
 	OFFSET(CFG_SYSCALL_MAP32, vdso_arch_data, syscall_map);
 #endif
+	OFFSET(VDSO_CLOCKMODE_OFFSET, vdso_arch_data, data[0].clock_mode);
+	DEFINE(VDSO_CLOCKMODE_TIMENS, VDSO_CLOCKMODE_TIMENS);
 
 #ifdef CONFIG_BUG
 	DEFINE(BUG_ENTRY_SIZE, sizeof(struct bug_entry));
diff --git a/arch/powerpc/kernel/vdso/cacheflush.S b/arch/powerpc/kernel/vdso/cacheflush.S
index 0085ae464dac..3b2479bd2f9a 100644
--- a/arch/powerpc/kernel/vdso/cacheflush.S
+++ b/arch/powerpc/kernel/vdso/cacheflush.S
@@ -30,7 +30,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
 #ifdef CONFIG_PPC64
 	mflr	r12
   .cfi_register lr,r12
-	get_datapage	r10
+	get_realdatapage	r10, r11
 	mtlr	r12
   .cfi_restore	lr
 #endif
diff --git a/arch/powerpc/kernel/vdso/datapage.S b/arch/powerpc/kernel/vdso/datapage.S
index db8e167f0166..2b19b6201a33 100644
--- a/arch/powerpc/kernel/vdso/datapage.S
+++ b/arch/powerpc/kernel/vdso/datapage.S
@@ -28,7 +28,7 @@ V_FUNCTION_BEGIN(__kernel_get_syscall_map)
 	mflr	r12
   .cfi_register lr,r12
 	mr.	r4,r3
-	get_datapage	r3
+	get_realdatapage	r3, r11
 	mtlr	r12
 #ifdef __powerpc64__
 	addi	r3,r3,CFG_SYSCALL_MAP64
@@ -52,7 +52,7 @@ V_FUNCTION_BEGIN(__kernel_get_tbfreq)
   .cfi_startproc
 	mflr	r12
   .cfi_register lr,r12
-	get_datapage	r3
+	get_realdatapage	r3, r11
 #ifndef __powerpc64__
 	lwz	r4,(CFG_TB_TICKS_PER_SEC + 4)(r3)
 #endif
-- 
2.44.0