linux-kernel - [PATCH 4.19 475/639] x86/pgtable/32: Fix LOWMEM

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Date:   Fri, 24 Jan 2020 10:30:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 475/639] x86/pgtable/32: Fix LOWMEM_PAGES constant

From: Arnd Bergmann <arnd@...db.de>

[ Upstream commit 26515699863d68058e290e18e83f444925920be5 ]

clang points out that the computation of LOWMEM_PAGES causes a signed
integer overflow on 32-bit x86:

arch/x86/kernel/head32.c:83:20: error: signed shift result (0x100000000) requires 34 bits to represent, but 'int' only has 32 bits [-Werror,-Wshift-overflow]
                (PAGE_TABLE_SIZE(LOWMEM_PAGES) << PAGE_SHIFT);
                                 ^~~~~~~~~~~~
arch/x86/include/asm/pgtable_32.h:109:27: note: expanded from macro 'LOWMEM_PAGES'
 #define LOWMEM_PAGES ((((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT))
                         ~^ ~~
arch/x86/include/asm/pgtable_32.h:98:34: note: expanded from macro 'PAGE_TABLE_SIZE'
 #define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)

Use the _ULL() macro to make it a 64-bit constant.

Fixes: 1e620f9b23e5 ("x86/boot/32: Convert the 32-bit pgtable setup code from assembly to C")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/20190710130522.1802800-1-arnd@arndb.de
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/include/asm/pgtable_32.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable_32.h b/arch/x86/include/asm/pgtable_32.h
index b3ec519e39827..71e1df8601765 100644
--- a/arch/x86/include/asm/pgtable_32.h
+++ b/arch/x86/include/asm/pgtable_32.h
@@ -106,6 +106,6 @@ do {						\
  * with only a host target support using a 32-bit type for internal
  * representation.
  */
-#define LOWMEM_PAGES ((((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT))
+#define LOWMEM_PAGES ((((_ULL(2)<<31) - __PAGE_OFFSET) >> PAGE_SHIFT))
 
 #endif /* _ASM_X86_PGTABLE_32_H */
-- 
2.20.1