linux-kernel - [PATCH 5.4 108/142] x86/syscalls: Revert "x86/syscalls: Make __X32_SYSCALL

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Date:   Mon,  1 Jun 2020 19:54:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thorsten Glaser <t.glaser@...ent.de>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, stable@...nel.org
Subject: [PATCH 5.4 108/142] x86/syscalls: Revert "x86/syscalls: Make __X32_SYSCALL_BIT be unsigned long"

From: Andy Lutomirski <luto@...nel.org>

commit 700d3a5a664df267f01ec8887fd2d8ff98f67e7f upstream.

Revert

  45e29d119e99 ("x86/syscalls: Make __X32_SYSCALL_BIT be unsigned long")

and add a comment to discourage someone else from making the same
mistake again.

It turns out that some user code fails to compile if __X32_SYSCALL_BIT
is unsigned long. See, for example [1] below.

 [ bp: Massage and do the same thing in the respective tools/ header. ]

Fixes: 45e29d119e99 ("x86/syscalls: Make __X32_SYSCALL_BIT be unsigned long")
Reported-by: Thorsten Glaser <t.glaser@...ent.de>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: stable@...nel.org
Link: [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=954294
Link: https://lkml.kernel.org/r/92e55442b744a5951fdc9cfee10badd0a5f7f828.1588983892.git.luto@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/include/uapi/asm/unistd.h       |   11 +++++++++--
 tools/arch/x86/include/uapi/asm/unistd.h |    2 +-
 2 files changed, 10 insertions(+), 3 deletions(-)

--- a/arch/x86/include/uapi/asm/unistd.h
+++ b/arch/x86/include/uapi/asm/unistd.h
@@ -2,8 +2,15 @@
 #ifndef _UAPI_ASM_X86_UNISTD_H
 #define _UAPI_ASM_X86_UNISTD_H
 
-/* x32 syscall flag bit */
-#define __X32_SYSCALL_BIT	0x40000000UL
+/*
+ * x32 syscall flag bit.  Some user programs expect syscall NR macros
+ * and __X32_SYSCALL_BIT to have type int, even though syscall numbers
+ * are, for practical purposes, unsigned long.
+ *
+ * Fortunately, expressions like (nr & ~__X32_SYSCALL_BIT) do the right
+ * thing regardless.
+ */
+#define __X32_SYSCALL_BIT	0x40000000
 
 #ifndef __KERNEL__
 # ifdef __i386__
--- a/tools/arch/x86/include/uapi/asm/unistd.h
+++ b/tools/arch/x86/include/uapi/asm/unistd.h
@@ -3,7 +3,7 @@
 #define _UAPI_ASM_X86_UNISTD_H
 
 /* x32 syscall flag bit */
-#define __X32_SYSCALL_BIT	0x40000000UL
+#define __X32_SYSCALL_BIT	0x40000000
 
 #ifndef __KERNEL__
 # ifdef __i386__