[tip: x86/urgent] x86/syscalls: Revert "x86/syscalls: Make __X32_SYSCALL_BIT be unsigned long"

[tip-bot2 for Andy Lutomirski]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     700d3a5a664df267f01ec8887fd2d8ff98f67e7f
Gitweb:        https://git.kernel.org/tip/700d3a5a664df267f01ec8887fd2d8ff98f67e7f
Author:        Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate:    Fri, 08 May 2020 17:25:32 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 26 May 2020 16:42:43 +02:00

x86/syscalls: Revert "x86/syscalls: Make __X32_SYSCALL_BIT be unsigned long"

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@xxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: stable@xxxxxxxxxx
Link: [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=954294
Link: https://lkml.kernel.org/r/92e55442b744a5951fdc9cfee10badd0a5f7f828.1588983892.git.luto@xxxxxxxxxx
---
 arch/x86/include/uapi/asm/unistd.h       | 11 +++++++++--
 tools/arch/x86/include/uapi/asm/unistd.h |  2 +-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/uapi/asm/unistd.h b/arch/x86/include/uapi/asm/unistd.h
index 196fdd0..be5e2e7 100644
--- 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__
diff --git a/tools/arch/x86/include/uapi/asm/unistd.h b/tools/arch/x86/include/uapi/asm/unistd.h
index 196fdd0..30d7d04 100644
--- 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__