x86/compat: Adjust in_compat_syscall() to generic code under !COMPAT

The result of in_compat_syscall() can be pictured as:

x86 platform:
    ---------------------------------------------------
    |  Arch\syscall  |  64-bit  |   ia32   |   x32    |
    |-------------------------------------------------|
    |     x86_64     |  false   |   true   |   true   |
    |-------------------------------------------------|
    |      i686      |          |  <true>  |          |
    ---------------------------------------------------

Other platforms:
    -------------------------------------------
    |  Arch\syscall  |  64-bit  |   compat    |
    |-----------------------------------------|
    |     64-bit     |  false   |    true     |
    |-----------------------------------------|
    |    32-bit(?)   |          |   <false>   |
    -------------------------------------------

As seen, the result of in_compat_syscall() on generic 32-bit platform
differs from i686.

There is no reason for in_compat_syscall() == true on native i686.  It also
easy to misread code if the result on native 32-bit platform differs
between arches.

Because of that non arch-specific code has many places with:
    if (IS_ENABLED(CONFIG_COMPAT) && in_compat_syscall())
in different variations.

It looks-like the only non-x86 code which uses in_compat_syscall() not
under CONFIG_COMPAT guard is in amd/amdkfd. But according to the commit
a18069c132cb ("amdkfd: Disable support for 32-bit user processes"), it
actually should be disabled on native i686.

Rename in_compat_syscall() to in_32bit_syscall() for x86-specific code
and make in_compat_syscall() false under !CONFIG_COMPAT.

A follow on patch will clean up generic users which were forced to check
IS_ENABLED(CONFIG_COMPAT) with in_compat_syscall().

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-efi@vger.kernel.org
Cc: netdev@vger.kernel.org
Link: https://lkml.kernel.org/r/20181012134253.23266-2-dima@arista.com

1 files changed, 6 insertions, 5 deletions

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 6a78d4b36a79..f7476ce23b6e 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -105,7 +105,7 @@ out:
 static void find_start_end(unsigned long addr, unsigned long flags,
 		unsigned long *begin, unsigned long *end)
 {
-	if (!in_compat_syscall() && (flags & MAP_32BIT)) {
+	if (!in_32bit_syscall() && (flags & MAP_32BIT)) {
 		/* This is usually used needed to map code in small
 		   model, so it needs to be in the first 31bit. Limit
 		   it to that.  This means we need to move the
@@ -122,7 +122,7 @@ static void find_start_end(unsigned long addr, unsigned long flags,
 	}
 
 	*begin	= get_mmap_base(1);
-	if (in_compat_syscall())
+	if (in_32bit_syscall())
 		*end = task_size_32bit();
 	else
 		*end = task_size_64bit(addr > DEFAULT_MAP_WINDOW);
@@ -193,7 +193,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 		return addr;
 
 	/* for MAP_32BIT mappings we force the legacy mmap base */
-	if (!in_compat_syscall() && (flags & MAP_32BIT))
+	if (!in_32bit_syscall() && (flags & MAP_32BIT))
 		goto bottomup;
 
 	/* requesting a specific address */
@@ -217,9 +217,10 @@ get_unmapped_area:
 	 * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area
 	 * in the full address space.
 	 *
-	 * !in_compat_syscall() check to avoid high addresses for x32.
+	 * !in_32bit_syscall() check to avoid high addresses for x32
+	 * (and make it no op on native i386).
 	 */
-	if (addr > DEFAULT_MAP_WINDOW && !in_compat_syscall())
+	if (addr > DEFAULT_MAP_WINDOW && !in_32bit_syscall())
 		info.high_limit += TASK_SIZE_MAX - DEFAULT_MAP_WINDOW;
 
 	info.align_mask = 0;