[tip:x86/mm] x86/mm: Make mmap(MAP_32BIT) work correctly

[tip-bot for Dmitry Safonov]

Commit-ID:  3e6ef9c80946f781fc25e8490c9875b1d2b61158
Gitweb:     http://git.kernel.org/tip/3e6ef9c80946f781fc25e8490c9875b1d2b61158
Author:     Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
AuthorDate: Mon, 6 Mar 2017 17:17:20 +0300
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Mon, 13 Mar 2017 14:59:23 +0100

x86/mm: Make mmap(MAP_32BIT) work correctly

mmap(MAP_32BIT) is broken due to the dependency on the TIF_ADDR32 thread
flag.

For 64bit applications MAP_32BIT will force legacy bottom-up allocations and
the 1GB address space restriction even if the application issued a compat
syscall, which should not be subject of these restrictions.

For 32bit applications, which issue 64bit syscalls the newly introduced
mmap base separation into 64-bit and compat bases changed the behaviour
because now a 64-bit mapping is returned, but due to the TIF_ADDR32
dependency MAP_32BIT is ignored. Before the separation a 32-bit mapping was
returned, so the MAP_32BIT handling was irrelevant.

Replace the check for TIF_ADDR32 with a check for the compat syscall. That
solves both the 64-bit issuing a compat syscall and the 32-bit issuing a
64-bit syscall problems.

[ tglx: Massaged changelog ]

Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
Cc: 0x7f454c46@xxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170306141721.9188-5-dsafonov@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
 arch/x86/kernel/sys_x86_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index c54817b..63e89df 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -115,7 +115,7 @@ static unsigned long get_mmap_base(int is_legacy)
 static void find_start_end(unsigned long flags, unsigned long *begin,
 			   unsigned long *end)
 {
-	if (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT)) {
+	if (!in_compat_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
@@ -191,7 +191,7 @@ 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 (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT))
+	if (!in_compat_syscall() && (flags & MAP_32BIT))
 		goto bottomup;
 
 	/* requesting a specific address */