[PATCH 4.4 54/74] vsyscall: Fix permissions for emulate mode with KAISER/PTI

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>

The backport of KAISER to 4.4 turned vsyscall emulate mode into native
mode.  Add a vsyscall_pgprot variable to hold the correct page
protections, like Borislav and Hugh did for 3.2 and 3.18.

Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/entry/vsyscall/vsyscall_64.c |    7 ++++---
 arch/x86/include/asm/vsyscall.h       |    1 +
 arch/x86/mm/kaiser.c                  |    2 +-
 3 files changed, 6 insertions(+), 4 deletions(-)

--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -46,6 +46,7 @@ static enum { EMULATE, NATIVE, NONE } vs
 #else
 	EMULATE;
 #endif
+unsigned long vsyscall_pgprot = __PAGE_KERNEL_VSYSCALL;
 
 static int __init vsyscall_setup(char *str)
 {
@@ -336,11 +337,11 @@ void __init map_vsyscall(void)
 	extern char __vsyscall_page;
 	unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 
+	if (vsyscall_mode != NATIVE)
+		vsyscall_pgprot = __PAGE_KERNEL_VVAR;
 	if (vsyscall_mode != NONE)
 		__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
-			     vsyscall_mode == NATIVE
-			     ? PAGE_KERNEL_VSYSCALL
-			     : PAGE_KERNEL_VVAR);
+			     __pgprot(vsyscall_pgprot));
 
 	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
 		     (unsigned long)VSYSCALL_ADDR);
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -13,6 +13,7 @@ extern void map_vsyscall(void);
  */
 extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
 extern bool vsyscall_enabled(void);
+extern unsigned long vsyscall_pgprot;
 #else
 static inline void map_vsyscall(void) {}
 static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -345,7 +345,7 @@ void __init kaiser_init(void)
 	if (vsyscall_enabled())
 		kaiser_add_user_map_early((void *)VSYSCALL_ADDR,
 					  PAGE_SIZE,
-					   __PAGE_KERNEL_VSYSCALL);
+					  vsyscall_pgprot);
 
 	for_each_possible_cpu(cpu) {
 		void *percpu_vaddr = __per_cpu_user_mapped_start +