[PATCH] x86-64: fix perms/range of vsyscall vma in /proc/*/maps

The final line of /proc/<pid>/maps on x86_64 for native 64-bit
tasks shows an incorrect ending address and incorrect permissions.  There
is only a single page mapped in this vsyscall region, and it is accessible
for both read and execute.

The patch below fixes this.  (Since 32-bit-compat tasks have a real vma
with correct perms/range, no change is necessary for that scenario.)

Before the patch, a "cat /proc/self/maps | tail -1" shows this:

        ffffffffff600000-ffffffffffe00000 ---p 00000000 [...]

After the patch, this is the output:

        ffffffffff600000-ffffffffff601000 r-xp 00000000 [...]

Signed-off-by: Ernie Petrides <petrides@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>

arch/x86_64/kernel/vsyscall.c

@@ -290,6 +290,7 @@ static void __init map_vsyscall(void)
 	extern char __vsyscall_0;
 	unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);
 
+	/* Note that VSYSCALL_MAPPED_PAGES must agree with the code below. */
 	__set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
 }
 

arch/x86_64/mm/init.c

@@ -730,14 +730,15 @@ static __init int x8664_sysctl_init(void)
 __initcall(x8664_sysctl_init);
 #endif
 
-/* A pseudo VMAs to allow ptrace access for the vsyscall page.   This only
+/* A pseudo VMA to allow ptrace access for the vsyscall page.  This only
    covers the 64bit vsyscall page now. 32bit has a real VMA now and does
    not need special handling anymore. */
 
 static struct vm_area_struct gate_vma = {
 	.vm_start = VSYSCALL_START,
-	.vm_end = VSYSCALL_END,
-	.vm_page_prot = PAGE_READONLY
+	.vm_end = VSYSCALL_START + (VSYSCALL_MAPPED_PAGES << PAGE_SHIFT),
+	.vm_page_prot = PAGE_READONLY_EXEC,
+	.vm_flags = VM_READ | VM_EXEC
 };
 
 struct vm_area_struct *get_gate_vma(struct task_struct *tsk)

include/asm-x86_64/vsyscall.h

@@ -10,6 +10,7 @@ enum vsyscall_num {
 #define VSYSCALL_START (-10UL << 20)
 #define VSYSCALL_SIZE 1024
 #define VSYSCALL_END (-2UL << 20)
+#define VSYSCALL_MAPPED_PAGES 1
 #define VSYSCALL_ADDR(vsyscall_nr) (VSYSCALL_START+VSYSCALL_SIZE*(vsyscall_nr))
 
 #ifdef __KERNEL__