The vast majority of virtual allocations in the vmalloc region are followed
by a guard page, which can help to avoid overruning on vma into another,
which may map a read-sensitive device.

This patch adds a guard page to the end of the kernel image mapping (i.e.
following the data/bss segments).

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <redacted>
Signed-off-by: Will Deacon <redacted>
---
 arch/arm64/mm/mmu.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 23c2d89a362e..f1eb15e0e864 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c

@@ -496,7 +496,7 @@ void mark_rodata_ro(void)

 static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,
                                      pgprot_t prot, struct vm_struct *vma,
-                                     int flags)
+                                     int flags, unsigned long vm_flags)
 {
        phys_addr_t pa_start = __pa_symbol(va_start);
        unsigned long size = va_end - va_start;

@@ -507,10 +507,13 @@ static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,
        __create_pgd_mapping(pgd, pa_start, (unsigned long)va_start, size, prot,
                             early_pgtable_alloc, flags);

+       if (!(vm_flags & VM_NO_GUARD))
+               size += PAGE_SIZE;
+
        vma->addr       = va_start;
        vma->phys_addr  = pa_start;
        vma->size       = size;
-       vma->flags      = VM_MAP;
+       vma->flags      = VM_MAP | vm_flags;
        vma->caller     = __builtin_return_address(0);

        vm_area_add_early(vma);

@@ -541,14 +544,15 @@ static void __init map_kernel(pgd_t *pgd)
         * Only rodata will be remapped with different permissions later on,
         * all other segments are allowed to use contiguous mappings.
         */
-       map_kernel_segment(pgd, _text, _etext, text_prot, &vmlinux_text, 0);
+       map_kernel_segment(pgd, _text, _etext, text_prot, &vmlinux_text, 0,
+                          VM_NO_GUARD);
        map_kernel_segment(pgd, __start_rodata, __inittext_begin, PAGE_KERNEL,
-                          &vmlinux_rodata, NO_CONT_MAPPINGS);
+                          &vmlinux_rodata, NO_CONT_MAPPINGS, VM_NO_GUARD);
        map_kernel_segment(pgd, __inittext_begin, __inittext_end, text_prot,
-                          &vmlinux_inittext, 0);
+                          &vmlinux_inittext, 0, VM_NO_GUARD);
        map_kernel_segment(pgd, __initdata_begin, __initdata_end, PAGE_KERNEL,
-                          &vmlinux_initdata, 0);
-       map_kernel_segment(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data, 0);
+                          &vmlinux_initdata, 0, VM_NO_GUARD);
+       map_kernel_segment(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data, 0, 0);

        if (!pgd_val(*pgd_offset_raw(pgd, FIXADDR_START))) {
                /*