arm64: allow vmalloc regions to be set with set_memory_*

The range of set_memory_* is currently restricted to the module address
range because of difficulties in breaking down larger block sizes.
vmalloc maps PAGE_SIZE pages so it is safe to use as well. Update the
function ranges and add a comment explaining why the range is restricted
the way it is.

Suggested-by: Laura Abbott <labbott@fedoraproject.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 19 insertions, 4 deletions

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index cf6240741134..0795c3a36d8f 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -14,6 +14,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/sched.h>
+#include <linux/vmalloc.h>
 
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
@@ -44,6 +45,7 @@ static int change_memory_common(unsigned long addr, int numpages,
         unsigned long end = start + size;
         int ret;
         struct page_change_data data;
+        struct vm_struct *area;
 
         if (!PAGE_ALIGNED(addr)) {
                 start &= PAGE_MASK;
@@ -51,10 +53,23 @@ static int change_memory_common(unsigned long addr, int numpages,
                 WARN_ON_ONCE(1);
         }
 
-        if (start < MODULES_VADDR || start >= MODULES_END)
-                return -EINVAL;
-
-        if (end < MODULES_VADDR || end >= MODULES_END)
+        /*
+         * Kernel VA mappings are always live, and splitting live section
+         * mappings into page mappings may cause TLB conflicts. This means
+         * we have to ensure that changing the permission bits of the range
+         * we are operating on does not result in such splitting.
+         *
+         * Let's restrict ourselves to mappings created by vmalloc (or vmap).
+         * Those are guaranteed to consist entirely of page mappings, and
+         * splitting is never needed.
+         *
+         * So check whether the [addr, addr + size) interval is entirely
+         * covered by precisely one VM area that has the VM_ALLOC flag set.
+         */
+        area = find_vm_area((void *)addr);
+        if (!area ||
+            end > (unsigned long)area->addr + area->size ||
+            !(area->flags & VM_ALLOC))
                 return -EINVAL;
 
         if (!numpages)