kasan, arm64: don't tag executable vmalloc allocations

Besides asking vmalloc memory to be executable via the prot argument of
__vmalloc_node_range() (see the previous patch), the kernel can skip that
bit and instead mark memory as executable via set_memory_x().

Once tag-based KASAN modes start tagging vmalloc allocations, executing
code from such allocations will lead to the PC register getting a tag,
which is not tolerated by the kernel.

Generic kernel code typically allocates memory via module_alloc() if it
intends to mark memory as executable.  (On arm64 module_alloc() uses
__vmalloc_node_range() without setting the executable bit).

Thus, reset pointer tags of pointers returned from module_alloc().

However, on arm64 there's an exception: the eBPF subsystem.  Instead of
using module_alloc(), it uses vmalloc() (via bpf_jit_alloc_exec()) to
allocate its JIT region.

Thus, reset pointer tags of pointers returned from bpf_jit_alloc_exec().

Resetting tags for these pointers results in untagged pointers being
passed to set_memory_x().  This causes conflicts in arithmetic checks in
change_memory_common(), as vm_struct->addr pointer returned by
find_vm_area() is tagged.

Reset pointer tag of find_vm_area(addr)->addr in change_memory_common().

Link: https://lkml.kernel.org/r/b7b2595423340cd7d76b770e5d519acf3b72f0ab.1643047180.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm64/kernel/module.c

@@ -63,7 +63,8 @@ void *module_alloc(unsigned long size)
 		return NULL;
 	}
 
-	return p;
+	/* Memory is intended to be executable, reset the pointer tag. */
+	return kasan_reset_tag(p);
 }
 
 enum aarch64_reloc_op {

arch/arm64/mm/pageattr.c

@@ -85,7 +85,7 @@ static int change_memory_common(unsigned long addr, int numpages,
 	 */
 	area = find_vm_area((void *)addr);
 	if (!area ||
-	    end > (unsigned long)area->addr + area->size ||
+	    end > (unsigned long)kasan_reset_tag(area->addr) + area->size ||
 	    !(area->flags & VM_ALLOC))
 		return -EINVAL;
 

arch/arm64/net/bpf_jit_comp.c

@@ -1304,7 +1304,8 @@ u64 bpf_jit_alloc_exec_limit(void)
 
 void *bpf_jit_alloc_exec(unsigned long size)
 {
-	return vmalloc(size);
+	/* Memory is intended to be executable, reset the pointer tag. */
+	return kasan_reset_tag(vmalloc(size));
 }
 
 void bpf_jit_free_exec(void *addr)