[PATCH v6 26/39] kasan, vmalloc: unpoison VM_ALLOC pages after mapping

andrey.konovalov
2022-01-24T19:00:52Z

Make KASAN unpoison vmalloc mappings after they have been mapped in
when it's possible: for vmalloc() (indentified via VM_ALLOC) and
vm_map_ram().

The reasons for this are:

- For vmalloc() and vm_map_ram(): pages don't get unpoisoned in case
mapping them fails.
- For vmalloc(): HW_TAGS KASAN needs pages to be mapped to set tags via
kasan_unpoison_vmalloc().

As a part of these changes, the return value of __vmalloc_node_range()
is changed to area->addr. This is a non-functional change, as
__vmalloc_area_node() returns area->addr anyway.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

---

Changes v3->v4:
- Don't forget to save tagged addr to vm_struct->addr for VM_ALLOC
so that find_vm_area(addr)->addr == addr for vmalloc().
- Reword comments.
- Update patch description.

Changes v2->v3:
- Update patch description.
---
mm/vmalloc.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 92e635b7490c..b65adac1cd80 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2210,14 +2210,15 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
mem = (void *)addr;
}

- mem = kasan_unpoison_vmalloc(mem, size);
-
if (vmap_pages_range(addr, addr + size, PAGE_KERNEL,
pages, PAGE_SHIFT) < 0) {
vm_unmap_ram(mem, count);
return NULL;
}

+ /* Mark the pages as accessible, now that they are mapped. */
+ mem = kasan_unpoison_vmalloc(mem, size);
+
return mem;
}
EXPORT_SYMBOL(vm_map_ram);
@@ -2445,7 +2446,14 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,

setup_vmalloc_vm(area, va, flags, caller);

- area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);
+ /*
+ * Mark pages for non-VM_ALLOC mappings as accessible. Do it now as a
+ * best-effort approach, as they can be mapped outside of vmalloc code.
+ * For VM_ALLOC mappings, the pages are marked as accessible after
+ * getting mapped in __vmalloc_node_range().
+ */
+ if (!(flags & VM_ALLOC))
+ area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);

return area;
}
@@ -3055,7 +3063,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
const void *caller)
{
struct vm_struct *area;
- void *addr;
+ void *ret;
unsigned long real_size = size;
unsigned long real_align = align;
unsigned int shift = PAGE_SHIFT;
@@ -3117,10 +3125,13 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
prot = arch_vmap_pgprot_tagged(prot);

/* Allocate physical pages and map them into vmalloc space. */
- addr = __vmalloc_area_node(area, gfp_mask, prot, shift, node);
- if (!addr)
+ ret = __vmalloc_area_node(area, gfp_mask, prot, shift, node);
+ if (!ret)
goto fail;

+ /* Mark the pages as accessible, now that they are mapped. */
+ area->addr = kasan_unpoison_vmalloc(area->addr, real_size);
+
/*
* In this function, newly allocated vm_struct has VM_UNINITIALIZED
* flag. It means that vm_struct is not fully initialized.
@@ -3132,7 +3143,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
if (!(vm_flags & VM_DEFER_KMEMLEAK))
kmemleak_vmalloc(area, size, gfp_mask);

- return addr;
+ return area->addr;

fail:
if (shift > PAGE_SHIFT) {
@@ -3816,7 +3827,10 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
}
spin_unlock(&vmap_area_lock);

- /* mark allocated areas as accessible */
+ /*
+ * Mark allocated areas as accessible. Do it now as a best-effort
+ * approach, as they can be mapped outside of vmalloc code.
+ */
for (area = 0; area < nr_vms; area++)
vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr,
vms[area]->size);