[PATCH RFC v2 17/29] mm: asi: Map vmalloc/vmap data as nonsensitive

Brendan Jackman
2025-01-10T18:41:29Z

We add new VM flags for sensitive and global-nonsensitive, parallel to
the corresponding GFP flags.

__get_vm_area_node and friends will default to creating
global-nonsensitive VM areas, and vmap then calls asi_map as necessary.

__vmalloc_node_range has additional logic to check and set defaults for
the sensitivity of the underlying page allocation. It does this via an
initial __set_asi_flags call - note that it then calls
__get_vm_area_node which also calls __set_asi_flags. This second call
is a NOP.

By default, we mark the underlying page allocation as sensitive, even
if the VM area is global-nonsensitive. This is just an optimization to
avoid unnecessary asi_map etc, since presumably most code has no reason
to access vmalloc'd data through the direct map.

There are some details of the GFP-flag/VM-flag interaction that are not
really obvious, for example: what should happen when callers of
__vmalloc explicitly set GFP sensitivity flags? (That function has no VM
flags argument). For the moment let's just not block on that and focus
on adding the infrastructure, though.

At the moment, the high-level vmalloc APIs doesn't actually provide a
way to configure sensitivity, this commit just adds the infrastructure.
We'll have to decide how to expose this to allocation sites as we
implement more denylist logic. vmap does already allow configuring vm
flags.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
mm/vmalloc.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 8d260f2174fe664b54dcda054cb9759ae282bf03..00745edf0b2c5f4c769a46bdcf0872223de5299d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3210,6 +3210,7 @@ struct vm_struct *remove_vm_area(const void *addr)
{
struct vmap_area *va;
struct vm_struct *vm;
+ unsigned long vm_addr;

might_sleep();

@@ -3221,6 +3222,7 @@ struct vm_struct *remove_vm_area(const void *addr)
if (!va || !va->vm)
return NULL;
vm = va->vm;
+ vm_addr = (unsigned long) READ_ONCE(vm->addr);

debug_check_no_locks_freed(vm->addr, get_vm_area_size(vm));
debug_check_no_obj_freed(vm->addr, get_vm_area_size(vm));
@@ -3352,6 +3354,7 @@ void vfree(const void *addr)
addr);
return;
}
+ asi_unmap(ASI_GLOBAL_NONSENSITIVE, vm->addr, get_vm_area_size(vm));

if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS))
vm_reset_perms(vm);
@@ -3397,6 +3400,7 @@ void vunmap(const void *addr)
addr);
return;
}
+ asi_unmap(ASI_GLOBAL_NONSENSITIVE, vm->addr, get_vm_area_size(vm));
kfree(vm);
}
EXPORT_SYMBOL(vunmap);
@@ -3445,16 +3449,21 @@ void *vmap(struct page **pages, unsigned int count,

addr = (unsigned long)area->addr;
if (vmap_pages_range(addr, addr + size, pgprot_nx(prot),
- pages, PAGE_SHIFT) < 0) {
- vunmap(area->addr);
- return NULL;
- }
+ pages, PAGE_SHIFT) < 0)
+ goto err;
+
+ if (asi_map(ASI_GLOBAL_NONSENSITIVE, area->addr,
+ get_vm_area_size(area)))
+ goto err; /* The necessary asi_unmap() is in vunmap. */

if (flags & VM_MAP_PUT_PAGES) {
area->pages = pages;
area->nr_pages = count;
}
return area->addr;
+err:
+ vunmap(area->addr);
+ return NULL;
}
EXPORT_SYMBOL(vmap);

@@ -3711,6 +3720,10 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
goto fail;
}

+ if (asi_map(ASI_GLOBAL_NONSENSITIVE, area->addr,
+ get_vm_area_size(area)))
+ goto fail; /* The necessary asi_unmap() is in vfree. */
+
return area->addr;

fail:

--
2.47.1.613.gc27f4b7a9f-goog