Re: [PATCH] virt: acrn: Annotate struct vm_memory_region_batch with __counted_by

From: Gustavo A. R. Silva
Date: Sat Sep 23 2023 - 13:43:57 EST




On 9/22/23 11:51, Kees Cook wrote:
Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct vm_memory_region_batch.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Fei Li <fei1.li@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks
--
Gustavo

---
drivers/virt/acrn/acrn_drv.h | 2 +-
drivers/virt/acrn/mm.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/virt/acrn/acrn_drv.h b/drivers/virt/acrn/acrn_drv.h
index 5663c17ad37c..fb8438094f6f 100644
--- a/drivers/virt/acrn/acrn_drv.h
+++ b/drivers/virt/acrn/acrn_drv.h
@@ -60,7 +60,7 @@ struct vm_memory_region_batch {
u16 reserved[3];
u32 regions_num;
u64 regions_gpa;
- struct vm_memory_region_op regions_op[];
+ struct vm_memory_region_op regions_op[] __counted_by(regions_num);
};
/**
diff --git a/drivers/virt/acrn/mm.c b/drivers/virt/acrn/mm.c
index b4ad8d452e9a..fa5d9ca6be57 100644
--- a/drivers/virt/acrn/mm.c
+++ b/drivers/virt/acrn/mm.c
@@ -250,11 +250,11 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
ret = -ENOMEM;
goto unmap_kernel_map;
}
+ regions_info->regions_num = nr_regions;
/* Fill each vm_memory_region_op */
vm_region = regions_info->regions_op;
regions_info->vmid = vm->vmid;
- regions_info->regions_num = nr_regions;
regions_info->regions_gpa = virt_to_phys(vm_region);
user_vm_pa = memmap->user_vm_pa;
i = 0;