Re: [PATCH mm v4 32/39] kasan, arm64: don't tag executable vmalloc allocations

Catalin Marinas
2021-12-22T11:11:16Z

On Mon, Dec 20, 2021 at 11:02:04PM +0100, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.com>
>
> 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().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>