On Mon, Dec 20, 2021 at 11:02:04PM +0100, andrey.konovalov@linux.dev wrote:

From: Andrey Konovalov <redacted>

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 <redacted>

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