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

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