[PATCH 2/4] arm64: omit [_text, _stext) from permanent kernel mapping

[Will Deacon]

On Tue, Oct 27, 2020 at 08:32:07AM +0100, Ard Biesheuvel wrote:
> In a previous patch, we increased the size of the EFI PE/COFF header
> to 64 KB, which resulted in the _stext symbol to appear at a fixed
> offset of 64 KB into the image.
> 
> Since 64 KB is also the largest page size we support, this completely
> removes the need to map the first 64 KB of the kernel image, given that
> it only contains the arm64 Image header and the EFI header, none of which
> we ever access again after booting the kernel. More importantly, we should
> avoid an executable mapping of non-executable and not entirely predictable
> data, in the unlikely event that we emitted something that looks like an
> opcode that could be used as a gadget for speculative execution.
> 
> So let's limit the kernel mapping of .text to the [_stext, _etext) region,
> which matches the view of generic code (such as kallsyms) when it reasons
> about the boundaries of the kernel's .text section.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  arch/arm64/kernel/efi-header.S  |  7 -------
>  arch/arm64/kernel/setup.c       |  4 ++--
>  arch/arm64/kernel/vmlinux.lds.S |  2 +-
>  arch/arm64/mm/init.c            |  2 +-
>  arch/arm64/mm/mmu.c             | 10 +++++-----
>  5 files changed, 9 insertions(+), 16 deletions(-)

Acked-by: Will Deacon <will at kernel.org>

Will