[PATCH v2] ARM: Add support for STACKLEAK gcc plugin

[Linus Walleij]

On Mon, Jun 24, 2024 at 4:33 AM Jinjie Ruan <ruanjinjie at huawei.com> wrote:

> Add the STACKLEAK gcc plugin to arm32 by adding the helper used by
> stackleak common code: on_thread_stack(). It initialize the stack with the
> poison value before returning from system calls which improves the kernel
> security. Additionally, this disables the plugin in EFI stub code and
> decompress code, which are out of scope for the protection.
>
> Before the test on Qemu versatilepb board:
>         # echo STACKLEAK_ERASING  > /sys/kernel/debug/provoke-crash/DIRECT
>         lkdtm: Performing direct entry STACKLEAK_ERASING
>         lkdtm: XFAIL: stackleak is not supported on this arch (HAVE_ARCH_STACKLEAK=n)
>
> After:
>         # echo STACKLEAK_ERASING  > /sys/kernel/debug/provoke-crash/DIRECT
>         lkdtm: Performing direct entry STACKLEAK_ERASING
>         lkdtm: stackleak stack usage:
>           high offset: 80 bytes
>           current:     280 bytes
>           lowest:      696 bytes
>           tracked:     696 bytes
>           untracked:   192 bytes
>           poisoned:    7220 bytes
>           low offset:  4 bytes
>         lkdtm: OK: the rest of the thread stack is properly erased
>
> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
> Acked-by: Ard Biesheuvel <ardb at kernel.org>

Reviewed-by: Linus Walleij <linus.walleij at linaro.org>

I was digging around to see if this would interfere with BPF
trampolines, but the
BPF code seems so generic that I assume it already takes stackleak into account.

Yours,
Linus Walleij