linux-hardening - Re: [PATCH] mailbox: zynqmp: Annotate struct zynqmp_ipi_pdata with __counted

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Date: Tue, 3 Oct 2023 15:56:57 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Jassi Brar <jassisinghbrar@...il.com>, Michal Simek <michal.simek@....com>, 
	linux-arm-kernel@...ts.infradead.org, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] mailbox: zynqmp: Annotate struct zynqmp_ipi_pdata with __counted_by

On Fri, Sep 22, 2023 at 10:54 AM Kees Cook <keescook@...omium.org> wrote:
>
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct zynqmp_ipi_pdata.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>
> Cc: Jassi Brar <jassisinghbrar@...il.com>
> Cc: Michal Simek <michal.simek@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---

Great patch! Crucially, the count is _correctly_ assigned
to before the flexible array member is accessed.

Reviewed-by: Justin Stitt <justinstitt@...gle.com>

>  drivers/mailbox/zynqmp-ipi-mailbox.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mailbox/zynqmp-ipi-mailbox.c b/drivers/mailbox/zynqmp-ipi-mailbox.c
> index e4fcac97dbfa..7fa533e80dd9 100644
> --- a/drivers/mailbox/zynqmp-ipi-mailbox.c
> +++ b/drivers/mailbox/zynqmp-ipi-mailbox.c
> @@ -108,7 +108,7 @@ struct zynqmp_ipi_pdata {
>         unsigned int method;
>         u32 local_id;
>         int num_mboxes;
> -       struct zynqmp_ipi_mbox ipi_mboxes[];
> +       struct zynqmp_ipi_mbox ipi_mboxes[] __counted_by(num_mboxes);
>  };
>
>  static struct device_driver zynqmp_ipi_mbox_driver = {
> --
> 2.34.1
>
>
Thanks
Justin