Re: [PATCH] interconnect: qcom: icc-rpm: Set the count member before accessing the flex array

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Dec 04, 2024 at 12:33:34AM +0200, djakov@kernel.org wrote:
> From: Georgi Djakov <djakov@kernel.org>
> 
> The following UBSAN error is reported during boot on the db410c board on
> a clang-19 build:
> 
> Internal error: UBSAN: array index out of bounds: 00000000f2005512 [#1] PREEMPT SMP
> ...
> pc : qnoc_probe+0x5f8/0x5fc
> ...

Really happy to see more coverage of real hardware with compilers that
support __counted_by() so that we can start getting these addressed,
thanks for this!

> The cause of the error is that the counter member was not set before
> accessing the annotated flexible array member, but after that. Fix this
> by initializing it earlier.
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Closes: https://lore.kernel.org/r/CA+G9fYs+2mBz1y2dAzxkj9-oiBJ2Acm1Sf1h2YQ3VmBqj_VX2g@mail.gmail.com
> Fixes: dd4904f3b924 ("interconnect: qcom: Annotate struct icc_onecell_data with __counted_by")

Guess Kees missed one :)

> Signed-off-by: Georgi Djakov <djakov@kernel.org>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

This is exactly the thing that __builtin_counted_by_ref() is trying to
address, as these assignments happen right after the allocation:

https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fcounted_005fby_005fref

> ---
>  drivers/interconnect/qcom/icc-rpm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/interconnect/qcom/icc-rpm.c b/drivers/interconnect/qcom/icc-rpm.c
> index a8ed435f696c..ea1042d38128 100644
> --- a/drivers/interconnect/qcom/icc-rpm.c
> +++ b/drivers/interconnect/qcom/icc-rpm.c
> @@ -503,6 +503,7 @@ int qnoc_probe(struct platform_device *pdev)
>  			    GFP_KERNEL);
>  	if (!data)
>  		return -ENOMEM;
> +	data->num_nodes = num_nodes;
>  
>  	qp->num_intf_clks = cd_num;
>  	for (i = 0; i < cd_num; i++)
> @@ -597,7 +598,6 @@ int qnoc_probe(struct platform_device *pdev)
>  
>  		data->nodes[i] = node;
>  	}
> -	data->num_nodes = num_nodes;
>  
>  	clk_bulk_disable_unprepare(qp->num_intf_clks, qp->intf_clks);
>