Re: [PATCH v3] ARM: imx: Fix suspend/resume crash with Clang CFI

On Sat, Jul 18, 2026 at 4:14 AM Yo'av Moshe <[email protected]> wrote:
>
> Relocated suspend code in OCRAM lacks compiler-generated CFI type
> signatures. When CONFIG_CFI=y is active, the indirect call to
> imx6_suspend_in_ocram_fn triggers a strict CFI violation panic.
>
> To resolve this safely without reducing CFI protection scope:
> 1. Create a minimal wrapper function imx6_suspend_in_ocram annotated
>    with __nocfi to handle the unverified indirect call.
> 2. Remove the __nocfi annotation from the main imx6q_suspend_finish
>    function to preserve full CFI coverage for other indirect calls
>    in that scope (such as cpu_do_idle() and flush_cache_all()).
> 3. Mark global variables ccm_base, suspend_ocram_base, and the
>    imx6_suspend_in_ocram_fn pointer as __ro_after_init to prevent
>    them from being used as target vectors for CFI bypass exploits.
>
> Cc: [email protected]
> Signed-off-by: Yo'av Moshe <[email protected]>
> ---
> Tested on a Kobo Clara HD (i.MX6SLL SoC) running postmarketOS edge.
> Before this patch, suspending the device caused an immediate silent
> hang requiring a hard-reboot. With this patch applied, suspend and
> resume work successfully.
>
> Differences from v2:
> - Restrained __nocfi scope by adding a dedicated, minimal 1-line
>   wrapper function (imx6_suspend_in_ocram) for the OCRAM call,
>   avoiding disabling CFI checks for cpu_do_idle() and flush_cache_all().
> - Marked global pointers ccm_base and suspend_ocram_base as
>   __ro_after_init to fully neutralize Write-What-Where exploit bypasses.
>
>  arch/arm/mach-imx/pm-imx6.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/mach-imx/pm-imx6.c b/arch/arm/mach-imx/pm-imx6.c
> index a671ca498..3d5b960c5 100644
> --- a/arch/arm/mach-imx/pm-imx6.c
> +++ b/arch/arm/mach-imx/pm-imx6.c
> @@ -61,9 +61,9 @@
>  #define MX6Q_SUSPEND_OCRAM_SIZE                0x1000
>  #define MX6_MAX_MMDC_IO_NUM            33
>
> -static void __iomem *ccm_base;
> -static void __iomem *suspend_ocram_base;
> -static void (*imx6_suspend_in_ocram_fn)(void __iomem *ocram_vbase);
> +static void __iomem *ccm_base __ro_after_init;
> +static void __iomem *suspend_ocram_base __ro_after_init;
> +static void (*imx6_suspend_in_ocram_fn)(void __iomem *ocram_vbase) __ro_after_init;

Are we able to just put __nocfi on the declaration of
`imx6_suspend_in_ocram_fn`, rather than bother with a wrapper
(imx6_suspend_in_ocram)? I don't know if that works, but surely you
can test that quickly?

>
>  /*
>   * suspend ocram space layout:
> @@ -360,6 +360,11 @@ int imx6_set_lpm(enum mxc_cpu_pwr_mode mode)
>         return 0;
>  }
>
> +static void __nocfi imx6_suspend_in_ocram(void __iomem *ocram_vbase)
> +{
> +       imx6_suspend_in_ocram_fn(ocram_vbase);
> +}
> +
>  static int imx6q_suspend_finish(unsigned long val)
>  {
>         if (!imx6_suspend_in_ocram_fn) {
> @@ -374,7 +379,7 @@ static int imx6q_suspend_finish(unsigned long val)
>                 if (!((struct imx6_cpu_pm_info *)
>                         suspend_ocram_base)->l2_base.vbase)
>                         flush_cache_all();
> -               imx6_suspend_in_ocram_fn(suspend_ocram_base);
> +               imx6_suspend_in_ocram(suspend_ocram_base);
>         }
>
>         return 0;
> --
> 2.55.0
>


-- 
Thanks,
~Nick Desaulniers