linux-kernel - Re: [PATCH] PCI: rcar-host: Avoid objtool no-cfi warning in rcar_pcie

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Message-ID: <CAMuHMdXZvoTyWcgRp6TnkybnKY4ekfO9aB33iumPVaR7wvEXkw@mail.gmail.com>
Date: Tue, 14 Oct 2025 09:16:58 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Marek Vasut <marek.vasut+renesas@...il.com>, 
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Manivannan Sadhasivam <mani@...nel.org>, Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Magnus Damm <magnus.damm@...il.com>, 
	linux-pci@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	kernel test robot <lkp@...el.com>, Kees Cook <kees@...nel.org>, 
	"Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH] PCI: rcar-host: Avoid objtool no-cfi warning in rcar_pcie_probe()

Hi Nathan,

On Mon, 13 Oct 2025 at 20:26, Nathan Chancellor <nathan@...nel.org> wrote:
> After commit 894af4a1cde6 ("objtool: Validate kCFI calls"), compile
> testing pcie-rcar-host.c with CONFIG_FINEIBT=y and CONFIG_OF=n results
> in a no-cfi objtool warning in rcar_pcie_probe():
>
>   $ cat allno.config
>   CONFIG_CFI=y
>   CONFIG_COMPILE_TEST=y
>   CONFIG_CPU_MITIGATIONS=y
>   CONFIG_GENERIC_PHY=y
>   CONFIG_MITIGATION_RETPOLINE=y
>   CONFIG_MODULES=y
>   CONFIG_PCI=y
>   CONFIG_PCI_MSI=y
>   CONFIG_PCIE_RCAR_HOST=y
>   CONFIG_X86_KERNEL_IBT=y
>
>   $ make -skj"$(nproc)" ARCH=x86_64 KCONFIG_ALLCONFIG=1 LLVM=1 clean allnoconfig vmlinux
>   vmlinux.o: warning: objtool: rcar_pcie_probe+0x191: no-cfi indirect call!
>
> When CONFIG_OF is unset, of_device_get_match_data() returns NULL, so
> LLVM knows this indirect call has no valid destination and drops the
> kCFI setup before the call, triggering the objtool check that makes sure
> all indirect calls have kCFI setup.
>
> Check that host->phy_init_fn is not NULL before calling it to avoid the
> warning.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202510092124.O2IX0Jek-lkp@intel.com/
> Reviewed-by: Kees Cook <kees@...nel.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks for your patch!

> ---
> Another alternative is to make this driver depend on CONFIG_OF since it
> clearly requires it but that would restrict compile testing so I went
> with this first.
> ---
>  drivers/pci/controller/pcie-rcar-host.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
> index 213028052aa5..15514c9c1927 100644
> --- a/drivers/pci/controller/pcie-rcar-host.c
> +++ b/drivers/pci/controller/pcie-rcar-host.c
> @@ -981,7 +981,7 @@ static int rcar_pcie_probe(struct platform_device *pdev)
>                 goto err_clk_disable;
>
>         host->phy_init_fn = of_device_get_match_data(dev);
> -       err = host->phy_init_fn(host);
> +       err = host->phy_init_fn ? host->phy_init_fn(host) : -ENODEV;
>         if (err) {
>                 dev_err(dev, "failed to init PCIe PHY\n");
>                 goto err_clk_disable;

I am afraid you're playing a big game of whack-a-mole, since we tend
to remove these checks, as they can never happen in practice (driver
is probed from DT only, and all entries in rcar_pcie_of_match[] have
a non-NULL .data member)...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds