linux-kernel - Re: [PATCH] ALSA: asihpi: work around clang-17+ false positive fortify-string warning

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Date: Wed, 28 Feb 2024 15:37:01 +0100
From: Takashi Iwai <tiwai@...e.de>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH] ALSA: asihpi: work around clang-17+ false positive fortify-string warning

On Wed, 28 Feb 2024 15:01:45 +0100,
Arnd Bergmann wrote:
> 
> From: Arnd Bergmann <arnd@...db.de>
> 
> One of the memory copies in this driver triggers a warning about a
> possible out of range access:
> 
> In file included from /home/arnd/arm-soc/sound/pci/asihpi/hpimsgx.c:13:
> /home/arnd/arm-soc/include/linux/fortify-string.h:553:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
>   553 |                         __write_overflow_field(p_size_field, size);
>       |                         ^

Hmm, I can't see the relevance of those messages with the code you
touched.  Do you have more info?

> Adding a range check avoids the problem, though I don't quite see
> why it warns in the first place if clang has no knowledge of the
> actual range of the type, or why I never saw the warning in previous
> randconfig tests.

It's indeed puzzling.  If it's really about adapter_prepare() call,
the caller is only HPIMSGX__init(), and there is already an assignment
with that index value beforehand:
  hpi_entry_points[hr.u.s.adapter_index] = entry_point_func;

and this array is also the size of HPI_MAX_ADAPTERS.  That is, the
same check should have caught here...


thanks,

Takashi

> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  sound/pci/asihpi/hpimsgx.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/sound/pci/asihpi/hpimsgx.c b/sound/pci/asihpi/hpimsgx.c
> index d0caef299481..4f245c3956b1 100644
> --- a/sound/pci/asihpi/hpimsgx.c
> +++ b/sound/pci/asihpi/hpimsgx.c
> @@ -576,6 +576,9 @@ static u16 adapter_prepare(u16 adapter)
>  	/* Open the adapter and streams */
>  	u16 i;
>  
> +	if (adapter >= ARRAY_SIZE(rESP_HPI_ADAPTER_OPEN))
> +		return 0;
> +
>  	/* call to HPI_ADAPTER_OPEN */
>  	hpi_init_message_response(&hm, &hr, HPI_OBJ_ADAPTER,
>  		HPI_ADAPTER_OPEN);
> -- 
> 2.39.2
>