linux-kernel - Re: [PATCH] firmware: arm_ffa: avoid string-fortify warningn in export

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Message-ID: <ZuG5VKBcbHN2kiut@bogus>
Date: Wed, 11 Sep 2024 16:37:56 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: "Arnd Bergmann" <arnd@...db.de>
Cc: "Arnd Bergmann" <arnd@...nel.org>,
	"Cristian Marussi" <cristian.marussi@....com>,
	"Jens Wiklander" <jens.wiklander@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firmware: arm_ffa: avoid string-fortify warningn in
 export_uuid()

On Wed, Sep 11, 2024 at 02:44:25PM +0000, Arnd Bergmann wrote:
> On Wed, Sep 11, 2024, at 14:14, Sudeep Holla wrote:
> > On Mon, Sep 09, 2024 at 11:09:24AM +0000, Arnd Bergmann wrote:
> >> From: Arnd Bergmann <arnd@...db.de>
> >> 
> >> Copying to a 16 byte structure into an 8-byte struct member
> >> causes a compile-time warning:
> >> 
> >> In file included from drivers/firmware/arm_ffa/driver.c:25:
> >> In function 'fortify_memcpy_chk',
> >>     inlined from 'export_uuid' at include/linux/uuid.h:88:2,
> >>     inlined from 'ffa_msg_send_direct_req2' at drivers/firmware/arm_ffa/driver.c:488:2:
> >> include/linux/fortify-string.h:571:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
> >>   571 |                         __write_overflow_field(p_size_field, size);
> >>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> 
> >> Use a union for the conversion instead and make sure the byte order
> >> is fixed in the process.
> >> 
> >
> > Thanks for spotting and fixing the issue. I tested enabling
> > CONFIG_FORTIFY_SOURCE but couldn't hit this with gcc 13 and clang 20
> 
> Unfortunately I also don't have a reproducer at the moment,
> but I know it was from a randconfig build with gcc-14.2. I tried
> another few hundred randconfigs now with my patch reverted but it
> didn't come back. I assume it only shows up in rare combinations
> of some options,
>

Oh OK.

> Do you have any additional information on the endianess question?
> Is this arm_ffa firmware code supposed to work with big-endian
> kernels?
>

I am trying to check if that is a requirement. Also the specification
doesn't have any specific mention about it. Since it executes on the same
AP cores as Linux in different EL, I assume the entire stack must be
running same endian-ness. I will check internally. Unlike SCMI, I haven't
tested FF-A with big-endian kernel so far.

> > Also do you want this sent as fix on top of my FF-A PR now or after -rc1 ?
> 
> Earlier would be better I think. I usually have one set of
> bugfixes before rc1 even if it doesn't make it into the
> first set of branches.
>

I will try to send earlier unless this endian-ness triggers more questions.
I will update here anyways.

-- 
Regards,
Sudeep