linux-kernel - Re: [PATCH] mtd: diskonchip: work around ubsan link failure

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Message-Id: <20240409064128.91899-1-miquel.raynal@bootlin.com>
Date: Tue,  9 Apr 2024 08:41:27 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Arnd Bergmann <arnd@...nel.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>
Cc: Arnd Bergmann <arnd@...db.de>,
	stable@...r.kernel.org,
	Dinghao Liu <dinghao.liu@....edu.cn>,
	linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: diskonchip: work around ubsan link failure

On Fri, 2024-04-05 at 14:30:04 UTC, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> I ran into a randconfig build failure with UBSAN using gcc-13.2:
> 
> arm-linux-gnueabi-ld: error: unplaced orphan section `.bss..Lubsan_data31' from `drivers/mtd/nand/raw/diskonchip.o'
> 
> I'm not entirely sure what is going on here, but I suspect this has something
> to do with the check for the end of the doc_locations[] array that contains
> an (unsigned long)0xffffffff element, which is compared against the signed
> (int)0xffffffff. If this is the case, we should get a runtime check for
> undefined behavior, but we instead get an unexpected build-time error.
> 
> I would have expected this to work fine on 32-bit architectures despite the
> signed integer overflow, though on 64-bit architectures this likely won't
> ever work.
> 
> Changing the contition to instead check for the size of the array makes the
> code safe everywhere and avoids the ubsan check that leads to the link
> error. The loop code goes back to before 2.6.12.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel