Message-ID: <2025071313-zippy-boneless-da1c@gregkh>
Date: Sun, 13 Jul 2025 17:42:43 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: srini@...nel.org
Cc: linux-kernel@...r.kernel.org, "Michael C. Pratt" <mcpratt@...me>,
	INAGAKI Hiroshi <musashino.open@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] nvmem: layouts: u-boot-env: remove crc32 endianness
 conversion

On Sun, Jul 13, 2025 at 05:41:45PM +0200, Greg KH wrote:
> On Sat, Jul 12, 2025 at 07:17:26PM +0100, srini@...nel.org wrote:
> > From: "Michael C. Pratt" <mcpratt@...me>
> > 
> > On 11 Oct 2022, it was reported that the crc32 verification
> > of the u-boot environment failed only on big-endian systems
> > for the u-boot-env nvmem layout driver with the following error.
> > 
> >   Invalid calculated CRC32: 0x88cd6f09 (expected: 0x096fcd88)
> > 
> > This problem has been present since the driver was introduced,
> > and before it was made into a layout driver.
> > 
> > The suggested fix at the time was to use further endianness
> > conversion macros in order to have both the stored and calculated
> > crc32 values to compare always represented in the system's endianness.
> > This was not accepted due to sparse warnings
> > and some disagreement on how to handle the situation.
> > Later on in a newer revision of the patch, it was proposed to use
> > cpu_to_le32() for both values to compare instead of le32_to_cpu()
> > and store the values as __le32 type to remove compilation errors.
> > 
> > The necessity of this is based on the assumption that the use of crc32()
> > requires endianness conversion because the algorithm uses little-endian,
> > however, this does not prove to be the case and the issue is unrelated.
> > 
> > Upon inspecting the current kernel code,
> > there already is an existing use of le32_to_cpu() in this driver,
> > which suggests there already is special handling for big-endian systems,
> > however, it is big-endian systems that have the problem.
> > 
> > This, being the only functional difference between architectures
> > in the driver combined with the fact that the suggested fix
> > was to use the exact same endianness conversion for the values
> > brings up the possibility that it was not necessary to begin with,
> > as the same endianness conversion for two values expected to be the same
> > is expected to be equivalent to no conversion at all.
> > 
> > After inspecting the u-boot environment of devices of both endianness
> > and trying to remove the existing endianness conversion,
> > the problem is resolved in an equivalent way as the other suggested fixes.
> > 
> > Ultimately, it seems that u-boot is agnostic to endianness
> > at least for the purpose of environment variables.
> > In other words, u-boot reads and writes the stored crc32 value
> > with the same endianness that the crc32 value is calculated with
> > in whichever endianness a certain architecture runs on.
> > 
> > Therefore, the u-boot-env driver does not need to convert endianness.
> > Remove the usage of endianness macros in the u-boot-env driver,
> > and change the type of local variables to maintain the same return type.
> > 
> > If there is a special situation in the case of endianness,
> > it would be a corner case and should be handled by a unique "compatible".
> > 
> > Even though it is not necessary to use endianness conversion macros here,
> > it may be useful to use them in the future for consistent error printing.
> > 
> > Fixes: d5542923f200 ("nvmem: add driver handling U-Boot environment variables")
> 
> Note, this is a 6.1 commit id, but:
> 
> > Reported-by: INAGAKI Hiroshi <musashino.open@...il.com>
> > Link: https://lore.kernel.org/all/20221011024928.1807-1-musashino.open@gmail.com
> > Cc: stable@...r.kernel.org # 6.12.x
> > Cc: stable@...r.kernel.org # 6.6.x: f4cf4e5: Revert "nvmem: add new config option"
> > Cc: stable@...r.kernel.org # 6.6.x: 7f38b70: of: device: Export of_device_make_bus_id()
> > Cc: stable@...r.kernel.org # 6.6.x: 4a1a402: nvmem: Move of_nvmem_layout_get_container() in another header
> > Cc: stable@...r.kernel.org # 6.6.x: fc29fd8: nvmem: core: Rework layouts to become regular devices
> > Cc: stable@...r.kernel.org # 6.6.x: 0331c61: nvmem: core: Expose cells through sysfs
> > Cc: stable@...r.kernel.org # 6.6.x: 401df0d: nvmem: layouts: refactor .add_cells() callback arguments
> > Cc: stable@...r.kernel.org # 6.6.x: 6d0ca4a: nvmem: layouts: store owner from modules with nvmem_layout_driver_register()
> > Cc: stable@...r.kernel.org # 6.6.x: 5f15811: nvmem: layouts: add U-Boot env layout
> > Cc: stable@...r.kernel.org # 6.6.x
> 
> That's a load of (short) git ids for just 6.6.y?  What about 6.1.y?

And really, ALL of those commits are needed for this very tiny patch?
Reverting a config option?  sysfs apis being added?  Huh?

confused,

greg k-h

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