Re: [PATCH stable-5.4] of: fix linker-section match-table corruption

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Jan 04, 2021 at 10:44:35AM +0100, Johan Hovold wrote:
> commit 5812b32e01c6d86ba7a84110702b46d8a8531fe9 upstream.
> 
> Specify type alignment when declaring linker-section match-table entries
> to prevent gcc from increasing alignment and corrupting the various
> tables with padding (e.g. timers, irqchips, clocks, reserved memory).
> 
> This is specifically needed on x86 where gcc (typically) aligns larger
> objects like struct of_device_id with static extent on 32-byte
> boundaries which at best prevents matching on anything but the first
> entry. Specifying alignment when declaring variables suppresses this
> optimisation.
> 
> Here's a 64-bit example where all entries are corrupt as 16 bytes of
> padding has been inserted before the first entry:
> 
> 	ffffffff8266b4b0 D __clk_of_table
> 	ffffffff8266b4c0 d __of_table_fixed_factor_clk
> 	ffffffff8266b5a0 d __of_table_fixed_clk
> 	ffffffff8266b680 d __clk_of_table_sentinel
> 
> And here's a 32-bit example where the 8-byte-aligned table happens to be
> placed on a 32-byte boundary so that all but the first entry are corrupt
> due to the 28 bytes of padding inserted between entries:
> 
> 	812b3ec0 D __irqchip_of_table
> 	812b3ec0 d __of_table_irqchip1
> 	812b3fa0 d __of_table_irqchip2
> 	812b4080 d __of_table_irqchip3
> 	812b4160 d irqchip_of_match_end
> 
> Verified on x86 using gcc-9.3 and gcc-4.9 (which uses 64-byte
> alignment), and on arm using gcc-7.2.
> 
> Note that there are no in-tree users of these tables on x86 currently
> (even if they are included in the image).
> 
> Fixes: 54196ccbe0ba ("of: consolidate linker section OF match table declarations")
> Fixes: f6e916b82022 ("irqchip: add basic infrastructure")
> Cc: stable <stable@vger.kernel.org>     # 3.9
> Signed-off-by: Johan Hovold <johan@kernel.org>
> Link: https://lore.kernel.org/r/20201123102319.8090-2-johan@kernel.org
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> [ johan: adjust context to 5.4 ]
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
> 
> Greg and Sasha, this one should hopefully apply to all stable trees
> which doesn't have 33def8498fdd ("treewide: Convert macro and uses of
> __section(foo) to __section("foo")").

That worked, thanks!

greg k-h