linux-hardening - Re: [PATCH] kunit/usercopy: Disable u64 test on 32-bit SPARC

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Message-ID: <202504161052.4011756D7@keescook>
Date: Wed, 16 Apr 2025 10:53:14 -0700
From: Kees Cook <kees@...nel.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Gow <davidgow@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andreas Larsson <andreas@...sler.com>, sparclinux@...r.kernel.org
Subject: Re: [PATCH] kunit/usercopy: Disable u64 test on 32-bit SPARC

On Wed, Apr 16, 2025 at 02:44:19PM +0200, Thomas Weißschuh wrote:
> usercopy of 64 bit values does not work on 32-bit SPARC:
> 
>     # usercopy_test_valid: EXPECTATION FAILED at lib/tests/usercopy_kunit.c:209
>     Expected val_u64 == 0x5a5b5c5d6a6b6c6d, but
>         val_u64 == 1515936861 (0x5a5b5c5d)
>         0x5a5b5c5d6a6b6c6d == 6510899242581322861 (0x5a5b5c5d6a6b6c6d)
> 
> Disable the test.
> 
> Fixes: 4c5d7bc63775 ("usercopy: Add tests for all get_user() sizes")
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> ---
> To be honest I think sparc32 wants to support usercopy of 64 bit values.
> But it does seem to be broken.
> 
> (+Cc SPARC maintainers)

I wonder if these archs need to explicitly fail to build if they trigger
a 64-bit wide put_user/get_user call? It seems weird to me that it
should be possible at all to provide access to the function if we know
it's going to 100% fail.

-Kees

> ---
>  lib/tests/usercopy_kunit.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/tests/usercopy_kunit.c b/lib/tests/usercopy_kunit.c
> index 77fa00a13df775074a19772bfbc9120ef33634bb..80f8abe10968c1d91c61006f1eaa63858c633872 100644
> --- a/lib/tests/usercopy_kunit.c
> +++ b/lib/tests/usercopy_kunit.c
> @@ -27,6 +27,7 @@
>  			    !defined(CONFIG_MICROBLAZE) &&	\
>  			    !defined(CONFIG_NIOS2) &&		\
>  			    !defined(CONFIG_PPC32) &&		\
> +			    !defined(CONFIG_SPARC32) &&		\
>  			    !defined(CONFIG_SUPERH))
>  # define TEST_U64
>  #endif
> 
> ---
> base-commit: 1a1d569a75f3ab2923cb62daf356d102e4df2b86
> change-id: 20250416-kunit-sparc-usercopy-c36de3ca4ef8
> 
> Best regards,
> -- 
> Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> 

-- 
Kees Cook