[PATCH 1/2] kernel: add missing UBSAN config symbols

[Hauke Mehrtens]

On 11/3/21 7:08 PM, Stijn Tintel wrote:
> Enabling KERNEL_UBSAN exposes several missing symbols. Add new kernel
> build options for UBSAN_BOUNDS and UBSAN_TRAP, disable CONFIG_TEST_UBSAN
> in the generic kernel configs and enable CONFIG_UBSAN_MISC in generic
> 5.10 config. The latter symbol was removed in later kernels, so just set
> it to the default value in 5.10 instead of adding a build option for it.
> 
> Fixes build failures with KERNEL_UBSAN enabled.

Does your system still boot with CONFIG_UBSAN_MISC set?
I haven't tried this myself and used this only on an older kernel 
before, but this commit message which removes it does not sound good:
https://git.kernel.org/linus/c637693b20da8706b7f48d96882c9c80ae935151

I would prefer to deactivate CONFIG_UBSAN_MISC.

Hauke

> 
> Signed-off-by: Stijn Tintel <stijn at linux-ipv6.be>
> ---
>   config/Config-kernel.in          | 23 +++++++++++++++++++++++
>   target/linux/generic/config-5.10 |  2 ++
>   target/linux/generic/config-5.4  |  1 +
>   3 files changed, 26 insertions(+)
> 
> diff --git a/config/Config-kernel.in b/config/Config-kernel.in
> index dc249a6031..6758d278e7 100644
> --- a/config/Config-kernel.in
> +++ b/config/Config-kernel.in
> @@ -114,6 +114,16 @@ config KERNEL_UBSAN_ALIGNMENT
>   	  Enabling this option on architectures that support unaligned
>   	  accesses may produce a lot of false positives.
>   
> +config KERNEL_UBSAN_BOUNDS
> +	bool "Perform array index bounds checking"
> +	depends on KERNEL_UBSAN
> +	help
> +	  This option enables detection of directly indexed out of bounds array
> +	  accesses, where the array size is known at compile time. Note that
> +	  this does not protect array overflows via bad calls to the
> +	  {str,mem}*cpy() family of functions (that is addressed by
> +	  FORTIFY_SOURCE).
> +
>   config KERNEL_UBSAN_NULL
>   	bool "Enable checking of null pointers"
>   	depends on KERNEL_UBSAN
> @@ -121,6 +131,19 @@ config KERNEL_UBSAN_NULL
>   	  This option enables detection of memory accesses via a
>   	  null pointer.
>   
> +config KERNEL_UBSAN_TRAP
> +	bool "On Sanitizer warnings, abort the running kernel code"
> +	depends on KERNEL_UBSAN
> +	help
> +	  Building kernels with Sanitizer features enabled tends to grow the
> +	  kernel size by around 5%, due to adding all the debugging text on
> +	  failure paths. To avoid this, Sanitizer instrumentation can just
> +	  issue a trap. This reduces the kernel size overhead but turns all
> +	  warnings (including potentially harmless conditions) into full
> +	  exceptions that abort the running kernel code (regardless of context,
> +	  locks held, etc), which may destabilize the system. For some system
> +	  builders this is an acceptable trade-off.
> +
>   config KERNEL_KASAN
>   	bool "Compile the kernel with KASan: runtime memory debugger"
>   	select KERNEL_SLUB_DEBUG
> diff --git a/target/linux/generic/config-5.10 b/target/linux/generic/config-5.10
> index 7b952e8ca8..83004d0879 100644
> --- a/target/linux/generic/config-5.10
> +++ b/target/linux/generic/config-5.10
> @@ -6082,6 +6082,7 @@ CONFIG_TCP_CONG_CUBIC=y
>   # CONFIG_TEST_STRING_HELPERS is not set
>   # CONFIG_TEST_STRSCPY is not set
>   # CONFIG_TEST_SYSCTL is not set
> +# CONFIG_TEST_UBSAN is not set
>   # CONFIG_TEST_UDELAY is not set
>   # CONFIG_TEST_USER_COPY is not set
>   # CONFIG_TEST_UUID is not set
> @@ -6348,6 +6349,7 @@ CONFIG_UBIFS_FS_ZLIB=y
>   CONFIG_UBIFS_FS_ZSTD=y
>   # CONFIG_UBSAN is not set
>   CONFIG_UBSAN_ALIGNMENT=y
> +CONFIG_UBSAN_MISC=y
>   # CONFIG_UCB1400_CORE is not set
>   # CONFIG_UCSI is not set
>   # CONFIG_UDF_FS is not set
> diff --git a/target/linux/generic/config-5.4 b/target/linux/generic/config-5.4
> index c44e9cf40b..bf2b462529 100644
> --- a/target/linux/generic/config-5.4
> +++ b/target/linux/generic/config-5.4
> @@ -5631,6 +5631,7 @@ CONFIG_TCP_CONG_CUBIC=y
>   # CONFIG_TEST_STRING_HELPERS is not set
>   # CONFIG_TEST_STRSCPY is not set
>   # CONFIG_TEST_SYSCTL is not set
> +# CONFIG_TEST_UBSAN is not set
>   # CONFIG_TEST_UDELAY is not set
>   # CONFIG_TEST_USER_COPY is not set
>   # CONFIG_TEST_UUID is not set
>