# Re: \[PATCH v2\] arm64: acpi: fix UBSAN warning

- From: Lorenzo Pieralisi \<hidden\>
- Date: 2020-06-09 18:24:12 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/06/5994876
- Thread: https://ratatoskr.run/stable/2020/06/5986528/t.md

```text
On Mon, Jun 08, 2020 at 01:38:17PM -0700, Nick Desaulniers wrote:
> Will reported a UBSAN warning:
> 
> UBSAN: null-ptr-deref in arch/arm64/kernel/smp.c:596:6
> member access within null pointer of type 'struct acpi_madt_generic_interrupt'
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.7.0-rc6-00124-g96bc42ff0a82 #1
> Call trace:
>  dump_backtrace+0x0/0x384
>  show_stack+0x28/0x38
>  dump_stack+0xec/0x174
>  handle_null_ptr_deref+0x134/0x174
>  __ubsan_handle_type_mismatch_v1+0x84/0xa4
>  acpi_parse_gic_cpu_interface+0x60/0xe8
>  acpi_parse_entries_array+0x288/0x498
>  acpi_table_parse_entries_array+0x178/0x1b4
>  acpi_table_parse_madt+0xa4/0x110
>  acpi_parse_and_init_cpus+0x38/0x100
>  smp_init_cpus+0x74/0x258
>  setup_arch+0x350/0x3ec
>  start_kernel+0x98/0x6f4
> 
> This is from the use of the ACPI_OFFSET in
> arch/arm64/include/asm/acpi.h. Replace its use with offsetof from
> include/linux/stddef.h which should implement the same logic using
> __builtin_offsetof, so that UBSAN wont warn.
> 
> Link: https://lore.kernel.org/lkml/20200521100952.GA5360@willie-the-truck/
> Cc: <redacted>
> Reported-by: Will Deacon <will@kernel.org>
> Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Changes V1 -> V2:
> * Just fix one of the two warnings, specific to arm64.
> * Put warning in commit message.
> 
>  arch/arm64/include/asm/acpi.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Acked-by: Lorenzo Pieralisi <redacted>

> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index b263e239cb59..a45366c3909b 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -12,6 +12,7 @@
>  #include <linux/efi.h>
>  #include <linux/memblock.h>
>  #include <linux/psci.h>
> +#include <linux/stddef.h>
>  
>  #include <asm/cputype.h>
>  #include <asm/io.h>
> @@ -31,14 +32,14 @@
>   * is therefore used to delimit the MADT GICC structure minimum length
>   * appropriately.
>   */
> -#define ACPI_MADT_GICC_MIN_LENGTH   ACPI_OFFSET(  \
> +#define ACPI_MADT_GICC_MIN_LENGTH   offsetof(  \
>  	struct acpi_madt_generic_interrupt, efficiency_class)
>  
>  #define BAD_MADT_GICC_ENTRY(entry, end)					\
>  	(!(entry) || (entry)->header.length < ACPI_MADT_GICC_MIN_LENGTH || \
>  	(unsigned long)(entry) + (entry)->header.length > (end))
>  
> -#define ACPI_MADT_GICC_SPE  (ACPI_OFFSET(struct acpi_madt_generic_interrupt, \
> +#define ACPI_MADT_GICC_SPE  (offsetof(struct acpi_madt_generic_interrupt, \
>  	spe_interrupt) + sizeof(u16))
>  
>  /* Basic configuration for ACPI */
> -- 
> 2.27.0.278.ge193c7cf3a9-goog
> 

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