linux-kernel - Re: [PATCH] x86/platform/uv: Fix UBSAN array-index-out-of-bounds

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Message-ID: <aKddpjJnmcuhrH6T@hpe.com>
Date: Thu, 21 Aug 2025 12:55:50 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: steve.wahl@....com, justin.ernst@....com, dimitri.sivanich@....com,
        russ.anderson@....com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/platform/uv: Fix UBSAN array-index-out-of-bounds

On Wed, Jul 09, 2025 at 02:26:41PM -0500, Kyle Meyer wrote:
> When UBSAN is enabled, multiple array-index-out-of-bounds messages are
> written to the ring buffer:
> 
> [    0.000000] [     T0] UBSAN: array-index-out-of-bounds in arch/x86/kernel/apic/x2apic_uv_x.c:276:23
> [    0.000000] [     T0] index 1 is out of range for type '<unknown> [1]'
> ...
> [    0.000000] [     T0] UBSAN: array-index-out-of-bounds in arch/x86/kernel/apic/x2apic_uv_x.c:277:32
> [    0.000000] [     T0] index 1 is out of range for type '<unknown> [1]'
> ...
> [    0.000000] [     T0] UBSAN: array-index-out-of-bounds in arch/x86/kernel/apic/x2apic_uv_x.c:282:16
> [    0.000000] [     T0] index 1 is out of range for type '<unknown> [1]'
> ...
> [    0.515850] [     T1] UBSAN: array-index-out-of-bounds in arch/x86/kernel/apic/x2apic_uv_x.c:1344:23
> [    0.519851] [     T1] index 1 is out of range for type '<unknown> [1]'
> ...
> [    0.603850] [     T1] UBSAN: array-index-out-of-bounds in arch/x86/kernel/apic/x2apic_uv_x.c:1345:32
> [    0.607850] [     T1] index 1 is out of range for type '<unknown> [1]'
> ...
> [    0.691850] [     T1] UBSAN: array-index-out-of-bounds in arch/x86/kernel/apic/x2apic_uv_x.c:1353:20
> [    0.695850] [     T1] index 1 is out of range for type '<unknown> [1]'
> 
> One-element arrays have been deprecated [1]. Switch entry
> in struct uv_systab to a flexible array member to fix UBSAN
> array-index-out-of-bounds messages.
> 
> [1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Signed-off-by: Kyle Meyer <kyle.meyer@....com>
> ---
> 
> sizeof(struct uv_systab) is passed to early_memremap() and ioremap(). The
> flexible array member is not referenced until the entire UV system table is
> remapped, so this changes to sizeof(struct uv_systab) would have no impact
> anyway.
> 
>  arch/x86/include/asm/uv/bios.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/uv/bios.h b/arch/x86/include/asm/uv/bios.h
> index 6989b824fd32..d0b62e255290 100644
> --- a/arch/x86/include/asm/uv/bios.h
> +++ b/arch/x86/include/asm/uv/bios.h
> @@ -122,7 +122,7 @@ struct uv_systab {
>  	struct {
>  		u32 type:8;	/* type of entry */
>  		u32 offset:24;	/* byte offset from struct start to entry */
> -	} entry[1];		/* additional entries follow */
> +	} entry[];		/* additional entries follow */
>  };
>  extern struct uv_systab *uv_systab;
>  
> -- 
> 2.50.0
> 

Just a friendly ping.

Thanks,
Kyle Meyer