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

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Message-Id: <20250709192641.128872-1-kyle.meyer@hpe.com>
Date: Wed,  9 Jul 2025 14:26:41 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: steve.wahl@....com, justin.ernst@....com, kyle.meyer@....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: [PATCH] x86/platform/uv: Fix UBSAN array-index-out-of-bounds

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