[SRU][N][PATCH 0/1] Fix UBSAN array-index-out-of-bounds

[Michael Reed]

From: Michael Reed <Michael.Reed at canonical.com>

SRU Justification

[ Impact ]

When UBSAN is enabled, multiple array-index-out-of-bounds messages are
printed:

  [ 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:

[ Fix ]

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=21433d3e3ca14d20f9b0c2237b3d3a1355af7907

[ Test Plan ]

 Installed 24.04.
 apt upgrade to install the latest kernel (6.8.0-136).
 Reboot with 6.8.0-136.
 Confirmed UBSAN warning messages (same as bug description).

 Installed lp_2161004_ubsan_array_index deb packages.
 Reboot with new kernel
 Confirmed no UBSAM warning messages.

Kernel without the fix (July 1 build date):
[ 0.000000] Linux version 6.8.0-136-generic (buildd at lcy02-amd64-041) (x86_64-linux-gnu-gcc-13 (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0, GNU ld (GNU Binutils for Ubuntu) 2.42) #136-Ubuntu SMP PREEMPT_DYNAMIC Wed Jul 1 21:53:05 UTC 2026 (Ubuntu 6.8.0-136.136-generic 6.8.12)

Kernel with the fix (July 16 build date):
[ 0.000000] Linux version 6.8.0-136-generic (root at buildnoble) (x86_64-linux-gnu-gcc-13 (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0, GNU ld (GNU Binutils for Ubuntu) 2.42) #136 SMP PREEMPT_DYNAMIC Thu Jul 16 20:05:25 UTC 2026 (Ubuntu 6.8.0-136.136-generic 6.8.12)

[ Where problems could occur ]

The regression risk is low

[ Other Info ]

https://code.launchpad.net/~mreed8855/ubuntu/+source/linux/+git/noble/+ref/ubsan_array_index 
 
Kyle Meyer (1):
  x86/platform/uv: Fix UBSAN array-index-out-of-bounds

 arch/x86/include/asm/uv/bios.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.53.0