[SRU][N][PATCH 1/1] x86/platform/uv: Fix UBSAN array-index-out-of-bounds

[Michael Reed]

From: Kyle Meyer <kyle.meyer at hpe.com>

BugLink: https://launchpad.net/bugs/2161004

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:

  https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays

Switch entry in struct uv_systab to a flexible array member to fix UBSAN
array-index-out-of-bounds messages.

sizeof(struct uv_systab) is passed to early_memremap() and ioremap(). The
flexible array member is not accessed until the UV system table size is used to
remap the entire UV system table, so changes to sizeof(struct uv_systab) have no
impact.

Signed-off-by: Kyle Meyer <kyle.meyer at hpe.com>
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Link: https://patch.msgid.link/aTxksN-3otY41WvQ@hpe.com
(cherry picked from commit 21433d3e3ca14d20f9b0c2237b3d3a1355af7907)
Signed-off-by: Michael Reed <Michael.Reed at canonical.com>
---
 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;
 
-- 
2.53.0