[PATCH] x86/sev: Disable UBSAN on SEV code that may execute very early

[Ard Biesheuvel <ardb@kernel.org>]

Clang 14 and older may emit UBSAN instrumentation into code that is
inlined into functions marked with __no_sanitize_undefined. This may
result in faults when the code is executed very early, which may be the
case for functions annotated as __head. Now that this requirement is
strictly enforced, the build will fail in this case with the following
message

  Absolute reference to symbol '.data' not permitted in .head.text

Work around this by disabling UBSAN instrumentation on all SEV core
code.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/coco/sev/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/coco/sev/Makefile b/arch/x86/coco/sev/Makefile
index 4e375e7305ac..08de37559307 100644
--- a/arch/x86/coco/sev/Makefile
+++ b/arch/x86/coco/sev/Makefile
@@ -13,3 +13,6 @@ KCOV_INSTRUMENT_core.o	:= n
 # With some compiler versions the generated code results in boot hangs, caused
 # by several compilation units. To be safe, disable all instrumentation.
 KCSAN_SANITIZE		:= n
+
+# Clang 14 and older may fail to respect __no_sanitize_undefined when inlining
+UBSAN_SANITIZE		:= n
-- 
2.45.2