The HAVE_CFI_ICALL_NORMALIZE_INTEGERS option has some tricky conditions
when KASAN or GCOV are turned on, as in that case we need some clang and
rustc fixes [1][2] to avoid boot failures. The intent with the current
setup is that you should be able to override the check and turn on the
option if your clang/rustc has the fix. However, this override does not
work in practice. Thus, use the new RUSTC_LLVM_VERSION to correctly
implement the check for whether the fix is available.

Additionally, remove KASAN_HW_TAGS from the list of incompatible
options. The CFI_ICALL_NORMALIZE_INTEGERS option is incompatible with
KASAN because LLVM will emit some constructors when using KASAN that are
assigned incorrect CFI tags. These constructors are emitted due to use
of -fsanitize=kernel-address or -fsanitize=kernel-hwaddress that are
respectively passed when KASAN_GENERIC or KASAN_SW_TAGS are enabled.
However, the KASAN_HW_TAGS option relies on hardware support for MTE
instead and does not pass either flag. (Note also that KASAN_HW_TAGS
does not `select CONSTRUCTORS`.)

Link: https://github.com/llvm/llvm-project/pull/104826 [1]
Link: https://github.com/rust-lang/rust/pull/129373 [2]
Fixes: 4c66f8307ac0 ("cfi: encode cfi normalized integers + kasan/gcov bug in Kconfig")
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 arch/Kconfig | 26 ++++++++++++--------------
 init/Kconfig |  2 +-
 2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8af374ea1adc..00163e4a237c 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -838,7 +838,7 @@ config CFI_CLANG
 config CFI_ICALL_NORMALIZE_INTEGERS
 	bool "Normalize CFI tags for integers"
 	depends on CFI_CLANG
-	depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS
+	depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG
 	help
 	  This option normalizes the CFI tags for integer types so that all
 	  integer types of the same size and signedness receive the same CFI
@@ -851,21 +851,19 @@ config CFI_ICALL_NORMALIZE_INTEGERS
 
 	  This option is necessary for using CFI with Rust. If unsure, say N.
 
-config HAVE_CFI_ICALL_NORMALIZE_INTEGERS
-	def_bool !GCOV_KERNEL && !KASAN
-	depends on CFI_CLANG
+config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG
+	def_bool y
 	depends on $(cc-option,-fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers)
-	help
-	  Is CFI_ICALL_NORMALIZE_INTEGERS supported with the set of compilers
-	  currently in use?
+	# With GCOV/KASAN we need this fix: https://github.com/llvm/llvm-project/pull/104826
+	depends on CLANG_VERSION >= 190000 || (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS)
 
-	  This option defaults to false if GCOV or KASAN is enabled, as there is
-	  an LLVM bug that makes normalized integers tags incompatible with
-	  KASAN and GCOV. Kconfig currently does not have the infrastructure to
-	  detect whether your rustc compiler contains the fix for this bug, so
-	  it is assumed that it doesn't. If your compiler has the fix, you can
-	  explicitly enable this option in your config file. The Kconfig logic
-	  needed to detect this will be added in a future kernel release.
+config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC
+	def_bool y
+	depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG
+	depends on RUSTC_VERSION >= 107900
+	# With GCOV/KASAN we need this fix: https://github.com/rust-lang/rust/pull/129373
+	depends on (RUSTC_LLVM_VERSION >= 190000 && RUSTC_VERSION >= 108200) || \
+		(!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS)
 
 config CFI_PERMISSIVE
 	bool "Use CFI in permissive mode"
diff --git a/init/Kconfig b/init/Kconfig
index 98cf859d58c2..c521e1421ad4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1950,7 +1950,7 @@ config RUST
 	depends on !GCC_PLUGIN_RANDSTRUCT
 	depends on !RANDSTRUCT
 	depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
-	depends on !CFI_CLANG || RUSTC_VERSION >= 107900 && HAVE_CFI_ICALL_NORMALIZE_INTEGERS
+	depends on !CFI_CLANG || HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC
 	select CFI_ICALL_NORMALIZE_INTEGERS if CFI_CLANG
 	depends on !CALL_PADDING || RUSTC_VERSION >= 108100
 	depends on !KASAN_SW_TAGS

-- 
2.47.0.rc0.187.ge670bccf7e-goog

On Thu, Oct 10, 2024 at 09:38:27AM +0000, Alice Ryhl wrote:
> The HAVE_CFI_ICALL_NORMALIZE_INTEGERS option has some tricky conditions
> when KASAN or GCOV are turned on, as in that case we need some clang and
> rustc fixes [1][2] to avoid boot failures. The intent with the current
> setup is that you should be able to override the check and turn on the
> option if your clang/rustc has the fix. However, this override does not
> work in practice. Thus, use the new RUSTC_LLVM_VERSION to correctly
> implement the check for whether the fix is available.
> 
> Additionally, remove KASAN_HW_TAGS from the list of incompatible
> options. The CFI_ICALL_NORMALIZE_INTEGERS option is incompatible with
> KASAN because LLVM will emit some constructors when using KASAN that are
> assigned incorrect CFI tags. These constructors are emitted due to use
> of -fsanitize=kernel-address or -fsanitize=kernel-hwaddress that are
> respectively passed when KASAN_GENERIC or KASAN_SW_TAGS are enabled.
> However, the KASAN_HW_TAGS option relies on hardware support for MTE
> instead and does not pass either flag. (Note also that KASAN_HW_TAGS
> does not `select CONSTRUCTORS`.)
> 
> Link: https://github.com/llvm/llvm-project/pull/104826 [1]
> Link: https://github.com/rust-lang/rust/pull/129373 [2]
> Fixes: 4c66f8307ac0 ("cfi: encode cfi normalized integers + kasan/gcov bug in Kconfig")
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

This looks correct to me. Checking the LLVM version is definitely a
better option. Thanks!

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>

Sami