Re: Patch "ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18" has been added to the 6.12-stable tree

[Nathan Chancellor <nathan@kernel.org>]

On Sun, Mar 08, 2026 at 12:41:28PM -0400, Sasha Levin wrote:
> This is a note to let you know that I've just added the patch titled
> 
>     ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18
> 
> to the 6.12-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      acpi-apei-ghes-disable-kasan-instrumentation-when-co.patch
> and it can be found in the queue-6.12 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
> 
> 
> 
> commit ccd3cab8095d5c53eaf8a6598ff339ffaad6a696
> Author: Nathan Chancellor <nathan@kernel.org>
> Date:   Wed Jan 14 16:27:11 2026 -0700
> 
>     ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18
>     
>     [ Upstream commit b584bfbd7ec417f257f651cc00a90c66e31dfbf1 ]
>     
>     After a recent innocuous change to drivers/acpi/apei/ghes.c, building
>     ARCH=arm64 allmodconfig with clang-17 or older (which has both
>     CONFIG_KASAN=y and CONFIG_WERROR=y) fails with:
>     
>       drivers/acpi/apei/ghes.c:902:13: error: stack frame size (2768) exceeds limit (2048) in 'ghes_do_proc' [-Werror,-Wframe-larger-than]
>         902 | static void ghes_do_proc(struct ghes *ghes,
>             |             ^
>     
>     A KASAN pass that removes unneeded stack instrumentation, enabled by
>     default in clang-18 [1], drastically improves stack usage in this case.
>     
>     To avoid the warning in the common allmodconfig case when it can break
>     the build, disable KASAN for ghes.o when compile testing with clang-17
>     and older. Disabling KASAN outright may hide legitimate runtime issues,
>     so live with the warning in that case; the user can either increase the
>     frame warning limit or disable -Werror, which they should probably do
>     when debugging with KASAN anyways.
>     
>     Closes: https://github.com/ClangBuiltLinux/linux/issues/2148
>     Link: https://github.com/llvm/llvm-project/commit/51fbab134560ece663517bf1e8c2a30300d08f1a [1]
>     Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>     Cc: All applicable <stable@vger.kernel.org>
>     Link: https://patch.msgid.link/20260114-ghes-avoid-wflt-clang-older-than-18-v1-1-9c8248bfe4f4@kernel.org
>     Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>     Signed-off-by: Sasha Levin <sashal@kernel.org>
> 
> diff --git a/drivers/acpi/apei/Makefile b/drivers/acpi/apei/Makefile
> index 5db61dfb46915..1a0b85923cd42 100644
> --- a/drivers/acpi/apei/Makefile
> +++ b/drivers/acpi/apei/Makefile
> @@ -1,6 +1,10 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_ACPI_APEI)		+= apei.o
>  obj-$(CONFIG_ACPI_APEI_GHES)	+= ghes.o
> +# clang versions prior to 18 may blow out the stack with KASAN
> +ifeq ($(CONFIG_COMPILE_TEST)_$(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_y_)
> +KASAN_SANITIZE_ghes.o := n
> +endif
>  obj-$(CONFIG_ACPI_APEI_PCIEAER)	+= ghes_helpers.o
>  obj-$(CONFIG_ACPI_APEI_EINJ)	+= einj.o
>  einj-y				:= einj-core.o

The backports you have taken to make this apply cleanly to 6.12

  20260308164114.18890-1-sashal@kernel.org
  20260308164118.18945-1-sashal@kernel.org
  20260308164121.19006-1-sashal@kernel.org
  20260308164125.19064-1-sashal@kernel.org

are excessive in my opinion. I think you should just address the
conflict... There is absolutely no dependency on those changes so
"Stable-dep-of" is a bit misleading.

diff --git a/drivers/acpi/apei/Makefile b/drivers/acpi/apei/Makefile
index 2c474e6477e1..346cdf0a0ef9 100644
--- a/drivers/acpi/apei/Makefile
+++ b/drivers/acpi/apei/Makefile
@@ -1,6 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_ACPI_APEI)		+= apei.o
 obj-$(CONFIG_ACPI_APEI_GHES)	+= ghes.o
+# clang versions prior to 18 may blow out the stack with KASAN
+ifeq ($(CONFIG_COMPILE_TEST)_$(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_y_)
+KASAN_SANITIZE_ghes.o := n
+endif
 obj-$(CONFIG_ACPI_APEI_EINJ)	+= einj.o
 einj-y				:= einj-core.o
 einj-$(CONFIG_ACPI_APEI_EINJ_CXL) += einj-cxl.o