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| author |   Vasily Gorbik <gor@linux.ibm.com> | 2022-03-06 20:56:07 +0100 |
|---|---|---|
| committer | Vasily Gorbik <gor@linux.ibm.com> | 2022-03-10 15:58:17 +0100 |
| commit | 1d2ad084800edad81cdc955304272742b10721c7 (patch) | |
| tree | dc6e27260422f6792ffb40a3e7b4d06c7fcf0720 /arch/s390/Kconfig | |
| parent | s390/nospec: generate single register thunks if possible (diff) | |
| download | linux-dev-1d2ad084800edad81cdc955304272742b10721c7.tar.xz linux-dev-1d2ad084800edad81cdc955304272742b10721c7.zip | |
s390/nospec: add an option to use thunk-extern
Currently with -mindirect-branch=thunk and -mfunction-return=thunk compiler
options expoline thunks are put into individual COMDAT group sections. s390
is the only architecture which has group sections and it has implications
for kpatch and objtool tools support.
Using -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern
is an alternative, which comes with a need to generate all required
expoline thunks manually. Unfortunately modules area is too far away from
the kernel image, and expolines from the kernel image cannon be used.
But since all new distributions (except Debian) build kernels for machine
generations newer than z10, where "exrl" instruction is available, that
leaves only 16 expolines thunks possible.
Provide an option to build the kernel with
-mindirect-branch=thunk-extern and -mfunction-return=thunk-extern for
z10 or newer. This also requires to postlink expoline thunks into all
modules explicitly. Currently modules already contain most expolines
anyhow.
Unfortunately -mindirect-branch=thunk-extern and
-mfunction-return=thunk-extern options support is broken in gcc <= 11.2.
Additional compile test is required to verify proper gcc support.
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Co-developed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390/Kconfig')
| -rw-r--r-- | arch/s390/Kconfig | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig index a492376d6e3f..115b8cddefee 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -585,6 +585,7 @@ config KERNEL_NOBP config EXPOLINE def_bool n + depends on $(cc-option,-mindirect-branch=thunk) prompt "Avoid speculative indirect branches in the kernel" help Compile the kernel with the expoline compiler options to guard @@ -595,6 +596,20 @@ config EXPOLINE If unsure, say N. +config EXPOLINE_EXTERN + def_bool n + depends on EXPOLINE + depends on HAVE_MARCH_Z10_FEATURES + depends on CC_IS_GCC && GCC_VERSION >= 110200 + depends on $(success,$(srctree)/arch/s390/tools/gcc-thunk-extern.sh $(CC)) + prompt "Generate expolines as extern functions." + help + This option is required for some tooling like kpatch. The kernel is + compiled with -mindirect-branch=thunk-extern and requires a newer + compiler. + + If unsure, say N. + choice prompt "Expoline default" depends on EXPOLINE |