kernel/linux.git/arch/s390/include/asm/lowcore.h, branch linux-7.0.y

s390: Add stackprotector support

2025-11-24T10:45:21+00:00

Stackprotector support was previously unavailable on s390 because by default compilers generate code which is not suitable for the kernel: the canary value is accessed via thread local storage, where the address of thread local storage is within access registers 0 and 1. Using those registers also for the kernel would come with a significant performance impact and more complicated kernel entry/exit code, since access registers contents would have to be exchanged on every kernel entry and exit. With the upcoming gcc 16 release new compiler options will become available which allow to generate code suitable for the kernel. [1] Compiler option -mstack-protector-guard=global instructs gcc to generate stackprotector code that refers to a global stackprotector canary value via symbol __stack_chk_guard. Access to this value is guaranteed to occur via larl and lgrl instructions. Furthermore, compiler option -mstack-protector-guard-record generates a section containing all code addresses that reference the canary value. To allow for per task canary values the instructions which load the address of __stack_chk_guard are patched so they access a lowcore field instead: a per task canary value is available within the task_struct of each task, and is written to the per-cpu lowcore location on each context switch. Also add sanity checks and debugging option to be consistent with other kernel code patching mechanisms. Full debugging output can be enabled with the following kernel command line options: debug_stackprotector bootdebug ignore_loglevel earlyprintk dyndbg="file stackprotector.c +p" Example debug output: stackprot: 0000021e402d4eda: c010005a9ae3 -> c01f00070240 where ": -> ". [1] gcc commit 0cd1f03939d5 ("s390: Support global stack protector") Reviewed-by: Sven Schnelle Signed-off-by: Heiko Carstens

s390: Replace ASSEMBLY with ASSEMBLER in non-uapi headers

2025-06-16T14:23:02+00:00

While the GCC and Clang compilers already define __ASSEMBLER__ automatically when compiling assembler code, __ASSEMBLY__ is a macro that only gets defined by the Makefiles in the kernel. This is bad since macros starting with two underscores are names that are reserved by the C language. It can also be very confusing for the developers when switching between userspace and kernelspace coding, or when dealing with uapi headers that rather should use __ASSEMBLER__ instead. So let's now standardize on the __ASSEMBLER__ macro that is provided by the compilers. This is a completely mechanical patch (done with a simple "sed -i" statement), with some manual fixups done later while rebasing the patch. Signed-off-by: Thomas Huth Acked-by: Heiko Carstens Link: https://lore.kernel.org/r/20250611140046.137739-3-thuth@redhat.com Signed-off-by: Alexander Gordeev

s390/lowcore: Remove unused machine_flags

2025-03-31T10:20:39+00:00

The machine_flags member in struct lowcore is not used anymore. Remove it. Reviewed-by: Sven Schnelle Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/lowcore: Use lghi instead llilh to clear register

2025-03-18T16:13:05+00:00

lghi is the fastest way to clear a register. Use that intead of llilh. Suggested-by: Juergen Christ Reviewed-by: Juergen Christ Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/lowcore: Use inline qualifier for get_lowcore() inline assembly

2025-03-18T16:13:04+00:00

Use asm_inline to let the compiler know that the get_lowcore() inline assembly has the smallest possible size. The ALTERNATIVE construct is used to generate a single instruction, however the macro expands to multiple lines. GCC uses the number of lines of an inline assembly to count the number of instructions within an inline assembly, which then has an effect on inlining decisions. In order to avoid incorrect assumptions use asm_inline. The result is that more functions are inlined, which results in a small growth of the kernel image: add/remove: 59/480 grow/shrink: 854/647 up/down: 168780/-162394 (6386) Reviewed-by: Juergen Christ Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/time: Convert MACHINE_HAS_SCC to machine_has_scc()

2025-03-04T16:18:06+00:00

Use static branch(es) to implement and use machine_has_scc() instead of a runtime check via MACHINE_HAS_SCC. This comes with a cleanup of early time initialization: the initial tod_clock_base value is now passed via the bootdata mechanism, instead of using absolute lowcore as transport vehicle from the decompressor to the kernel. Also the early tod clock initialization is moved to the decompressor which allows to use a static branch with machine_has_scc() within the kernel. Reviewed-by: Vasily Gorbik Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/lowcore: Convert relocated lowcore alternative to machine feature

2025-03-04T16:18:05+00:00

Convert the explicit relocated lowcore alternative type to a more generic machine feature. This only reduces the number of alternative types, but has no impact on code generation. Reviewed-by: Vasily Gorbik Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390: Remove gmap pointer from lowcore

2024-10-29T10:49:19+00:00

Remove the gmap pointer from lowcore, since it is not used anymore. Signed-off-by: Claudio Imbrenda Reviewed-by: Steffen Eiden Reviewed-by: Heiko Carstens Link: https://lore.kernel.org/r/20241022120601.167009-9-imbrenda@linux.ibm.com Signed-off-by: Heiko Carstens

s390/entry: Unify save_area_sync and save_area_async

2024-08-29T20:56:34+00:00

In the past two save areas existed because interrupt handlers and system call / program check handlers where entered with interrupts enabled. To prevent a handler from overwriting the save areas from the previous handler, interrupts used the async save area, while system call and program check handler used the sync save area. Since the removal of critical section cleanup from entry.S, handlers are entered with interrupts disabled. When the interrupts are re-enabled, the save area is no longer need. Therefore merge both save areas into one. Reviewed-by: Heiko Carstens Reviewed-by: Alexander Gordeev Signed-off-by: Sven Schnelle Signed-off-by: Vasily Gorbik

s390/entry: Make pgm_check_handler() ready for lowcore relocation

2024-07-23T14:02:32+00:00

In preparation of having lowcore at different address than zero, add the base register to all lowcore accesses in pgm_check_handler(). Reviewed-by: Heiko Carstens Signed-off-by: Sven Schnelle Signed-off-by: Vasily Gorbik