kernel/arch/s390/boot/startup.c, branch linux-rolling-stable

s390: Add stackprotector support

2025-11-24T10:45:21Z

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/boot: Add common boot_panic() code

2025-08-28T14:52:54Z

Introduce a common boot_panic() helper macro, and use it to get rid of three more or less identical implementations. Signed-off-by: Heiko Carstens Reviewed-by: Alexander Gordeev Signed-off-by: Alexander Gordeev

s390/boot: Fix startup debugging log

2025-08-06T15:18:27Z

Fix 'kernel image' end address for kaslr case. Fixes: ec6f9f7e5bbf ("s390/boot: Add startup debugging support") Reviewed-by: Alexander Gordeev Signed-off-by: Mikhail Zaslonko Signed-off-by: Heiko Carstens Signed-off-by: Alexander Gordeev

s390/boot: Introduce jump_to_kernel() function

2025-07-10T12:42:10Z

Introduce a global function that jumps from the decompressor to the decompressed kernel. Put its address into svc_old_psw, from where GDB can take it without loading decompressor symbols. It should be available throughout the entire decompressor execution, because it's placed there statically, and nothing in the decompressor uses the SVC instruction. Acked-by: Heiko Carstens Signed-off-by: Ilya Leoshkevich Tested-by: Alexander Gordeev Link: https://lore.kernel.org/r/20250625154220.75300-2-iii@linux.ibm.com Signed-off-by: Alexander Gordeev

watchdog: diag288_wdt: Implement module autoload

2025-04-16T07:26:49Z

The s390 specific diag288_wdt watchdog driver makes use of the virtual watchdog timer, which is available in most machine configurations. If executing the diagnose instruction with subcode 0x288 results in an exception the watchdog timer is not available, otherwise it is available. In order to allow module autoload of the diag288_wdt module, move the detection of the virtual watchdog timer to early boot code, and provide its availability as a cpu feature. This allows to make use of module_cpu_feature_match() to automatically load the module iff the virtual watchdog timer is available. Suggested-by: Marc Hartmayer Tested-by: Mete Durlu Acked-by: Guenter Roeck Link: https://lore.kernel.org/r/20250410095036.1525057-1-hca@linux.ibm.com Signed-off-by: Heiko Carstens

s390: Use inline qualifier for all EX_TABLE and ALTERNATIVE inline assemblies

2025-03-18T16:13:51Z

Use asm_inline for all inline assemblies which make use of the EX_TABLE or ALTERNATIVE macros. These macros expand to many lines and the compiler assumes the number of lines within an inline assembly is the same as the number of instructions within an inline assembly. This has an effect on inlining and loop unrolling decisions. In order to avoid incorrect assumptions use asm_inline, which tells the compiler that an inline assembly has the smallest possible size. In order to avoid confusion when asm_inline should be used or not, since a couple of inline assemblies are quite large: the rule is to always use asm_inline whenever the EX_TABLE or ALTERNATIVE macro is used. In specific cases there may be reasons to not follow this guideline, but that should be documented with the corresponding code. Using the inline qualifier everywhere has only a small effect on the kernel image size: add/remove: 0/10 grow/shrink: 19/8 up/down: 1492/-1858 (-366) The only location where this seems to matter is load_unaligned_zeropad() from word-at-a-time.h where the compiler inlines more functions within the dcache code, which is indeed code where performance matters. Suggested-by: Juergen Christ Reviewed-by: Juergen Christ Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/boot: Convert detect_diag9c() to extable

2025-03-04T16:34:03Z

Shorten detect_diag9c() and use regular EX_TABLE program check handling. Acked-by: Alexander Gordeev Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/boot: Convert cmma_test_essa() to extable

2025-03-04T16:33:40Z

Shorten cmma_test_essa() and use regular EX_TABLE program check handling. Acked-by: Alexander Gordeev Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/vx: Convert cpu_has_vx() to cpu feature function

2025-03-04T16:18:07Z

Instead of having a private cpu_has_vx() implementation use the new common cpu feature method. Move the facility detection to the decompressor so it matches all other cpu features. Reviewed-by: Vasily Gorbik Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390: Convert MACHINE_IS_[LPAR|VM|KVM], etc, machine_is_[lpar|vm|kvm]()

2025-03-04T16:18:07Z

Move machine type detection to the decompressor and use static branches to implement and use machine_is_[lpar|vm|kvm]() instead of a runtime check via MACHINE_IS_[LPAR|VM|KVM]. Reviewed-by: Vasily Gorbik Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik