kernel/arch/s390/boot/vmlinux.lds.S, branch linux-rolling-stable

s390/boot/vmlinux.lds.S: Ensure bzImage ends with SecureBoot trailer

2026-01-30T09:32:25Z

commit ddc6cbef3ef10359b5640b4ee810a520edc73586 upstream. Since commit 3e86e4d74c04 ("kbuild: keep .modinfo section in vmlinux.unstripped") the .modinfo section which has SHF_ALLOC ends up in bzImage after the SecureBoot trailer. This breaks SecureBoot because the bootloader can no longer find the SecureBoot trailer with kernel's signature at the expected location in bzImage. To fix the bug, move discarded sections before the ELF_DETAILS macro and discard the .modinfo section which is not needed by the decompressor. Fixes: 3e86e4d74c04 ("kbuild: keep .modinfo section in vmlinux.unstripped") Cc: stable@vger.kernel.org Suggested-by: Vasily Gorbik Reviewed-by: Vasily Gorbik Tested-by: Vasily Gorbik Signed-off-by: Alexander Egorenkov Signed-off-by: Heiko Carstens Signed-off-by: Greg Kroah-Hartman

s390/boot: Add exception table support

2025-03-04T16:25:22Z

The early boot code contains various open-coded inline assemblies with exception handling. In order to handle possible exceptions each of them changes the program check new psw, and restores it. In order to simplify the various inline assemblies add simple exception table support: the program check handler is called with a fully populated pt_regs on the stack and may change the psw and register members. When the program check handler returns the psw and registers from pt_regs will be used to continue execution. The program check handler searches the exception table for an entry which matches the address of the program check. If such an entry is found the psw address within pt_regs on the stack is replaced with a fixup address, and execution continues at the new address. If no entry is found the psw is changed to a disabled wait psw and execution stops. Before entering the C part of the program check handler the address of the program check new psw is replaced to a minimalistic handler. This is supposed to help against program check loops. If an exception happens while in program check processing the register contents of the original exception are restored and a disabled wait psw is loaded. Acked-by: Alexander Gordeev Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/boot: Fix KASLR base offset off by __START_KERNEL bytes

2024-08-22T17:24:13Z

Symbol offsets to the KASLR base do not match symbol address in the vmlinux image. That is the result of setting the KASLR base to the beginning of .text section as result of an optimization. Revert that optimization and allocate virtual memory for the whole kernel image including __START_KERNEL bytes as per the linker script. That allows keeping the semantics of the KASLR base offset in sync with other architectures. Rename __START_KERNEL to TEXT_OFFSET, since it represents the offset of the .text section within the kernel image, rather than a virtual address. Still skip mapping TEXT_OFFSET bytes to save memory on pgtables and provoke exceptions in case an attempt to access this area is made, as no kernel symbol may reside there. In case CONFIG_KASAN is enabled the location counter might exceed the value of TEXT_OFFSET, while the decompressor linker script forcefully resets it to TEXT_OFFSET, which leads to a sections overlap link failure. Use MAX() expression to avoid that. Reported-by: Omar Sandoval Closes: https://lore.kernel.org/linux-s390/ZnS8dycxhtXBZVky@telecaster.dhcp.thefacebook.com/ Fixes: 56b1069c40c7 ("s390/boot: Rework deployment of the kernel image") Signed-off-by: Alexander Gordeev Acked-by: Vasily Gorbik Signed-off-by: Vasily Gorbik

s390/mm: Restore mapping of kernel image using large pages

2024-06-11T14:20:40Z

Since physical and virtual kernel address spaces are uncoupled the kernel image is not mapped using large segment pages anymore, which is a regression. Put the kernel image at the same large segment page offset in physical memory as in virtual memory. Such approach preserves the existing number of bits of entropy used for randomization of the kernel location in virtual memory when KASLR is on. As result, the kernel is mapped using large segment pages. Fixes: c98d2ecae08f ("s390/mm: Uncouple physical vs virtual address spaces") Reported-by: Heiko Carstens Reviewed-by: Heiko Carstens Signed-off-by: Alexander Gordeev Signed-off-by: Vasily Gorbik

s390: Compile kernel with -fPIC and link with -no-pie

2024-04-29T15:33:30Z

When the kernel is built with CONFIG_PIE_BUILD option enabled it uses dynamic symbols, for which the linker does not allow more than 64K number of entries. This can break features like kpatch. Hence, whenever possible the kernel is built with CONFIG_PIE_BUILD option disabled. For that support of unaligned symbols generated by linker scripts in the compiler is necessary. However, older compilers might lack such support. In that case the build process resorts to CONFIG_PIE_BUILD option-enabled build. Compile object files with -fPIC option and then link the kernel binary with -no-pie linker option. As result, the dynamic symbols are not generated and not only kpatch feature succeeds, but also the whole CONFIG_PIE_BUILD option-enabled code could be dropped. [ agordeev: Reworded the commit message ] Suggested-by: Ulrich Weigand Signed-off-by: Sumanth Korikkar Reviewed-by: Alexander Gordeev Signed-off-by: Alexander Gordeev

s390/boot: Do not rescue .vmlinux.relocs section

2024-04-17T11:38:02Z

The .vmlinux.relocs section is moved in front of the compressed kernel. The interim section rescue step is avoided as result. Suggested-by: Sumanth Korikkar Signed-off-by: Alexander Gordeev

s390/boot: Rework deployment of the kernel image

2024-04-17T11:38:02Z

Rework deployment of kernel image for both compressed and uncompressed variants as defined by CONFIG_KERNEL_UNCOMPRESSED kernel configuration variable. In case CONFIG_KERNEL_UNCOMPRESSED is disabled avoid uncompressing the kernel to a temporary buffer and copying it to the target address. Instead, uncompress it directly to the target destination. In case CONFIG_KERNEL_UNCOMPRESSED is enabled avoid moving the kernel to default 0x100000 location when KASLR is disabled or failed. Instead, use the uncompressed kernel image directly. In case KASLR is disabled or failed .amode31 section location in memory is not randomized and precedes the kernel image. In case CONFIG_KERNEL_UNCOMPRESSED is disabled that location overlaps the area used by the decompression algorithm. That is fine, since that area is not used after the decompression finished and the size of .amode31 section is not expected to exceed BOOT_HEAP_SIZE ever. There is no decompression in case CONFIG_KERNEL_UNCOMPRESSED is enabled. Therefore, rename decompress_kernel() to deploy_kernel(), which better describes both uncompressed and compressed cases. Introduce AMODE31_SIZE macro to avoid immediate value of 0x3000 (the size of .amode31 section) in the decompressor linker script. Modify the vmlinux linker script to force the size of .amode31 section to AMODE31_SIZE (the value of (_eamode31 - _samode31) could otherwise differ as result of compiler options used). Introduce __START_KERNEL macro that defines the kernel ELF image entry point and set it to the currrent value of 0x100000. Signed-off-by: Alexander Gordeev

s390: vmlinux.lds.S: fix .got.plt assertion

2024-02-25T17:01:09Z

Naresh reported this build error on linux-next: s390x-linux-gnu-ld: Unexpected GOT/PLT entries detected! make[3]: *** [/builds/linux/arch/s390/boot/Makefile:87: arch/s390/boot/vmlinux.syms] Error 1 make[3]: Target 'arch/s390/boot/bzImage' not remade because of errors. The reason for the build error is an incorrect/incomplete assertion which checks the size of the .got.plt section. Similar to x86 the size is either zero or 24 bytes (three entries). See commit 262b5cae67a6 ("x86/boot/compressed: Move .got.plt entries out of the .got section") for more details. The three reserved/additional entries for s390 are described in chapter 3.2.2 of the s390x ABI [1] (thanks to Andreas Krebbel for pointing this out!). [1] https://github.com/IBM/s390x-abi/releases/download/v1.6.1/lzsabi_s390x.pdf Reported-by: Naresh Kamboju Reported-by: Linux Kernel Functional Testing Closes: https://lore.kernel.org/all/CA+G9fYvWp8TY-fMEvc3UhoVtoR_eM5VsfHj3+n+kexcfJJ+Cvw@mail.gmail.com Fixes: 30226853d6ec ("s390: vmlinux.lds.S: explicitly handle '.got' and '.plt' sections") Signed-off-by: Heiko Carstens

s390: compile relocatable kernel without -fPIE

2024-02-20T13:37:33Z

On s390, currently kernel uses the '-fPIE' compiler flag for compiling vmlinux. This has a few problems: - It uses dynamic symbols (.dynsym), for which the linker refuses to allow more than 64k sections. This can break features which use '-ffunction-sections' and '-fdata-sections', including kpatch-build [1] and Function Granular KASLR. - It unnecessarily uses GOT relocations, adding an extra layer of indirection for many memory accesses. Instead of using '-fPIE', resolve all the relocations at link time and then manually adjust any absolute relocations (R_390_64) during boot. This is done by first telling the linker to preserve all relocations during the vmlinux link. (Note this is harmless: they are later stripped in the vmlinux.bin link.) Then use the 'relocs' tool to find all absolute relocations (R_390_64) which apply to allocatable sections. The offsets of those relocations are saved in a special section which is then used to adjust the relocations during boot. (Note: For some reason, Clang occasionally creates a GOT reference, even without '-fPIE'. So Clang-compiled kernels have a GOT, which needs to be adjusted.) On my mostly-defconfig kernel, this reduces kernel text size by ~1.3%. [1] https://github.com/dynup/kpatch/issues/1284 [2] https://gcc.gnu.org/pipermail/gcc-patches/2023-June/622872.html [3] https://gcc.gnu.org/pipermail/gcc-patches/2023-August/625986.html Compiler consideration: Gcc recently implemented an optimization [2] for loading symbols without explicit alignment, aligning with the IBM Z ELF ABI. This ABI mandates symbols to reside on a 2-byte boundary, enabling the use of the larl instruction. However, kernel linker scripts may still generate unaligned symbols. To address this, a new -munaligned-symbols option has been introduced [3] in recent gcc versions. This option has to be used with future gcc versions. Older Clang lacks support for handling unaligned symbols generated by kernel linker scripts when the kernel is built without -fPIE. However, future versions of Clang will include support for the -munaligned-symbols option. When the support is unavailable, compile the kernel with -fPIE to maintain the existing behavior. In addition to it: move vmlinux.relocs to safe relocation When the kernel is built with CONFIG_KERNEL_UNCOMPRESSED, the entire uncompressed vmlinux.bin is positioned in the bzImage decompressor image at the default kernel LMA of 0x100000, enabling it to be executed in-place. However, the size of .vmlinux.relocs could be large enough to cause an overlap with the uncompressed kernel at the address 0x100000. To address this issue, .vmlinux.relocs is positioned after the .rodata.compressed in the bzImage. Nevertheless, in this configuration, vmlinux.relocs will overlap with the .bss section of vmlinux.bin. To overcome that, move vmlinux.relocs to a safe location before clearing .bss and handling relocs. Compile warning fix from Sumanth Korikkar: When kernel is built with CONFIG_LD_ORPHAN_WARN and -fno-PIE, there are several warnings: ld: warning: orphan section `.rela.iplt' from `arch/s390/kernel/head64.o' being placed in section `.rela.dyn' ld: warning: orphan section `.rela.head.text' from `arch/s390/kernel/head64.o' being placed in section `.rela.dyn' ld: warning: orphan section `.rela.init.text' from `arch/s390/kernel/head64.o' being placed in section `.rela.dyn' ld: warning: orphan section `.rela.rodata.cst8' from `arch/s390/kernel/head64.o' being placed in section `.rela.dyn' Orphan sections are sections that exist in an object file but don't have a corresponding output section in the final executable. ld raises a warning when it identifies such sections. Eliminate the warning by placing all .rela orphan sections in .rela.dyn and raise an error when size of .rela.dyn is greater than zero. i.e. Dont just neglect orphan sections. This is similar to adjustment performed in x86, where kernel is built with -fno-PIE. commit 5354e84598f2 ("x86/build: Add asserts for unwanted sections") [sumanthk@linux.ibm.com: rebased Josh Poimboeuf patches and move vmlinux.relocs to safe location] [hca@linux.ibm.com: merged compile warning fix from Sumanth] Tested-by: Sumanth Korikkar Acked-by: Vasily Gorbik Signed-off-by: Josh Poimboeuf Signed-off-by: Sumanth Korikkar Link: https://lore.kernel.org/r/20240219132734.22881-4-sumanthk@linux.ibm.com Link: https://lore.kernel.org/r/20240219132734.22881-5-sumanthk@linux.ibm.com Signed-off-by: Heiko Carstens

s390/boot: vmlinux.lds.S: handle commonly discarded sections

2024-02-14T12:50:53Z

When building with CONFIG_LD_ORPHAN_WARN after selecting CONFIG_ARCH_HAS_LD_ORPHAN_WARN, there are several series of warnings from the various discardable sections that the kernel adds for build purposes that are not needed at runtime: s390-linux-ld: warning: orphan section `.export_symbol' from `arch/s390/boot/decompressor.o' being placed in section `.export_symbol' s390-linux-ld: warning: orphan section `.discard.addressable' from `arch/s390/boot/decompressor.o' being placed in section `.discard.addressable' s390-linux-ld: warning: orphan section `.modinfo' from `arch/s390/boot/decompressor.o' being placed in section `.modinfo' include/asm-generic/vmlinux.lds.h has a macro for easily discarding these sections across the kernel named COMMON_DISCARDS, use it to clear up the warnings. Signed-off-by: Nathan Chancellor Tested-by: Justin Stitt Link: https://lore.kernel.org/r/20240207-s390-lld-and-orphan-warn-v1-9-8a665b3346ab@kernel.org Signed-off-by: Heiko Carstens