From: Ard Biesheuvel <ardb@xxxxxxxxxx> The kexec purgatory is built like a kernel module, i.e., a partially linked ELF object where each section is allocated and placed individually, and all relocations need to be fixed up, even place relative ones. This makes sense for kernel modules, which share the address space with the core kernel, and contain unresolved references that need to be wired up to symbols in other modules or the kernel itself. The purgatory, however, is a fully linked binary without any external references, or any overlap with the kernel's virtual address space. So it makes much more sense to create a fully linked ELF executable that can just be loaded and run anywhere in memory. The purgatory build on x86 has already switched over to position independent codegen, which only leaves a handful of absolute references, which can either be dropped (patch #3) or converted into a RIP-relative one (patch #4). That leaves a purgatory executable that can run at any offset in memory with applying any relocations whatsoever. Some tweaks are needed to deal with the difference between partially (ET_REL) and fully (ET_DYN/ET_EXEC) linked ELF objects, but with those in place, a substantial amount of complicated ELF allocation, placement and patching/relocation code can simply be dropped. The last patch in the series removes this code from the generic kexec implementation, but this can only be done once other architectures apply the same changes proposed here for x86 (powerpc, s390 and riscv all implement the purgatory using the shared logic) Link: https://lore.kernel.org/all/CAKwvOd=3Jrzju++=Ve61=ZdeshxUM=K3-bGMNREnGOQgNw=aag@xxxxxxxxxxxxxx/ Link: https://lore.kernel.org/all/20240418201705.3673200-2-ardb+git@xxxxxxxxxx/ Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> Cc: kexec@xxxxxxxxxxxxxxxxxxx Cc: Nathan Chancellor <nathan@xxxxxxxxxx> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Bill Wendling <morbo@xxxxxxxxxx> Cc: Justin Stitt <justinstitt@xxxxxxxxxx> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Ard Biesheuvel (9): x86/purgatory: Drop function entry padding from purgatory x86/purgatory: Simplify stack handling x86/purgatory: Drop pointless GDT switch x86/purgatory: Avoid absolute reference to GDT x86/purgatory: Simplify GDT and drop data segment kexec: Add support for fully linked purgatory executables x86/purgatory: Use fully linked PIE ELF executable x86/purgatory: Simplify references to regs array kexec: Drop support for partially linked purgatory executables arch/x86/include/asm/kexec.h | 8 - arch/x86/kernel/kexec-bzimage64.c | 8 - arch/x86/kernel/machine_kexec_64.c | 127 ---------- arch/x86/purgatory/Makefile | 17 +- arch/x86/purgatory/entry64.S | 96 ++++---- arch/x86/purgatory/setup-x86_64.S | 31 +-- arch/x86/purgatory/stack.S | 18 -- include/asm-generic/purgatory.lds | 34 +++ kernel/kexec_file.c | 255 +++----------------- 9 files changed, 125 insertions(+), 469 deletions(-) delete mode 100644 arch/x86/purgatory/stack.S create mode 100644 include/asm-generic/purgatory.lds -- 2.44.0.769.g3c40516874-goog _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
