On Tue, Oct 24, 2023 at 11:28:18PM -0700, Pawan Gupta wrote: > With .text.entry section I am getting getting below warnings and an > error: > > ----------------------------------------------------------------- > LD vmlinux.o > vmlinux.o: warning: objtool: .text.entry+0x0: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x40: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x80: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0xc0: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x100: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x140: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x180: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x1c0: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x200: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x240: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x280: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x2c0: unreachable instruction > vmlinux.o: warning: objtool: .text.entry+0x300: unreachable instruction > vmlinux.o: warning: objtool: .altinstr_replacement+0x2c: relocation to !ENDBR: .text.entry+0x0 > vmlinux.o: warning: objtool: .altinstr_replacement+0x1c4: relocation to !ENDBR: .text.entry+0x0 > vmlinux.o: warning: objtool: .altinstr_replacement+0x1d0: relocation to !ENDBR: .text.entry+0x0 > vmlinux.o: warning: objtool: .altinstr_replacement+0x2d2: relocation to !ENDBR: .text.entry+0x80 > vmlinux.o: warning: objtool: .altinstr_replacement+0x5d5: relocation to !ENDBR: .text.entry+0xc0 > OBJCOPY modules.builtin.modinfo > GEN modules.builtin > MODPOST vmlinux.symvers > UPD include/generated/utsversion.h > CC init/version-timestamp.o > LD .tmp_vmlinux.kallsyms1 > ld: error: unplaced orphan section `.text.entry' from `vmlinux.o' > make[2]: *** [scripts/Makefile.vmlinux:36: vmlinux] Error 1 > ----------------------------------------------------------------- > > ... because my config has CONFIG_LD_ORPHAN_WARN_LEVEL="error" and > objtool needs to be told about this entry. > > Do you think its worth fighting these warnings and error, or simply use > .rodata section for verw memory operand? I'm thinking you need to at the very least stay in a section that's actually still mapped with PTI :-) .entry.text is the only thing that is reliably mapped with PTI (IIRC), some configs also get a chunk of the kernel image, but not all. Something like the below should do I suppose. --- arch/x86/entry/entry.S | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S index bfb7bcb362bc..9eb2b532c92a 100644 --- a/arch/x86/entry/entry.S +++ b/arch/x86/entry/entry.S @@ -6,6 +6,8 @@ #include <linux/linkage.h> #include <asm/export.h> #include <asm/msr-index.h> +#include <asm/unwind_hints.h> +#include <asm/segment.h> .pushsection .noinstr.text, "ax" @@ -20,3 +22,16 @@ SYM_FUNC_END(entry_ibpb) EXPORT_SYMBOL_GPL(entry_ibpb); .popsection + +.pushsection .entry.text, "ax" + +.align 64 +SYM_CODE_START_NOALIGN(mds_verw_sel) + UNWIND_HINT_UNDEFINED + ANNOTATE_NOENDBR +1: + .word __KERNEL_DS + .skip 64 - (. - 1b), 0xcc +SYM_CODE_END(mds_verw_sel); + +.popsection
