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Date: Sun, 6 Feb 2022 12:58:16 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Kees Cook <keescook@...omium.org> Cc: Alexander Popov <alex.popov@...ux.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Josh Poimboeuf <jpoimboe@...hat.com>, Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] gcc-plugins/stackleak: Use noinstr in favor of notrace On Tue, Feb 01, 2022 at 04:19:18PM -0800, Kees Cook wrote: > While the stackleak plugin was already using notrace, objtool is now a > bit more picky. Update the notrace uses to noinstr. Silences these > warnings: > > vmlinux.o: warning: objtool: do_syscall_64()+0x9: call to stackleak_track_stack() leaves .noinstr.text section > vmlinux.o: warning: objtool: do_int80_syscall_32()+0x9: call to stackleak_track_stack() leaves .noinstr.text section > vmlinux.o: warning: objtool: exc_general_protection()+0x22: call to stackleak_track_stack() leaves .noinstr.text section > vmlinux.o: warning: objtool: fixup_bad_iret()+0x20: call to stackleak_track_stack() leaves .noinstr.text section > vmlinux.o: warning: objtool: do_machine_check()+0x27: call to stackleak_track_stack() leaves .noinstr.text section > vmlinux.o: warning: objtool: .text+0x5346e: call to stackleak_erase() leaves .noinstr.text section > vmlinux.o: warning: objtool: .entry.text+0x143: call to stackleak_erase() leaves .noinstr.text section > vmlinux.o: warning: objtool: .entry.text+0x10eb: call to stackleak_erase() leaves .noinstr.text section > vmlinux.o: warning: objtool: .entry.text+0x17f9: call to stackleak_erase() leaves .noinstr.text section > > Cc: Alexander Popov <alex.popov@...ux.com> > Suggested-by: Peter Zijlstra <peterz@...radead.org> > Link: https://lore.kernel.org/lkml/YYENAKB0igNFnFmK@hirez.programming.kicks-ass.net/ > Signed-off-by: Kees Cook <keescook@...omium.org> > --- > Is it correct to exclude .noinstr.text here? That means any functions called in > there will have their stack utilization untracked. This doesn't seem right to me, > though. Shouldn't stackleak_track_stack() just be marked noinstr instead? This patch is right. stackleak_track_stack() cannot be marked noinstr becaues it accesses things that might not be there. Consider what happens if we pull the PTI page-table swap into the noinstr C part. > @@ -446,6 +447,8 @@ static bool stackleak_gate(void) > return false; > if (!strncmp(TREE_STRING_POINTER(section), ".meminit.text", 13)) > return false; > + if (!strncmp(TREE_STRING_POINTER(section), ".noinstr.text", 13)) > + return false; For paranoia's sake I'd like .entry.text added there as well. > } > > return track_frame_size >= 0;
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