linux-kernel - Re: [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200331210720.GG2452@worktop.programming.kicks-ass.net>
Date:   Tue, 31 Mar 2020 23:07:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org, x86@...nel.org,
        mhiramat@...nel.org, mbenes@...e.cz,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET

On Tue, Mar 31, 2020 at 10:40:47PM +0200, Peter Zijlstra wrote:
> On Tue, Mar 31, 2020 at 03:23:15PM -0500, Josh Poimboeuf wrote:

> > I now understand what you're trying to do with the RET_TAIL thing, and I
> > guess it's ok for the ftrace case.  But I'd rather an UNWIND_HINT_IGNORE
> > before the tail cail, which would tell objtool to just silence the tail
> > call warning.  It's simpler for the user to understand, it's simpler
> > logic in objtool, and I think an "ignore warnings for the next insn"
> > hint would be more generally applicable anyway.
> 
> I like how this is specific on how far the stack can be off, as opposed
> so say 'ignore any warning on this instruction'.
> 
> Because by saying this RET should be +8, we'll still get a warning when
> this is not the case (and in fact I should strengthen the patch to
> implement that).

Like this; I'm confused on what cfa.offset is vs stack_size though.

But this way we're strict and always warn when the unexpected happens.

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1423,8 +1423,7 @@ static bool has_modified_stack_frame(str
 	    !(ret_offset && state->cfa.offset == initial_func_cfi.cfa.offset + ret_offset))
 		return true;
 
-	if (state->stack_size != initial_func_cfi.cfa.offset &&
-	    !(ret_offset && state->stack_size == initial_func_cfi.cfa.offset + ret_offset))
+	if (state->stack_size != initial_func_cfi.cfa.offset + ret_offset)
 		return true;
 
 	for (i = 0; i < CFI_NUM_REGS; i++) {