From: Peter Zijlstra <peterz@infradead.org>
To: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
jpoimboe@redhat.com, jthierry@redhat.com, tglx@linutronix.de
Subject: Re: [PATCH V3 5/9] objtool: Add return address unwind hints
Date: Tue, 14 Apr 2020 21:48:01 +0200 [thread overview]
Message-ID: <20200414194801.GH2483@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <ed46281f-46e5-10a0-1b61-60a54ea9d84e@oracle.com>
On Tue, Apr 14, 2020 at 09:27:27PM +0200, Alexandre Chartre wrote:
> This provides a generic code to handle any intra-function call. Currently we have
> the RSB stuffing ones which are forgotten with the UNWIND_HINT_TYPE_RADDR_DELETE
> directive. And for retpoline, they will not return if we have an indirect jump
> (JMP_NOSPEC) but they will return if we have an indirect call (CALL_NOSPEC). The
> code can handle both cases. For example, if we were to have a CALL_NOSPEC invocation
> which is not in an alternative then objtool can now correctly handle it.
The specialness of CALL_NOSPEC goes away with my proposed retpoline
rework as well. I really don't think we need something as complicated as
this.
Fundamentally validate_branch() will continue after a CALL instruction;
so I'm thikning the worst that can happen from not following a
(theoretical direct return) is a false-positive unreachable code
warning, and we can trivially fix those with exisiting hints.
next prev parent reply other threads:[~2020-04-14 19:50 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 10:36 [PATCH V3 0/9] objtool changes to check retpoline code Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 1/9] objtool: is_fentry_call() crashes if call has no destination Alexandre Chartre
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 2/9] objtool: Allow branches within the same alternative Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 3/9] objtool: Add support for intra-function calls Alexandre Chartre
2020-04-14 12:07 ` Julien Thierry
2020-04-16 12:12 ` Miroslav Benes
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 4/9] objtool: Handle return instruction with intra-function call Alexandre Chartre
2020-04-14 13:44 ` Julien Thierry
2020-04-14 10:36 ` [PATCH V3 5/9] objtool: Add return address unwind hints Alexandre Chartre
2020-04-14 16:16 ` Peter Zijlstra
2020-04-14 16:40 ` Alexandre Chartre
2020-04-14 17:56 ` Peter Zijlstra
2020-04-14 18:31 ` Alexandre Chartre
2020-04-14 18:42 ` Peter Zijlstra
2020-04-14 19:27 ` Alexandre Chartre
2020-04-14 19:48 ` Peter Zijlstra [this message]
2020-04-14 10:36 ` [PATCH V3 6/9] objtool: Report inconsistent stack changes in alternative Alexandre Chartre
2020-04-14 15:35 ` Julien Thierry
2020-04-14 22:41 ` kbuild test robot
2020-04-14 23:09 ` kbuild test robot
2020-04-16 14:18 ` Peter Zijlstra
2020-04-16 14:43 ` Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 7/9] x86/speculation: Change __FILL_RETURN_BUFFER to work with objtool Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 8/9] x86/speculation: Add return address unwind hints to retpoline and RSB stuffing Alexandre Chartre
2020-04-14 10:36 ` [PATCH V3 9/9] x86/speculation: Annotate intra-function calls Alexandre Chartre
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