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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.


  reply	other threads:[~2020-04-14 19:50 UTC|newest]

Thread overview: 29+ 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 22:41     ` kbuild test robot
2020-04-14 23:09   ` 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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