From: Julien Thierry <jthierry@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
tglx@linutronix.de, linux-kernel@vger.kernel.org, x86@kernel.org,
mhiramat@kernel.org, mbenes@suse.cz,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET
Date: Thu, 2 Apr 2020 07:56:18 +0100 [thread overview]
Message-ID: <39ab6c97-bdab-bc39-7a3c-864cad2bc2de@redhat.com> (raw)
In-Reply-To: <684d6e29-4a01-b4a5-f906-7bdee5ad108f@redhat.com>
On 4/2/20 7:41 AM, Julien Thierry wrote:
>
>
> On 4/1/20 6:09 PM, Peter Zijlstra wrote:
>> On Wed, Apr 01, 2020 at 04:43:35PM +0100, Julien Thierry wrote:
>>>> + return true;
>>>> +
>>>> + if (state->stack_size != initial_func_cfi.cfa.offset + ret_offset)
>>>> return true;
>>>>
>>>> - for (i = 0; i < CFI_NUM_REGS; i++)
>>>> + for (i = 0; i < CFI_NUM_REGS; i++) {
>>>> if (state->regs[i].base != initial_func_cfi.regs[i].base ||
>>>> state->regs[i].offset !=
>>>> initial_func_cfi.regs[i].offset)
>>>> return true;
>>>> + }
>>>>
>>>> return false;
>>>> }
>>
>>>> @@ -2185,6 +2148,13 @@ static int validate_branch(struct objtoo
>>>>
>>>> break;
>>>>
>>>> + case INSN_EXCEPTION_RETURN:
>>>> + if (func) {
>>>> + state.stack_size -= arch_exception_frame_size;
>>>> + break;
>>>
>>> Why break instead of returning? Shouldn't an exception return mark
>>> the end
>>> of a branch (whether inside or outside a function) ?
>>>
>>> Here it seems it will continue to the next instruction which might
>>> have been
>>> unreachable.
>>
>> The code in question (x86's sync_core()), is an exception return to
>> self. It pushes an exception frame that points to right after the
>> exception return instruction.
>>
>> This is the only usage of IRET in STT_FUNC symbols.
>>
>> So rather than teaching objtool how to interpret the whole
>> push;push;push;push;push;iret sequence, teach it how big the frame is
>> (arch_exception_frame_size) and let it continue.
>>
>> All the other (real) IRETs are in STT_NOTYPE in the entry assembly.
>>
>
> Right, I see.. However I'm not completely convinced by this. I must
> admit I haven't followed the whole conversation, but what was the issue
> with the HINT_IRET_SELF? It seemed more elegant, but I might be missing
> some context.
>
> Otherwise, it might be worth having a comment in the code to point that
> this only handles the sync_core() case.
>
>
> Also, instead of adding a special "arch_exception_frame_size", I could
> suggest:
> - Picking this patch [1] from a completely arbitrary source
> - Getting rid of INSN_STACK type, any instruction could then include
> stack ops on top of their existing semantics, they can just have an
> empty list if they don't touch SP/BP
> - x86 decoder adds a stack_op to the iret to modify the stack pointer by
> the right amount
>
And the x86 decode could also lookup the symbol containing an IRET and
chose whether its type should be INSN_CONTEXT_SWITCH or INSN_OTHER
depending on whether the symbol is a function or not.
This would avoid having the arch specific pattern detected the generic
stack validation part of objtool.
--
Julien Thierry
next prev parent reply other threads:[~2020-04-02 6:56 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 17:45 [PATCH v4 00/13] objtool: vmlinux.o and moinstr validation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 01/13] objtool: Remove CFI save/restore special case Peter Zijlstra
2020-03-26 11:30 ` Peter Zijlstra
2020-03-26 12:58 ` Peter Zijlstra
2020-03-26 13:44 ` Josh Poimboeuf
2020-03-26 15:38 ` Peter Zijlstra
2020-03-27 4:19 ` Josh Poimboeuf
2020-03-26 14:44 ` Miroslav Benes
2020-03-26 15:04 ` Miroslav Benes
2020-03-26 13:00 ` Peter Zijlstra
2020-03-26 13:56 ` Josh Poimboeuf
2020-03-26 15:49 ` Peter Zijlstra
2020-03-26 19:57 ` Peter Zijlstra
2020-03-27 1:00 ` Josh Poimboeuf
2020-03-30 17:02 ` Peter Zijlstra
2020-03-30 19:02 ` Josh Poimboeuf
2020-03-30 20:02 ` Peter Zijlstra
2020-03-30 20:29 ` Peter Zijlstra
2020-03-31 11:16 ` [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET Peter Zijlstra
2020-03-31 15:31 ` Steven Rostedt
2020-03-31 16:06 ` [RFC][PATCH] x86,ftrace: Shrink ftrace_regs_caller() by one byte Peter Zijlstra
2020-03-31 19:58 ` [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET Peter Zijlstra
2020-03-31 20:26 ` Josh Poimboeuf
2020-03-31 20:23 ` Josh Poimboeuf
2020-03-31 20:40 ` Peter Zijlstra
2020-03-31 21:07 ` Peter Zijlstra
2020-03-31 21:17 ` Josh Poimboeuf
2020-03-31 21:20 ` Josh Poimboeuf
2020-03-31 22:27 ` [PATCH v2] " Peter Zijlstra
2020-04-01 14:14 ` Josh Poimboeuf
2020-04-01 14:22 ` Peter Zijlstra
2020-04-01 14:39 ` Josh Poimboeuf
2020-04-01 15:38 ` Peter Zijlstra
2020-04-01 15:39 ` Steven Rostedt
2020-04-01 15:43 ` Julien Thierry
2020-04-01 17:09 ` Peter Zijlstra
2020-04-01 17:33 ` Steven Rostedt
2020-04-01 17:45 ` Peter Zijlstra
2020-04-01 18:20 ` Steven Rostedt
2020-04-01 20:20 ` Peter Zijlstra
2020-04-01 17:37 ` Josh Poimboeuf
2020-04-02 6:41 ` Julien Thierry
2020-04-02 6:56 ` Julien Thierry [this message]
2020-04-02 7:50 ` Peter Zijlstra
2020-04-02 8:16 ` Julien Thierry
2020-04-02 8:17 ` Peter Zijlstra
2020-04-02 8:29 ` Julien Thierry
2020-04-02 8:58 ` Miroslav Benes
2020-03-25 17:45 ` [PATCH v4 02/13] objtool: Factor out CFI hints Peter Zijlstra
2020-03-25 18:26 ` Miroslav Benes
2020-03-25 19:41 ` Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 03/13] objtool: Rename struct cfi_state Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 04/13] objtool: Fix !CFI insn_state propagation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 05/13] objtool: Implement noinstr validation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 06/13] objtool: Optimize !vmlinux.o again Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 07/13] objtool: Use sec_offset_hash() for insn_hash Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 08/13] objtool: Detect loading function pointers across noinstr Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 09/13] kbuild/objtool: Add objtool-vmlinux.o pass Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 10/13] objtool: Avoid iterating !text section symbols Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 11/13] objtool: Rearrange validate_section() Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 12/13] objtool: Add STT_NOTYPE noinstr validation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 13/13] objtool: Also consider .entry.text as noinstr Peter Zijlstra
2020-03-25 19:03 ` [PATCH v4 00/13] objtool: vmlinux.o and moinstr validation Miroslav Benes
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