linux-kernel - Re: [PATCH RFC 00/43] x86/pie: Make kernel image's virtual address flexible

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Message-ID: <20230506071906.GA99736@k08j02272.eu95sqa>
Date:   Sat, 06 May 2023 15:19:06 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     <linux-kernel@...r.kernel.org>,
        "Thomas Garnier" <thgarnie@...omium.org>,
        "Lai Jiangshan" <jiangshan.ljs@...group.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Tom Rix" <trix@...hat.com>, <bpf@...r.kernel.org>,
        <llvm@...ts.linux.dev>
Subject: Re: [PATCH RFC 00/43] x86/pie: Make kernel image's virtual address
 flexible

On Fri, Apr 28, 2023 at 11:22:06PM +0800, Peter Zijlstra wrote:
> 
> For some raison I didn't get 0/n but did get all of the others. Please
> keep your Cc list consistent.
>
Sorry, I'll pay attention next time.
 
> On Fri, Apr 28, 2023 at 05:50:40PM +0800, Hou Wenlong wrote:
> 
> >   - It is not allowed to reference global variables in an alternative
> >     section since RIP-relative addressing is not fixed in
> >     apply_alternatives(). Fortunately, all disallowed relocations in the
> >     alternative section can be captured by objtool. I believe that this
> >     issue can also be fixed by using objtool.
> 
> https://lkml.kernel.org/r/Y9py2a5Xw0xbB8ou@hirez.programming.kicks-ass.net

Thank you for your patch. However, it's more complicated for call depth
tracking case. Although, the per-cpu variable in the alternative section
is relocated, but the content of the "skl_call_thunk_template" is copied
into another place, so the offset is still incorrect. I'm not sure if
this case is common or not. Since the destination is clear, I could do
relocation here as well, but it would make the code more complicated.

Thanks!