linux-kernel - Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls in _

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Message-ID: <eac239fe-a420-4bc7-a792-207df9f847d3@zytor.com>
Date: Thu, 1 May 2025 23:12:52 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>, "H. Peter Anvin" <hpa@...or.com>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com, ardb@...nel.org,
        kees@...nel.org, Arnd Bergmann <arnd@...db.de>,
        gregkh@...uxfoundation.org, jpoimboe@...nel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-efi@...r.kernel.org,
        samitolvanen@...gle.com, ojeda@...nel.org
Subject: Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls in
 __nocfi functions

On 5/1/2025 11:59 AM, Sean Christopherson wrote:
>> Ok maybe I'm being dense, but what is left other than simply calling
>> __fred_entry_from_kvm() as a normal C function?
>>
>> I'm on the go so there might be something in the code I'm missing, but on the
>> surface...?
> I'm sure it's doable, though I'd be more than a little nervous about diverging
> from what FRED=y does, e.g. in case code somewhere expects the stack to look
> exactly like a real FRED event.

__fred_entry_from_kvm() accepts a pt_regs structure pointer, with event
type and vector in FRED stack frame.  They are set up in the assembly.

> And since we'd still need the assembly to support FRED=y, I don't see any point
> in adding more code when it's trivially easy to have asm_fred_entry_from_kvm()
> skip ERETS.

Yeah, your change seems minimized to me.