linux-kernel - Re: [PATCH v4 2/5] x86/alternative: add indirect call patching

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Message-ID: <20231114134715.GBZVN6Y97XrLQ4cbSL@fat_crate.local>
Date:   Tue, 14 Nov 2023 14:47:15 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v4 2/5] x86/alternative: add indirect call patching

On Tue, Nov 14, 2023 at 01:50:28PM +0100, Peter Zijlstra wrote:
> This loads the function target from the pv_ops table. We can't otherwise
> do this.

On Tue, Nov 14, 2023 at 01:56:37PM +0100, Juergen Gross wrote:
> It is replacing an _indirect_ call with a _direct_ one, taking the
> call target from the pointer used by the indirect call.

Then this is not just a ALT_FLAG_CALL. This is something special. The
flag definition needs a better name along with an explanation what it
does, perhaps best with an example from the final vmlinux - not from the
object file:

call   *0x0(%rip)

==>

call   *0x0

where the offsets haven't been linked in yet.

If this is going into the generic infrastructure, then it better be
explained properly so that other stuff can potentially use it too.

Thx.

-- 
Regards/Gruss,
    Boris.

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