linux-kernel - Re: [PATCH] x86/sev-es: Fix SEV-ES OUT/IN immediate opcode vc handling

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Date:   Tue, 29 Dec 2020 11:56:18 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Peter Gonda <pgonda@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] x86/sev-es: Fix SEV-ES OUT/IN immediate opcode vc
 handling

On Mon, Dec 28, 2020 at 03:43:06PM -0800, Sean Christopherson wrote:
> Eh, casting to u8 is "absolutely correct" as well.  I don't like using bytes[]
> because it feels like accessing the raw data as opposed to the end result of
> decoding, but it's not a sticking point.

Ok, code in the kernel uses mostly ->value so u8 casting it is.

> Yes, insn_get_immediate() sets insn->immediate.value directly and sign extends
> the imm8 (which is correct, e.g. for "AND r/m64, imm8"). 
> 
> 	switch (inat_immediate_size(insn->attr)) {
> 	case INAT_IMM_BYTE:
> 		insn->immediate.value = get_next(signed char, insn);
> 		insn->immediate.nbytes = 1;

Ah, there it is. And we set nbytes too, conveniently.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette