linux-kernel - Re: [Part2 PATCH v6 32/38] KVM: SVM: Add support for SEV DEBUG

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Date:   Mon, 30 Oct 2017 16:12:30 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Part2 PATCH v6 32/38] KVM: SVM: Add support for SEV
 DEBUG_DECRYPT command

On Mon, Oct 30, 2017 at 08:56:13AM -0500, Brijesh Singh wrote:
> I am not able to reproduce the build warning in my setup, what config
> option or compiler you are using to  trigger this issue ?

gcc7 has gotten smarter.

> I am on Fedora with gcc 6.4.x. Logically, the code looks okay. I can
> try to rearrange code to fix the warning. I have not touched this
> function since couple of rev, have u seen similar warning in previous
> versions (v5, v4 etc). thanks

Lemme see:

sev_dbg_crypt() does

                ret = __sev_dbg_decrypt(kvm,
                                       __sme_page_pa(src_p[0]) + s_off,
                                       dst_vaddr, 0,
                                       __sme_page_pa(dst_p[0]) + d_off,
                                       len, &argp->error);

and that 4th argument is 0. IINM, that's dst_kaddr and you're doing

	memcpy((void *)dst_kaddr, page_address(tpage) + offset, size);
		^^^^^^^^^^^^^^^^

BOOM!

-- 
Regards/Gruss,
    Boris.

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