linux-kernel - Re: [PATCH 06/13] x86/microcode/AMD: Rework container parsing

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Date:   Wed, 18 Jan 2017 15:44:46 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/13] x86/microcode/AMD: Rework container parsing

On Wed, Jan 18, 2017 at 12:31:24AM +0100, Borislav Petkov wrote:
> Ah, good catch. I guess I'll have to do here:
> 
>                         /* Something corrupted the container, invalidate it. */
>                         eq_id = 0;
>                         break;
> 
> too.

Ok, I should've done the below from the beginning. I should be looking
at desc->mc which says whether we have found a patch or not. And then
prepare retvals accordingly.

The equivalence id (eq_id) is then used to signal that fact.

And in a future patch, I'll check desc->mc after that function returns
and not eq_id. (I had to do eq_id because of the global this_equiv_id
but that's gone now too).

        /*
         * Scan through the rest of the container to find where it ends. We do
         * some basic sanity-checking too.
         */
        while (size > 0) {
                struct microcode_amd *mc;
                u32 patch_size;

                hdr = (u32 *)buf;

                if (hdr[0] != UCODE_UCODE_TYPE)
                        break;

                /* Sanity-check patch size. */
                patch_size = hdr[1];
                if (patch_size > PATCH_MAX_SIZE)
                        break;

                /* Skip patch section header: */
                buf  += SECTION_HDR_SIZE;
                size -= SECTION_HDR_SIZE;

                mc = (struct microcode_amd *)buf;
                if (eq_id == mc->hdr.processor_rev_id) {
                        desc->psize = patch_size;
                        desc->mc = mc;
                }

                buf  += patch_size;
                size -= patch_size;
        }

        /*
         * If we have found a patch (desc->mc), it means we're looking at the
         * container which has a patch for this CPU so return 0 to mean, @ucode
         * already points to the proper container. Otherwise, we return the size
         * we scanned so that we can advance to the next container in the
         * buffer.
         */
        if (desc->mc) {
                desc->eq_id = eq_id;
                desc->data  = ucode;
                desc->size  = orig_size - size;

                return 0;
        }

-- 
Regards/Gruss,
    Boris.

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