linux-kernel - Re: AMD microcode loading broken on 32 bit

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Date:	Thu, 30 Jan 2014 16:13:21 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: AMD microcode loading broken on 32 bit

On Wed, Jan 29, 2014 at 12:22:19AM +0100, Borislav Petkov wrote:
> > >Are you sure that
> > >
> > >    container = (u8 *)(__va((u32)relocated_ramdisk) +
> > >                           ((u32)container -
> > >boot_params.hdr.ramdisk_image));
> > >
> > >in save_microcode_in_initrd_amd() always results in a valid
> > >pointer? It is non-NULL but it
> > >points to address that looks to be not mapped.

Well, here's what I see here:

* initrd *without* microcode:

[    0.000000] RAMDISK: [mem 0x7fbfc000-0x7ffeffff]
[    0.000000] Allocated new RAMDISK: [mem 0x3680a000-0x36bfd099]
[    0.000000] Move RAMDISK from [mem 0x7fbfc000-0x7ffef099] to [mem 0x3680a000-0x36bfd099]

...

[    0.710771] save_microcode_in_initrd_amd:

relocated_ramdisk:			0x3680a000,
__va(relocated_ramdisk):		0xf680a000,
container:				0x76c0e000,
boot_params.hdr.ramdisk_image:		0x7fbfc000

...

[    0.717080] BUG: unable to handle kernel paging request at 76c0e008


* initrd + microcode:

[    0.000000] RAMDISK: [mem 0x7fbf7000-0x7ffeffff]
[    0.000000] Allocated new RAMDISK: [mem 0x36805000-0x36bfd499]
[    0.000000] Move RAMDISK from [mem 0x7fbf7000-0x7ffef499] to [mem 0x36805000-0x36bfd499]

[    0.781948] save_microcode_in_initrd_amd:

relocated_ramdisk:			0x36805000,
__va(relocated_ramdisk):		0xf6805000,
container:				0xf680527c,
boot_params.hdr.ramdisk_image:		0x7fbf7000

Now guess what happens arithmetically if container is 0 (first case
above without microcode):

0xf680a000 + 0 - 0x7fbfc000 = 0x76c0e000.

So the fix of looking at ucode_cpio.data is correct.

An equivalent fix would be this hunk below but the initial version I
sent you aligns more with what we do on 64-bit.

---
diff --git a/arch/x86/kernel/cpu/microcode/amd_early.c b/arch/x86/kernel/cpu/microcode/amd_early.c
index 8384c0fa206f..7199953fdbf2 100644
--- a/arch/x86/kernel/cpu/microcode/amd_early.c
+++ b/arch/x86/kernel/cpu/microcode/amd_early.c
@@ -347,6 +347,9 @@ int __init save_microcode_in_initrd_amd(void)
        if (!uci->cpu_sig.sig)
                smp_call_function_single(bsp, collect_cpu_sig_on_bsp, NULL, 1);
 
+       if (!container)
+               return -EINVAL;
+
        /*
         * Take into account the fact that the ramdisk might get relocated
         * and therefore we need to recompute the container's position in

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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