linux-kernel - Re: [PATCH] x86/microcode: Do not access the initrd after it has been freed

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Message-ID: <20170131074355.GA17636@gmail.com>
Date:   Tue, 31 Jan 2017 08:43:55 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...en8.de>, Mike Galbraith <efault@....de>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/microcode: Do not access the initrd after it has
 been freed


(Cc:-ed Mike as this could explain his early boot crash/hang?
        Mike: please try -tip f18a8a0143b1 that I just pushed out. )

* Borislav Petkov <bp@...en8.de> wrote:

> On Mon, Jan 30, 2017 at 09:46:32AM +0100, Ingo Molnar wrote:
> > Ok, I have applied this to tip:x86/urgent.
> > 
> > Note that there are new conflicts with your pending work in tip:x86/microcode, and 
> > I fixed them up in:
> > 
> >   7c5b4112040e Merge branch 'x86/urgent' into x86/microcode, to resolve conflicts
> > 
> > Could you please double-check my conflict resolution?
> 
> Almost, this part is wrong:
> 
> --------------------- arch/x86/kernel/cpu/microcode/amd.c ---------------------
> index 7889ae492af0,079e81733a58..73082365ed1c
> @@@ -268,20 -316,43 +268,20 @@@ void __load_ucode_amd(unsigned int cpui
>   		use_pa	= false;
>   	}
>   
> - 	if (!get_builtin_microcode(&cp, x86_family(cpuid_1_eax)))
>  -	if (!get_builtin_microcode(&cp, family))
> ++	if (!get_builtin_microcode(&cp, x86_family(cpuid_1_eax)) && !initrd_gone)
>   		cp = find_microcode_in_initrd(path, use_pa);
> 
> --
> 
> Btw, I did experiment with the merging because I knew it'll cause
> trouble due to the urgent fix and here's what I did:
> 
> You're merging tip/x86/urgent into tip/x86/microcode so I checked out
> the microcode branch and did:
> 
> $ git checkout -b tip-microcode tip/x86/microcode
> $ git merge -s recursive -X ours tip/x86/urgent
> 
> This way I'm favouring our changes in the conflicting files. It merges
> cleanly and the resulting diff is below.

Nice - I've updated the branch with your resolution. Could you please 
double-check the double checked resolution?

> The logic behind it is is that tip/x86/microcode does away with a bunch
> of code and the urgent change touches some of that code but that's only
> for 4.10.
> 
> It goes away in 4.11 and that's why we should prefer "ours" as the merge
> option.
> 
> 	 [ Btw, I'll send a patch for 4.11 later to make initrd_gone static as
> 	   it is going to be used only in microcode/core.c after the cleanup. ]
> 
> However, I still haven't figured out how to say "prefer ours but only
> for specific files or subtree" because the diff has that hunk in
> arch/x86/kernel/fpu/core.c too which should definitely not be "ours" as
> it is a fix and there the urgent version should be the one going in.
> 
> Hmmm.

So the diff between your resolution and mine is attached below - now fpu/core.c 
changes, so I'm not sure why fpu/core.c is in your diff?

Thanks,

	Ingo

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 73082365ed1c..7889ae492af0 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -268,7 +268,7 @@ void __load_ucode_amd(unsigned int cpuid_1_eax, struct cpio_data *ret)
 		use_pa	= false;
 	}
 
-	if (!get_builtin_microcode(&cp, x86_family(cpuid_1_eax)) && !initrd_gone)
+	if (!get_builtin_microcode(&cp, x86_family(cpuid_1_eax)))
 		cp = find_microcode_in_initrd(path, use_pa);
 
 	/* Needed in load_microcode_amd() */
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index e51eeaed8016..b4a4cd39b358 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -230,7 +230,7 @@ static int __init save_microcode_in_initrd(void)
 		break;
 	case X86_VENDOR_AMD:
 		if (c->x86 >= 0x10)
-			ret = save_microcode_in_initrd_amd(cpuid_eax(1));
+			return save_microcode_in_initrd_amd(cpuid_eax(1));
 		break;
 	default:
 		break;