From: Peter Zijlstra <peterz@infradead.org>
To: Borislav Petkov <bp@suse.de>
Cc: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org,
x86@kernel.org, ardb@kernel.org, tglx@linutronix.de,
gregkh@linuxfoundation.org, torvalds@linux-foundation.org,
Guenter Roeck <linux@roeck-us.net>,
Josh Poimboeuf <jpoimboe@kernel.org>,
stable@vger.kernel.org, Andrew Cooper <Andrew.Cooper3@citrix.com>
Subject: Re: [PATCH] efi/x86: use naked RET on mixed mode call wrapper
Date: Mon, 18 Jul 2022 18:38:35 +0200 [thread overview]
Message-ID: <YtWMiyem8+N4vbKE@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <YtWKK2ZLib1R7itI@zn.tnic>
On Mon, Jul 18, 2022 at 06:28:27PM +0200, Borislav Petkov wrote:
> On Mon, Jul 18, 2022 at 01:41:37PM +0200, Peter Zijlstra wrote:
> > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> > index 10a3bfc1eb23..f934dcdb7c0d 100644
> > --- a/arch/x86/include/asm/nospec-branch.h
> > +++ b/arch/x86/include/asm/nospec-branch.h
> > @@ -297,6 +297,8 @@ do { \
> > alternative_msr_write(MSR_IA32_SPEC_CTRL, \
> > spec_ctrl_current() | SPEC_CTRL_IBRS, \
> > X86_FEATURE_USE_IBRS_FW); \
> > + altnerative_msr_write(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, \
> > + X86_FEATURE_USE_IBPB_FW); \
> > } while (0)
>
> So I'm being told we need to untrain on return from EFI to protect the
> kernel from it. Ontop of yours.
I don't think there's any credible way we can protect against EFI taking
over the system if it wants to. It runs at CPL0 and has access to the
direct map. If EFI wants it can take over the system without trying.
next prev parent reply other threads:[~2022-07-18 16:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 19:45 [PATCH] efi/x86: use naked RET on mixed mode call wrapper Thadeu Lima de Souza Cascardo
2022-07-15 22:51 ` Guenter Roeck
2022-07-18 11:41 ` Peter Zijlstra
2022-07-18 13:59 ` Thadeu Lima de Souza Cascardo
2022-07-18 16:10 ` Peter Zijlstra
2022-07-18 16:28 ` Borislav Petkov
2022-07-18 16:38 ` Peter Zijlstra [this message]
2022-07-18 17:19 ` Andrew Cooper
2022-07-18 18:34 ` Linus Torvalds
2022-07-18 18:46 ` Borislav Petkov
2022-07-19 15:22 ` Ard Biesheuvel
2022-07-19 17:37 ` Borislav Petkov
2022-07-19 19:45 ` [tip: x86/urgent] x86/amd: Use IBPB for firmware calls tip-bot2 for Peter Zijlstra
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