From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Jon Kohler <jon@nutanix.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Daniel Sneddon <daniel.sneddon@linux.intel.com>,
"kvm @ vger . kernel . org" <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: VMX: remove LFENCE in vmx_spec_ctrl_restore_host()
Date: Mon, 5 Jun 2023 20:59:53 -0700 [thread overview]
Message-ID: <20230606035953.fssnnwkk2nd2jmqm@treble> (raw)
In-Reply-To: <790725a7-cde8-addb-c2e4-91827f70215e@citrix.com>
On Tue, Jun 06, 2023 at 01:20:52AM +0100, Andrew Cooper wrote:
<clip very useful summary which belongs in git somewhere>
> But, the safety of vmx_spec_ctrl_restore_host() in the first place
> depends on the early return never ever becoming a conditional,
Good point. And that would be easier to overlook in C.
> and the compiler never emitting a call to memcpy()/memset()/whatever
> behind your back - something which is not prohibited by noinstr.
Au contraire, objtool has checking for that:
if (state->noinstr && state->instr <= 0 &&
!noinstr_call_dest(file, insn, insn_call_dest(insn))) {
WARN_INSN(insn, "call to %s() leaves .noinstr.text section", call_dest_name(insn));
return 1;
}
Regardless, despite being the person who wrote this thing in C to begin
with, I believe asm really is a better fit due to the delicate and
precise nature of the mitigations.
--
Josh
next prev parent reply other threads:[~2023-06-06 4:00 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-31 15:01 [PATCH] KVM: VMX: remove LFENCE in vmx_spec_ctrl_restore_host() Jon Kohler
2023-05-31 23:18 ` Josh Poimboeuf
2023-05-31 23:58 ` Jon Kohler
2023-06-01 0:42 ` Josh Poimboeuf
2023-06-01 0:50 ` Andrew Cooper
2023-06-01 0:56 ` Josh Poimboeuf
2023-06-01 1:24 ` Pawan Gupta
2023-06-01 4:23 ` Josh Poimboeuf
2023-06-05 14:29 ` Jon Kohler
2023-06-05 16:35 ` Josh Poimboeuf
2023-06-05 16:39 ` Jon Kohler
2023-06-05 17:31 ` Pawan Gupta
2023-06-05 18:31 ` Sean Christopherson
2023-06-05 19:57 ` Jon Kohler
2023-06-05 20:01 ` Josh Poimboeuf
2023-06-06 0:20 ` Andrew Cooper
2023-06-06 3:59 ` Josh Poimboeuf [this message]
2023-06-01 0:29 ` Andrew Cooper
2023-06-01 0:53 ` Josh Poimboeuf
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