From: Peter Zijlstra <peterz@infradead.org>
To: Joerg Roedel <joro@8bytes.org>
Cc: x86@kernel.org, Joerg Roedel <jroedel@suse.de>,
hpa@zytor.com, Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Jiri Slaby <jslaby@suse.cz>,
Dan Williams <dan.j.williams@intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Juergen Gross <jgross@suse.com>,
Kees Cook <keescook@chromium.org>,
David Rientjes <rientjes@google.com>,
Cfir Cohen <cfir@google.com>, Erdem Aktas <erdemaktas@google.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mike Stunes <mstunes@vmware.com>,
Sean Christopherson <seanjc@google.com>,
Martin Radev <martin.b.radev@gmail.com>,
Arvind Sankar <nivedita@alum.mit.edu>,
linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v4 3/6] x86/sev-es: Split up runtime #VC handler for correct state tracking
Date: Thu, 10 Jun 2021 12:19:43 +0200 [thread overview]
Message-ID: <YMHnP1qgvznyYazv@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210610091141.30322-4-joro@8bytes.org>
Bah, I suppose the trouble is that this SEV crap requires PARAVIRT?
I should really get around to fixing noinstr validation with PARAVIRT on
:-(
On Thu, Jun 10, 2021 at 11:11:38AM +0200, Joerg Roedel wrote:
> +static void vc_handle_from_kernel(struct pt_regs *regs, unsigned long error_code)
static noinstr ...
> +{
> + irqentry_state_t irq_state = irqentry_nmi_enter(regs);
>
> + instrumentation_begin();
>
> + if (!vc_raw_handle_exception(regs, error_code)) {
> /* Show some debug info */
> show_regs(regs);
>
> @@ -1434,7 +1400,59 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
> panic("Returned from Terminate-Request to Hypervisor\n");
> }
>
> + instrumentation_end();
> + irqentry_nmi_exit(regs, irq_state);
> +}
> +
> +static void vc_handle_from_user(struct pt_regs *regs, unsigned long error_code)
static noinstr ...
> +{
> + irqentry_state_t irq_state = irqentry_enter(regs);
> +
> + instrumentation_begin();
> +
> + if (!vc_raw_handle_exception(regs, error_code)) {
> + /*
> + * Do not kill the machine if user-space triggered the
> + * exception. Send SIGBUS instead and let user-space deal with
> + * it.
> + */
> + force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
> + }
> +
> + instrumentation_end();
> + irqentry_exit(regs, irq_state);
> +}
+ linebreak
> +/*
> + * Main #VC exception handler. It is called when the entry code was able to
> + * switch off the IST to a safe kernel stack.
> + *
> + * With the current implementation it is always possible to switch to a safe
> + * stack because #VC exceptions only happen at known places, like intercepted
> + * instructions or accesses to MMIO areas/IO ports. They can also happen with
> + * code instrumentation when the hypervisor intercepts #DB, but the critical
> + * paths are forbidden to be instrumented, so #DB exceptions currently also
> + * only happen in safe places.
> + */
> +DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
> +{
> + /*
> + * Handle #DB before calling into !noinstr code to avoid recursive #DB.
> + */
> + if (error_code == SVM_EXIT_EXCP_BASE + X86_TRAP_DB) {
> + vc_handle_trap_db(regs);
> + return;
> + }
> +
> + /*
> + * This is invoked through an interrupt gate, so IRQs are disabled. The
> + * code below might walk page-tables for user or kernel addresses, so
> + * keep the IRQs disabled to protect us against concurrent TLB flushes.
> + */
> +
> + if (user_mode(regs))
> + vc_handle_from_user(regs, error_code);
> + else
> + vc_handle_from_kernel(regs, error_code);
> }
#DB and MCE use idtentry_mce_db and split out in asm. When I look at
idtentry_vc, it appears to me that VC_SAFE_STACK already implies
from-user, or am I reading that wrong?
Ah, it appears you're muddling things up again by then also calling
safe_stack_ from exc_.
How about you don't do that and have exc_ call your new from_kernel
function, then we know that safe_stack_ is always from-user. Then also
maybe do:
s/VS_SAFE_STACK/VC_USER/
s/safe_stack_/noist_/
to match all the others (#DB/MCE).
Also, AFAICT, you don't actually need DEFINE_IDTENTRY_VC_IST, it doesn't
have an ASM counterpart.
So then you end up with something like:
DEFINE_IDTENTRY_VC(exc_vc)
{
if (unlikely(on_vc_fallback_stack(regs))) {
instrumentation_begin();
panic("boohooo\n");
instrumentation_end();
}
vc_from_kernel();
}
DEFINE_IDTENTRY_VC_USER(exc_vc)
{
vc_from_user();
}
Which is, I'm thinking, much simpler, no?
next prev parent reply other threads:[~2021-06-10 10:21 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 9:11 [PATCH v4 0/6] x86/sev-es: Fixes for SEV-ES Guest Support Joerg Roedel
2021-06-10 9:11 ` [PATCH v4 1/6] x86/sev-es: Fix error message in runtime #VC handler Joerg Roedel
2021-06-10 9:11 ` [PATCH v4 2/6] x86/sev-es: Disable IRQs while GHCB is active Joerg Roedel
2021-06-11 14:05 ` Borislav Petkov
2021-06-11 14:20 ` Joerg Roedel
2021-06-11 14:34 ` Borislav Petkov
2021-06-10 9:11 ` [PATCH v4 3/6] x86/sev-es: Split up runtime #VC handler for correct state tracking Joerg Roedel
2021-06-10 10:19 ` Peter Zijlstra [this message]
2021-06-10 11:30 ` Joerg Roedel
2021-06-10 9:11 ` [PATCH v4 4/6] x86/insn-eval: Make 0 a valid RIP for insn_get_effective_ip() Joerg Roedel
2021-06-10 9:11 ` [PATCH v4 5/6] x86/insn: Extend error reporting from insn_fetch_from_user[_inatomic]() Joerg Roedel
2021-06-10 9:11 ` [PATCH v4 6/6] x86/sev-es: Propagate #GP if getting linear instruction address failed Joerg Roedel
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