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From: Joerg Roedel <jroedel@suse.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Tom Lendacky <Thomas.Lendacky@amd.com>,
	Mike Stunes <mstunes@vmware.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Juergen Gross <JGross@suse.com>,
	Jiri Slaby <jslaby@suse.cz>, Kees Cook <keescook@chromium.org>,
	kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Thomas Hellstrom <thellstrom@vmware.com>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	X86 ML <x86@kernel.org>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace)
Date: Tue, 23 Jun 2020 14:04:33 +0200	[thread overview]
Message-ID: <20200623120433.GB14101@suse.de> (raw)
In-Reply-To: <20200623114818.GD4817@hirez.programming.kicks-ass.net>

On Tue, Jun 23, 2020 at 01:48:18PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 23, 2020 at 01:30:07PM +0200, Joerg Roedel wrote:

> But you cannot do a recursion check in #VC, because the NMI can happen
> on the first instruction of #VC, before we can increment our counter,
> and then the #VC can happen on NMI because the IST stack is a goner, and
> we're fscked again (or on a per-cpu variable we touch in our elaborate
> NMI setup, etc..).

No, the recursion check is fine, because overwriting an already used IST
stack doesn't matter (as long as it can be detected) if we are going to
panic anyway. It doesn't matter because the kernel will not leave the
currently running handler anymore.

I agree there is no way to keep the system running if that happens, but
that is also not what is wanted. If stack recursion happens, something
malicious from the HV side is going on, and all the kernel needs to be
able to is to safely and reliably detect the situation and panic the VM
to prevent any data corruption or loss or even leakage.

> I'll keep repeating this, x86_64 exceptions are a trainwreck, and IST in
> specific is utter crap.

I agree, but don't forget the most prominent underlying reason for IST:
The SYSCALL gap. If SYSCALL would switch stacks most of those issues
would not exist. IST would still be needed because there are no task
gates in x86-64, but still...

Regards,

	Joerg


  reply	other threads:[~2020-06-23 12:04 UTC|newest]

Thread overview: 181+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-19  9:12 [RFC PATCH 00/70 v2] x86: SEV-ES Guest Support Joerg Roedel
2020-03-19  9:12 ` [PATCH 01/70] KVM: SVM: Add GHCB definitions Joerg Roedel
2020-03-23 13:23   ` [PATCH] KVM: SVM: Use __packed shorthard Borislav Petkov
2020-03-24 12:43     ` Joerg Roedel
2020-03-19  9:12 ` [PATCH 02/70] KVM: SVM: Add GHCB Accessor functions Joerg Roedel
2020-03-19  9:13 ` [PATCH 03/70] x86/cpufeatures: Add SEV-ES CPU feature Joerg Roedel
2020-03-19  9:13 ` [PATCH 04/70] x86/traps: Move some definitions to <asm/trap_defs.h> Joerg Roedel
2020-03-19  9:13 ` [PATCH 05/70] x86/insn: Make inat-tables.c suitable for pre-decompression code Joerg Roedel
2020-03-25 15:39   ` Borislav Petkov
2020-03-27  3:02     ` Masami Hiramatsu
2020-04-16 15:24       ` Joerg Roedel
2020-04-17 12:50         ` Masami Hiramatsu
2020-04-17 13:39           ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 06/70] x86/umip: Factor out instruction fetch Joerg Roedel
2020-03-26 17:21   ` Borislav Petkov
2020-03-19  9:13 ` [PATCH 07/70] x86/umip: Factor out instruction decoding Joerg Roedel
2020-03-26 17:24   ` Borislav Petkov
2020-03-19  9:13 ` [PATCH 08/70] x86/insn: Add insn_get_modrm_reg_off() Joerg Roedel
2020-03-27  3:57   ` Masami Hiramatsu
2020-03-19  9:13 ` [PATCH 09/70] x86/insn: Add insn_rep_prefix() helper Joerg Roedel
2020-03-27  3:56   ` Masami Hiramatsu
2020-03-19  9:13 ` [PATCH 10/70] x86/boot/compressed: Fix debug_puthex() parameter type Joerg Roedel
2020-03-28 11:23   ` [tip: x86/boot] " tip-bot2 for Joerg Roedel
2020-03-19  9:13 ` [PATCH 11/70] x86/boot/compressed/64: Disable red-zone usage Joerg Roedel
2020-03-31 13:16   ` Borislav Petkov
2020-03-19  9:13 ` [PATCH 12/70] x86/boot/compressed/64: Add IDT Infrastructure Joerg Roedel
2020-04-07  2:21   ` Arvind Sankar
2020-04-16 13:30     ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 13/70] x86/boot/compressed/64: Rename kaslr_64.c to ident_map_64.c Joerg Roedel
2020-03-19  9:13 ` [PATCH 14/70] x86/boot/compressed/64: Add page-fault handler Joerg Roedel
2020-04-02 11:49   ` Borislav Petkov
2020-03-19  9:13 ` [PATCH 15/70] x86/boot/compressed/64: Always switch to own page-table Joerg Roedel
2020-04-06 11:56   ` Borislav Petkov
2020-03-19  9:13 ` [PATCH 16/70] x86/boot/compressed/64: Don't pre-map memory in KASLR code Joerg Roedel
2020-03-19  9:13 ` [PATCH 17/70] x86/boot/compressed/64: Change add_identity_map() to take start and end Joerg Roedel
2020-03-19  9:13 ` [PATCH 18/70] x86/boot/compressed/64: Add stage1 #VC handler Joerg Roedel
2020-03-20 21:16   ` David Rientjes
2020-03-20 22:19     ` Joerg Roedel
2020-04-06 12:41   ` Borislav Petkov
2020-03-19  9:13 ` [PATCH 19/70] x86/boot/compressed/64: Call set_sev_encryption_mask earlier Joerg Roedel
2020-03-19  9:13 ` [PATCH 20/70] x86/boot/compressed/64: Check return value of kernel_ident_mapping_init() Joerg Roedel
2020-03-19  9:13 ` [PATCH 21/70] x86/boot/compressed/64: Add function to map a page unencrypted Joerg Roedel
2020-03-20 20:53   ` David Rientjes
2020-03-20 21:02     ` Dave Hansen
2020-03-20 22:12       ` Joerg Roedel
2020-03-20 22:26         ` Dave Hansen
2020-03-21 15:40           ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 22/70] x86/boot/compressed/64: Setup GHCB Based VC Exception handler Joerg Roedel
2020-03-19  9:13 ` [PATCH 23/70] x86/sev-es: Add support for handling IOIO exceptions Joerg Roedel
2020-03-20 21:03   ` David Rientjes
2020-03-20 22:24     ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 24/70] x86/fpu: Move xgetbv()/xsetbv() into separate header Joerg Roedel
2020-03-19  9:13 ` [PATCH 25/70] x86/sev-es: Add CPUID handling to #VC handler Joerg Roedel
2020-03-19  9:13 ` [PATCH 26/70] x86/idt: Move IDT to data segment Joerg Roedel
2020-03-19  9:13 ` [PATCH 27/70] x86/idt: Split idt_data setup out of set_intr_gate() Joerg Roedel
2020-03-19  9:13 ` [PATCH 28/70] x86/idt: Move two function from k/idt.c to i/a/desc.h Joerg Roedel
2020-03-19  9:13 ` [PATCH 29/70] x86/head/64: Install boot GDT Joerg Roedel
2020-03-19  9:13 ` [PATCH 30/70] x86/head/64: Reload GDT after switch to virtual addresses Joerg Roedel
2020-03-19  9:13 ` [PATCH 31/70] x86/head/64: Load segment registers earlier Joerg Roedel
2020-03-19  9:13 ` [PATCH 32/70] x86/head/64: Switch to initial stack earlier Joerg Roedel
2020-03-19  9:13 ` [PATCH 33/70] x86/head/64: Build k/head64.c with -fno-stack-protector Joerg Roedel
2020-03-19  9:13 ` [PATCH 34/70] x86/head/64: Load IDT earlier Joerg Roedel
2020-03-19  9:13 ` [PATCH 35/70] x86/head/64: Move early exception dispatch to C code Joerg Roedel
2020-03-19  9:13 ` [PATCH 36/70] x86/sev-es: Add SEV-ES Feature Detection Joerg Roedel
2020-03-19  9:13 ` [PATCH 37/70] x86/sev-es: Compile early handler code into kernel image Joerg Roedel
2020-03-19  9:13 ` [PATCH 38/70] x86/sev-es: Setup early #VC handler Joerg Roedel
2020-03-19  9:13 ` [PATCH 39/70] x86/sev-es: Setup GHCB based boot " Joerg Roedel
2020-03-19  9:13 ` [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime handler Joerg Roedel
2020-04-14 19:03   ` Mike Stunes
2020-04-14 20:04     ` Tom Lendacky
2020-04-14 20:12       ` Dave Hansen
2020-04-14 20:16         ` Tom Lendacky
2020-04-14 20:18           ` Tom Lendacky
2020-04-15 15:54       ` Joerg Roedel
2020-04-15 15:53     ` Joerg Roedel
2020-04-23  1:33       ` Bo Gan
2020-04-23 11:30         ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 41/70] x86/sev-es: Add Runtime #VC Exception Handler Joerg Roedel
2020-03-19 15:44   ` Andy Lutomirski
2020-03-19 16:24     ` Joerg Roedel
2020-03-19 18:43       ` Andy Lutomirski
2020-03-19 19:38         ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 42/70] x86/sev-es: Support nested #VC exceptions Joerg Roedel
2020-03-19 15:46   ` Andy Lutomirski
2020-03-19 16:12     ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 43/70] x86/sev-es: Wire up existing #VC exit-code handlers Joerg Roedel
2020-03-19  9:13 ` [PATCH 44/70] x86/sev-es: Handle instruction fetches from user-space Joerg Roedel
2020-03-19  9:13 ` [PATCH 45/70] x86/sev-es: Harden runtime #VC handler for exceptions " Joerg Roedel
2020-03-19  9:13 ` [PATCH 46/70] x86/sev-es: Filter exceptions not supported " Joerg Roedel
2020-03-19  9:13 ` [PATCH 47/70] x86/sev-es: Handle MMIO events Joerg Roedel
2020-03-19  9:13 ` [PATCH 48/70] x86/sev-es: Handle MMIO String Instructions Joerg Roedel
2020-03-19  9:13 ` [PATCH 49/70] x86/sev-es: Handle MSR events Joerg Roedel
2020-03-19  9:13 ` [PATCH 50/70] x86/sev-es: Handle DR7 read/write events Joerg Roedel
2020-03-19  9:13 ` [PATCH 51/70] x86/sev-es: Handle WBINVD Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 52/70] x86/sev-es: Handle RDTSC Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 53/70] x86/sev-es: Handle RDPMC Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 54/70] x86/sev-es: Handle INVD Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 55/70] x86/sev-es: Handle RDTSCP Events Joerg Roedel
2020-04-24 21:03   ` [PATCH] Allow RDTSC and RDTSCP from userspace Mike Stunes
2020-04-24 21:24     ` Dave Hansen
2020-04-24 21:27       ` Tom Lendacky
2020-04-24 22:53         ` Dave Hansen
2020-04-25 12:49           ` Joerg Roedel
2020-04-25 18:15             ` Andy Lutomirski
2020-04-25 19:10               ` Joerg Roedel
2020-04-25 19:47                 ` Andy Lutomirski
2020-04-25 20:23                   ` Joerg Roedel
2020-04-25 22:10                     ` Andy Lutomirski
2020-04-27 17:37                       ` Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace) Andy Lutomirski
2020-04-27 18:15                         ` Andrew Cooper
2020-04-27 18:43                         ` Tom Lendacky
2020-04-28  7:55                         ` Joerg Roedel
2020-04-28 16:34                           ` Andrew Cooper
2020-06-23 11:07                           ` Peter Zijlstra
2020-06-23 11:30                             ` Joerg Roedel
2020-06-23 11:48                               ` Peter Zijlstra
2020-06-23 12:04                                 ` Joerg Roedel [this message]
2020-06-23 12:52                                   ` Peter Zijlstra
2020-06-23 13:40                                     ` Joerg Roedel
2020-06-23 13:59                                       ` Peter Zijlstra
2020-06-23 14:53                                         ` Peter Zijlstra
2020-06-23 14:59                                           ` Joerg Roedel
2020-06-23 15:23                                             ` Peter Zijlstra
2020-06-23 15:38                                               ` Peter Zijlstra
2020-06-23 15:38                                               ` Joerg Roedel
2020-06-23 16:02                                                 ` Peter Zijlstra
2020-06-23 15:39                                               ` Andrew Cooper
2020-06-23 15:52                                                 ` Peter Zijlstra
2020-06-23 16:03                                                   ` Dave Hansen
2020-06-23 16:13                                                     ` Peter Zijlstra
2020-06-23 16:13                                                 ` Borislav Petkov
2020-06-23 11:51                               ` Andrew Cooper
2020-06-23 12:47                                 ` Peter Zijlstra
2020-06-23 13:57                                   ` Andrew Cooper
2020-06-23 15:51                                 ` Borislav Petkov
2020-06-23  9:45                         ` Joerg Roedel
2020-06-23 10:45                           ` Peter Zijlstra
2020-06-23 11:11                             ` Joerg Roedel
2020-06-23 11:14                               ` Peter Zijlstra
2020-06-23 11:43                                 ` Joerg Roedel
2020-06-23 11:50                                   ` Peter Zijlstra
2020-06-23 12:12                                     ` Joerg Roedel
2020-06-23 13:03                                       ` Peter Zijlstra
2020-06-23 14:49                                         ` Joerg Roedel
2020-06-23 15:16                                           ` Peter Zijlstra
2020-06-23 15:32                                             ` Andrew Cooper
2020-06-23 16:10                                               ` Borislav Petkov
2020-06-23 15:22                                         ` Andrew Cooper
2020-06-23 18:26                                           ` Andy Lutomirski
2020-06-23 18:56                                             ` Andrew Cooper
2020-04-27 18:47             ` [PATCH] Allow RDTSC and RDTSCP from userspace Dave Hansen
2020-04-25 12:28     ` Joerg Roedel
2020-03-19  9:13 ` [PATCH 56/70] x86/sev-es: Handle MONITOR/MONITORX Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 57/70] x86/sev-es: Handle MWAIT/MWAITX Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 58/70] x86/sev-es: Handle VMMCALL Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 59/70] x86/sev-es: Handle #AC Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 60/70] x86/sev-es: Handle #DB Events Joerg Roedel
2020-03-19  9:13 ` [PATCH 61/70] x86/paravirt: Allow hypervisor specific VMMCALL handling under SEV-ES Joerg Roedel
2020-03-19  9:13 ` [PATCH 62/70] x86/kvm: Add KVM " Joerg Roedel
2020-03-20 21:23   ` David Rientjes
2020-03-20 22:21     ` Joerg Roedel
2020-03-19  9:14 ` [PATCH 63/70] x86/vmware: Add VMware specific handling for VMMCALL " Joerg Roedel
2020-03-19 10:18   ` Thomas Hellstrom
2020-03-19  9:14 ` [PATCH 64/70] x86/realmode: Add SEV-ES specific trampoline entry point Joerg Roedel
2020-03-19  9:14 ` [PATCH 65/70] x86/realmode: Setup AP jump table Joerg Roedel
2020-03-19  9:14 ` [PATCH 66/70] x86/head/64: Don't call verify_cpu() on starting APs Joerg Roedel
2020-03-19  9:14 ` [PATCH 67/70] x86/head/64: Rename start_cpu0 Joerg Roedel
2020-03-19  9:14 ` [PATCH 68/70] x86/sev-es: Support CPU offline/online Joerg Roedel
2020-03-19  9:14 ` [PATCH 69/70] x86/cpufeature: Add SEV_ES_GUEST CPU Feature Joerg Roedel
2020-03-19  9:14 ` [PATCH 70/70] x86/sev-es: Add NMI state tracking Joerg Roedel
2020-03-19 15:35   ` Andy Lutomirski
2020-03-19 16:07     ` Joerg Roedel
2020-03-19 18:40       ` Andy Lutomirski
2020-03-19 19:26         ` Joerg Roedel
2020-03-19 21:27           ` Andy Lutomirski
2020-03-20 19:48             ` Joerg Roedel
2020-03-20 13:17     ` [RFC PATCH v2.1] x86/sev-es: Handle NMI State Joerg Roedel
2020-03-20 14:42       ` Dave Hansen
2020-03-20 19:42         ` Joerg Roedel
2020-03-19 16:53   ` [PATCH 70/70] x86/sev-es: Add NMI state tracking Mika Penttilä
2020-03-19 19:41     ` Joerg Roedel

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