From: Joerg Roedel <joro@8bytes.org>
To: Sean Christopherson <seanjc@google.com>
Cc: x86@kernel.org, Hyunwook Baek <baekhw@google.com>,
Joerg Roedel <jroedel@suse.de>,
stable@vger.kernel.org, hpa@zytor.com,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
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>,
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 2/6] x86/sev-es: Forward page-faults which happen during emulation
Date: Wed, 19 May 2021 15:16:38 +0200 [thread overview]
Message-ID: <YKUPtrquQyImL3h5@8bytes.org> (raw)
In-Reply-To: <YJwQ1xsiDtv3LkBe@google.com>
Hi Sean,
On Wed, May 12, 2021 at 05:31:03PM +0000, Sean Christopherson wrote:
> This got me looking at the flows that "inject" #PF, and I'm pretty sure there
> are bugs in __vc_decode_user_insn() + insn_get_effective_ip().
>
> Problem #1: __vc_decode_user_insn() assumes a #PF if insn_fetch_from_user_inatomic()
> fails, but the majority of failure cases in insn_get_seg_base() are #GPs, not #PF.
>
> res = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
> if (!res) {
> ctxt->fi.vector = X86_TRAP_PF;
> ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
> ctxt->fi.cr2 = ctxt->regs->ip;
> return ES_EXCEPTION;
> }
>
> Problem #2: Using '0' as an error code means a legitimate effective IP of '0'
> will be misinterpreted as a failure. Practically speaking, I highly doubt anyone
> will ever actually run code at address 0, but it's technically possible. The
> most robust approach would be to pass a pointer to @ip and return an actual error
> code. Using a non-canonical magic value might also work, but that could run afoul
> of future shenanigans like LAM.
>
> ip = insn_get_effective_ip(regs);
> if (!ip)
> return 0;
Your observations are all correct. I put some changes onto this
patch-set to fix these problems.
Regards,
Joerg
next prev parent reply other threads:[~2021-05-19 13:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 7:54 [PATCH 0/6] x86/sev-es: Fixes for SEV-ES guest support Joerg Roedel
2021-05-12 7:54 ` [PATCH 1/6] x86/sev-es: Don't return NULL from sev_es_get_ghcb() Joerg Roedel
2021-05-12 7:54 ` [PATCH 2/6] x86/sev-es: Forward page-faults which happen during emulation Joerg Roedel
2021-05-12 17:31 ` Sean Christopherson
2021-05-19 13:16 ` Joerg Roedel [this message]
2021-05-12 7:54 ` [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user Joerg Roedel
2021-05-12 8:04 ` David Laight
2021-05-12 8:16 ` Juergen Gross
2021-05-12 8:50 ` 'Joerg Roedel'
2021-05-12 8:58 ` Juergen Gross
2021-05-12 9:31 ` David Laight
2021-05-12 9:32 ` Joerg Roedel
2021-05-19 11:33 ` 'Joerg Roedel'
2021-05-12 8:37 ` 'Joerg Roedel'
2021-05-12 15:59 ` Dave Hansen
2021-05-12 15:57 ` Dave Hansen
2021-05-12 16:00 ` Joerg Roedel
2021-05-12 7:54 ` [PATCH 4/6] Revert "x86/sev-es: Handle string port IO to kernel memory properly" Joerg Roedel
2021-05-12 17:38 ` Sean Christopherson
2021-05-19 12:22 ` Joerg Roedel
2021-05-12 7:54 ` [PATCH 5/6] x86/sev-es: Fix error message in runtime #VC handler Joerg Roedel
2021-05-12 7:54 ` [PATCH 6/6] x86/sev-es: Leave NMI-mode before sending signals Joerg Roedel
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