From: Peter Gonda <pgonda@google.com>
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
kvm list <kvm@vger.kernel.org>,
linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
linux-coco@lists.linux.dev, linux-mm@kvack.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
Tom Lendacky <thomas.lendacky@amd.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Ard Biesheuvel <ardb@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Sergio Lopez <slp@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Dov Murik <dovmurik@linux.ibm.com>,
Tobin Feldman-Fitzthum <tobin@ibm.com>,
Borislav Petkov <bp@alien8.de>,
Michael Roth <michael.roth@amd.com>,
Vlastimil Babka <vbabka@suse.cz>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Andi Kleen <ak@linux.intel.com>,
tony.luck@intel.com, Marc Orr <marcorr@google.com>,
sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH Part1 v5 34/38] x86/sev: Add snp_msg_seqno() helper
Date: Thu, 9 Sep 2021 09:43:46 -0600 [thread overview]
Message-ID: <CAMkAt6pT4vkgLxTN1Lj54ufaStyCHHitNaHAdZvEgDV8Nyrx-Q@mail.gmail.com> (raw)
In-Reply-To: <4742dbfe-4e02-a7e3-6464-905ccc602e6c@amd.com>
)()
On Thu, Sep 9, 2021 at 9:26 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
>
>
> On 9/9/21 9:54 AM, Peter Gonda wrote:
> > On Fri, Aug 20, 2021 at 9:22 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
> >>
> >> The SNP guest request message header contains a message count. The
> >> message count is used while building the IV. The PSP firmware increments
> >> the message count by 1, and expects that next message will be using the
> >> incremented count. The snp_msg_seqno() helper will be used by driver to
> >> get the message sequence counter used in the request message header,
> >> and it will be automatically incremented after the request is successful.
> >> The incremented value is saved in the secrets page so that the kexec'ed
> >> kernel knows from where to begin.
> >>
> >> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> >> ---
> >> arch/x86/kernel/sev.c | 79 +++++++++++++++++++++++++++++++++++++++
> >> include/linux/sev-guest.h | 37 ++++++++++++++++++
> >> 2 files changed, 116 insertions(+)
> >>
> >> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> >> index 319a40fc57ce..f42cd5a8e7bb 100644
> >> --- a/arch/x86/kernel/sev.c
> >> +++ b/arch/x86/kernel/sev.c
> >> @@ -51,6 +51,8 @@ static struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
> >> */
> >> static struct ghcb __initdata *boot_ghcb;
> >>
> >> +static u64 snp_secrets_phys;
> >> +
> >> /* #VC handler runtime per-CPU data */
> >> struct sev_es_runtime_data {
> >> struct ghcb ghcb_page;
> >> @@ -2030,6 +2032,80 @@ bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
> >> halt();
> >> }
> >>
> >> +static struct snp_secrets_page_layout *snp_map_secrets_page(void)
> >> +{
> >> + u16 __iomem *secrets;
> >> +
> >> + if (!snp_secrets_phys || !sev_feature_enabled(SEV_SNP))
> >> + return NULL;
> >> +
> >> + secrets = ioremap_encrypted(snp_secrets_phys, PAGE_SIZE);
> >> + if (!secrets)
> >> + return NULL;
> >> +
> >> + return (struct snp_secrets_page_layout *)secrets;
> >> +}
> >> +
> >> +static inline u64 snp_read_msg_seqno(void)
> >> +{
> >> + struct snp_secrets_page_layout *layout;
> >> + u64 count;
> >> +
> >> + layout = snp_map_secrets_page();
> >> + if (!layout)
> >> + return 0;
> >> +
> >> + /* Read the current message sequence counter from secrets pages */
> >> + count = readl(&layout->os_area.msg_seqno_0);
> >> +
> >> + iounmap(layout);
> >> +
> >> + /* The sequence counter must begin with 1 */
> >> + if (!count)
> >> + return 1;
> >> +
> >> + return count + 1;
> >> +}
> >> +
> >> +u64 snp_msg_seqno(void)
> >> +{
> >> + u64 count = snp_read_msg_seqno();
> >> +
> >> + if (unlikely(!count))
> >> + return 0;
> >> +
> >> + /*
> >> + * The message sequence counter for the SNP guest request is a
> >> + * 64-bit value but the version 2 of GHCB specification defines a
> >> + * 32-bit storage for the it.
> >> + */
> >> + if (count >= UINT_MAX)
> >> + return 0;
> >> +
> >> + return count;
> >> +}
> >> +EXPORT_SYMBOL_GPL(snp_msg_seqno);
> >
> > Do we need some sort of get sequence number, then ack that sequence
> > number was used API? Taking your host changes in Part2 V5 as an
> > example. If 'snp_setup_guest_buf' fails the given sequence number is
> > never actually used by a message to the PSP. So the guest will have
> > the wrong current sequence number, an off by 1 error, right?
> >
>
> The sequence number should be incremented only after the command is
> successful. In this particular case the next caller should not get the
> updated sequence number.
>
> Having said so, there is a bug in current code that will cause us to
> increment the sequence number on failure. I notice it last week and have
> it fixed in v6 wip branch.
>
> int snp_issue_guest_request(....)
> {
>
> .....
> .....
>
> ret = sev_es_ghcb_hv_call(ghcb, NULL, id, input->req_gpa, input->resp_gpa);
> if (ret)
> goto e_put;
>
> if (ghcb->save.sw_exit_info_2) {
> ...
> ...
>
> ret = -EIO;
> goto e_put; /** THIS WAS MISSING */
> }
>
> /* The command was successful, increment the sequence counter. */
> snp_gen_msg_seqno();
> e_put:
> ....
> }
>
> Does this address your concern?
So the 'snp_msg_seqno()' call in 'enc_payload' will not increment the
counter, its only incremented on 'snp_gen_msg_seqno()'? If thats
correct, that addresses my first concern.
>
>
> > Also it seems like there is a concurrency error waiting to happen
> > here. If 2 callers call snp_msg_seqno() before either actually places
> > a call to the PSP, if the first caller's request doesn't reach the PSP
> > before the second caller's request both calls will fail. And again I
> > think the sequence numbers in the guest will be incorrect and
> > unrecoverable.
> >
>
> So far, the only user for the snp_msg_seqno() is the attestation driver.
> And the driver is designed to serialize the vmgexit request and thus we
> should not run into concurrence issue.
That seems a little dangerous as any module new code or out-of-tree
module could use this function thus revealing this race condition
right? Could we at least have a comment on these functions
(snp_msg_seqno and snp_gen_msg_seqno) noting this?
>
> >> +
> >> +static void snp_gen_msg_seqno(void)
> >> +{
> >> + struct snp_secrets_page_layout *layout;
> >> + u64 count;
> >> +
> >> + layout = snp_map_secrets_page();
> >> + if (!layout)
> >> + return;
> >> +
> >> + /*
> >> + * The counter is also incremented by the PSP, so increment it by 2
> >> + * and save in secrets page.
> >> + */
> >> + count = readl(&layout->os_area.msg_seqno_0);
> >> + count += 2;
> >> +
> >> + writel(count, &layout->os_area.msg_seqno_0);
> >> + iounmap(layout);
> >> +}
> >> +
> >> int snp_issue_guest_request(int type, struct snp_guest_request_data *input, unsigned long *fw_err)
> >> {
> >> struct ghcb_state state;
> >> @@ -2077,6 +2153,9 @@ int snp_issue_guest_request(int type, struct snp_guest_request_data *input, unsi
> >> ret = -EIO;
> >> }
> >>
> >> + /* The command was successful, increment the sequence counter */
> >> + snp_gen_msg_seqno();
> >> +
> >> e_put:
> >> __sev_put_ghcb(&state);
> >> e_restore_irq:
> >> diff --git a/include/linux/sev-guest.h b/include/linux/sev-guest.h
> >> index 24dd17507789..16b6af24fda7 100644
> >> --- a/include/linux/sev-guest.h
> >> +++ b/include/linux/sev-guest.h
> >> @@ -20,6 +20,41 @@ enum vmgexit_type {
> >> GUEST_REQUEST_MAX
> >> };
> >>
> >> +/*
> >> + * The secrets page contains 96-bytes of reserved field that can be used by
> >> + * the guest OS. The guest OS uses the area to save the message sequence
> >> + * number for each VMPCK.
> >> + *
> >> + * See the GHCB spec section Secret page layout for the format for this area.
> >> + */
> >> +struct secrets_os_area {
> >> + u32 msg_seqno_0;
> >> + u32 msg_seqno_1;
> >> + u32 msg_seqno_2;
> >> + u32 msg_seqno_3;
> >> + u64 ap_jump_table_pa;
> >> + u8 rsvd[40];
> >> + u8 guest_usage[32];
> >> +} __packed;
> >> +
> >> +#define VMPCK_KEY_LEN 32
> >> +
> >> +/* See the SNP spec for secrets page format */
> >> +struct snp_secrets_page_layout {
> >> + u32 version;
> >> + u32 imien : 1,
> >> + rsvd1 : 31;
> >> + u32 fms;
> >> + u32 rsvd2;
> >> + u8 gosvw[16];
> >> + u8 vmpck0[VMPCK_KEY_LEN];
> >> + u8 vmpck1[VMPCK_KEY_LEN];
> >> + u8 vmpck2[VMPCK_KEY_LEN];
> >> + u8 vmpck3[VMPCK_KEY_LEN];
> >> + struct secrets_os_area os_area;
> >> + u8 rsvd3[3840];
> >> +} __packed;
> >> +
> >> /*
> >> * The error code when the data_npages is too small. The error code
> >> * is defined in the GHCB specification.
> >> @@ -36,6 +71,7 @@ struct snp_guest_request_data {
> >> #ifdef CONFIG_AMD_MEM_ENCRYPT
> >> int snp_issue_guest_request(int vmgexit_type, struct snp_guest_request_data *input,
> >> unsigned long *fw_err);
> >> +u64 snp_msg_seqno(void);
> >> #else
> >>
> >> static inline int snp_issue_guest_request(int type, struct snp_guest_request_data *input,
> >> @@ -43,6 +79,7 @@ static inline int snp_issue_guest_request(int type, struct snp_guest_request_dat
> >> {
> >> return -ENODEV;
> >> }
> >> +static inline u64 snp_msg_seqno(void) { return 0; }
> >>
> >> #endif /* CONFIG_AMD_MEM_ENCRYPT */
> >> #endif /* __LINUX_SEV_GUEST_H__ */
> >> --
> >> 2.17.1
> >>
> >>
next prev parent reply other threads:[~2021-09-09 15:44 UTC|newest]
Thread overview: 123+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-20 15:18 [PATCH Part1 v5 00/38] Add AMD Secure Nested Paging (SEV-SNP) Guest Support Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 01/38] x86/mm: Add sev_feature_enabled() helper Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 02/38] x86/sev: Shorten GHCB terminate macro names Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 03/38] x86/sev: Get rid of excessive use of defines Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 04/38] x86/head64: Carve out the guest encryption postprocessing into a helper Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 05/38] x86/sev: Define the Linux specific guest termination reasons Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 06/38] x86/sev: Save the negotiated GHCB version Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 07/38] x86/sev: Add support for hypervisor feature VMGEXIT Brijesh Singh
2021-08-23 9:47 ` Borislav Petkov
2021-08-23 18:25 ` Brijesh Singh
2021-08-23 18:34 ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 08/38] x86/sev: Check SEV-SNP features support Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 09/38] x86/sev: Add a helper for the PVALIDATE instruction Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 10/38] x86/sev: Check the vmpl level Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 11/38] x86/compressed: Add helper for validating pages in the decompression stage Brijesh Singh
2021-08-23 14:16 ` Borislav Petkov
2021-08-23 18:55 ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 12/38] x86/compressed: Register GHCB memory when SEV-SNP is active Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 13/38] x86/sev: " Brijesh Singh
2021-08-23 17:35 ` Borislav Petkov
2021-08-23 18:56 ` Brijesh Singh
2021-08-23 19:45 ` [PATCH] x86/sev: Remove do_early_exception() forward declarations Borislav Petkov
2021-08-23 20:06 ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 14/38] x86/sev: Add helper for validating pages in early enc attribute changes Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 15/38] x86/kernel: Make the bss.decrypted section shared in RMP table Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 16/38] x86/kernel: Validate rom memory before accessing when SEV-SNP is active Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 17/38] x86/mm: Add support to validate memory when changing C-bit Brijesh Singh
2021-08-25 11:06 ` Borislav Petkov
2021-08-25 13:54 ` Brijesh Singh
2021-08-25 14:00 ` Borislav Petkov
2021-08-27 17:09 ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 18/38] KVM: SVM: Define sev_features and vmpl field in the VMSA Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 19/38] KVM: SVM: Create a separate mapping for the SEV-ES save area Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 20/38] KVM: SVM: Create a separate mapping for the GHCB " Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 21/38] KVM: SVM: Update the SEV-ES save area mapping Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 22/38] x86/sev: Use SEV-SNP AP creation to start secondary CPUs Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 23/38] x86/head/64: set up a startup %gs for stack protector Brijesh Singh
2021-08-25 14:29 ` Borislav Petkov
2021-08-25 15:18 ` Michael Roth
2021-08-25 16:29 ` Borislav Petkov
2021-08-27 13:38 ` Michael Roth
2021-08-31 8:03 ` Borislav Petkov
2021-08-31 23:30 ` Michael Roth
2021-08-25 15:07 ` Joerg Roedel
2021-08-25 17:07 ` Michael Roth
2021-08-20 15:19 ` [PATCH Part1 v5 24/38] x86/sev: move MSR-based VMGEXITs for CPUID to helper Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 25/38] KVM: x86: move lookup of indexed CPUID leafs " Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 26/38] x86/compressed/acpi: move EFI config table access to common code Brijesh Singh
2021-08-25 15:18 ` Borislav Petkov
2021-08-25 17:14 ` Michael Roth
2021-08-20 15:19 ` [PATCH Part1 v5 27/38] x86/boot: Add Confidential Computing type to setup_data Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 28/38] x86/compressed/64: enable SEV-SNP-validated CPUID in #VC handler Brijesh Singh
2021-08-25 19:19 ` Borislav Petkov
2021-08-27 16:46 ` Michael Roth
2021-08-31 10:04 ` Borislav Petkov
2021-09-01 1:03 ` Michael Roth
2021-09-02 10:53 ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 29/38] x86/boot: add a pointer to Confidential Computing blob in bootparams Brijesh Singh
2021-08-27 13:51 ` Borislav Petkov
2021-08-27 18:48 ` Michael Roth
2021-08-20 15:19 ` [PATCH Part1 v5 30/38] x86/compressed/64: store Confidential Computing blob address " Brijesh Singh
2021-08-27 14:15 ` Borislav Petkov
2021-08-27 19:09 ` Michael Roth
2021-08-31 10:26 ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 31/38] x86/compressed/64: add identity mapping for Confidential Computing blob Brijesh Singh
2021-08-27 14:43 ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 32/38] x86/sev: enable SEV-SNP-validated CPUID in #VC handlers Brijesh Singh
2021-08-27 15:18 ` Borislav Petkov
2021-08-27 15:47 ` Brijesh Singh
2021-08-27 16:56 ` Borislav Petkov
2021-08-27 18:39 ` Michael Roth
2021-08-27 18:32 ` Michael Roth
2021-08-30 16:03 ` Michael Roth
2021-08-31 16:22 ` Borislav Petkov
2021-09-01 1:16 ` Michael Roth
2021-09-02 11:05 ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 33/38] x86/sev: Provide support for SNP guest request NAEs Brijesh Singh
2021-08-27 17:44 ` Borislav Petkov
2021-08-27 18:07 ` Brijesh Singh
2021-08-27 18:13 ` Borislav Petkov
2021-08-27 18:27 ` Brijesh Singh
2021-08-27 18:38 ` Borislav Petkov
2021-08-27 19:57 ` Tom Lendacky
2021-08-27 20:17 ` Borislav Petkov
2021-08-27 20:31 ` Tom Lendacky
2021-08-20 15:19 ` [PATCH Part1 v5 34/38] x86/sev: Add snp_msg_seqno() helper Brijesh Singh
2021-08-27 18:41 ` Borislav Petkov
2021-08-30 15:07 ` Brijesh Singh
2021-09-02 11:26 ` Borislav Petkov
2021-09-02 15:27 ` Brijesh Singh
2021-08-31 20:46 ` Dov Murik
2021-08-31 21:13 ` Brijesh Singh
2021-09-09 14:54 ` Peter Gonda
2021-09-09 15:26 ` Brijesh Singh
2021-09-09 15:43 ` Peter Gonda [this message]
2021-09-09 16:17 ` Brijesh Singh
2021-09-09 16:21 ` Peter Gonda
2021-09-09 19:26 ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 35/38] x86/sev: Register SNP guest request platform device Brijesh Singh
2021-08-31 11:37 ` Dov Murik
2021-08-31 16:03 ` Brijesh Singh
2021-09-02 16:40 ` Borislav Petkov
2021-09-02 19:58 ` Brijesh Singh
2021-09-03 8:15 ` Dov Murik
2021-09-03 12:08 ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 36/38] virt: Add SEV-SNP guest driver Brijesh Singh
2021-09-06 17:38 ` Borislav Petkov
2021-09-07 13:35 ` Brijesh Singh
2021-09-08 13:44 ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 37/38] virt: sevguest: Add support to derive key Brijesh Singh
2021-08-31 18:59 ` Dov Murik
2021-08-31 21:04 ` Brijesh Singh
2021-09-01 5:33 ` Dov Murik
2021-09-08 14:00 ` Borislav Petkov
2021-09-08 21:44 ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 38/38] virt: sevguest: Add support to get extended report Brijesh Singh
2021-08-31 20:22 ` Dov Murik
2021-08-31 21:11 ` Brijesh Singh
2021-09-01 8:32 ` Dov Murik
2021-09-08 17:53 ` Borislav Petkov
2021-09-15 11:46 ` Brijesh Singh
2021-09-15 10:02 ` Dr. David Alan Gilbert
2021-09-15 11:53 ` Brijesh Singh
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