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Date: Thu, 25 Aug 2022 14:09:26 -0600
From: Peter Gonda <pgonda@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: Dionna Amalie Glaze <dionnaglaze@...gle.com>,
Brijesh Singh <brijesh.singh@....com>,
"the arch/x86 maintainers" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
"open list:X86 KVM CPUs" <kvm@...r.kernel.org>,
linux-efi <linux-efi@...r.kernel.org>,
platform-driver-x86@...r.kernel.org, linux-coco@...ts.linux.dev,
Linux Memory Management List <linux-mm@...ck.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
"H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Sergio Lopez <slp@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
David Rientjes <rientjes@...gle.com>,
Dov Murik <dovmurik@...ux.ibm.com>,
Tobin Feldman-Fitzthum <tobin@....com>,
Borislav Petkov <bp@...en8.de>,
Michael Roth <michael.roth@....com>,
Vlastimil Babka <vbabka@...e.cz>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Andi Kleen <ak@...ux.intel.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
brijesh.ksingh@...il.com, Tony Luck <tony.luck@...el.com>,
Marc Orr <marcorr@...gle.com>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v12 43/46] virt: Add SEV-SNP guest driver
On Thu, Aug 25, 2022 at 12:54 PM Tom Lendacky <thomas.lendacky@....com> wrote:
>
> On 8/24/22 14:28, Peter Gonda wrote:
> > On Wed, Aug 24, 2022 at 12:01 PM Dionna Amalie Glaze
> > <dionnaglaze@...gle.com> wrote:
> >>
> >> Apologies for the necropost, but I noticed strange behavior testing my
> >> own Golang-based wrapper around the /dev/sev-guest driver.
> >>
> >>> +
> >>> +static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
> >>> + u8 type, void *req_buf, size_t req_sz, void *resp_buf,
> >>> + u32 resp_sz, __u64 *fw_err)
> >>> +{
> >>> + unsigned long err;
> >>> + u64 seqno;
> >>> + int rc;
> >>> +
> >>> + /* Get message sequence and verify that its a non-zero */
> >>> + seqno = snp_get_msg_seqno(snp_dev);
> >>> + if (!seqno)
> >>> + return -EIO;
> >>> +
> >>> + memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
> >>> +
> >>> + /* Encrypt the userspace provided payload */
> >>> + rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
> >>> + if (rc)
> >>> + return rc;
> >>> +
> >>> + /* Call firmware to process the request */
> >>> + rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
> >>> + if (fw_err)
> >>> + *fw_err = err;
> >>> +
> >>> + if (rc)
> >>> + return rc;
> >>> +
> >>
> >> The fw_err is written back regardless of rc, so since err is
> >> uninitialized, you can end up with garbage written back. I've worked
> >> around this by only caring about fw_err when the result is -EIO, but
> >> thought that I should bring this up.
> >
> > I also noticed that we use a u64 in snp_guest_request_ioctl.fw_err and
> > u32 in sev_issue_cmd.error when these should be errors from the
> > sev_ret_code enum IIUC.
>
> The reason for the u64 is that the Extended Guest Request can return a
> firmware error or a hypervisor error. To distinguish between the two, a
> firmware error is contained in the lower 32-bits, while a hypervisor error
> is contained in the upper 32-bits (e.g. when not enough contiguous pages
> of memory have been supplied).
Ah, makes sense. I was trying to think of a way to codify the state
described above where we error so early in the IOCTL or call that the
PSP is never called, something like below. I think using UINT32_MAX
still works with how u64 of Extended Guest Request is spec'd. Is this
interesting to clean up the PSP driver and internal calls, and the new
sev-guest driver?
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 63dc626627a0..d1e605567d5e 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -22,6 +22,7 @@
#include <linux/efi.h>
#include <linux/platform_device.h>
#include <linux/io.h>
+#include <linux/psp-sev.h>
#include <asm/cpu_entry_area.h>
#include <asm/stacktrace.h>
@@ -2177,6 +2178,8 @@ int snp_issue_guest_request(u64 exit_code,
struct snp_req_data *input, unsigned
if (!fw_err)
return -EINVAL;
+ fw_err = SEV_RET_NO_FW_CALL;
+
/*
* __sev_get_ghcb() needs to run with IRQs disabled because it is using
* a per-CPU GHCB.
@@ -2209,6 +2212,8 @@ int snp_issue_guest_request(u64 exit_code,
struct snp_req_data *input, unsigned
*fw_err = ghcb->save.sw_exit_info_2;
ret = -EIO;
+ } else {
+ *fw_err = 0;
}
e_put:
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 9f588c9728f8..e71d6e39aa2b 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -439,7 +439,7 @@ static int __sev_platform_init_locked(int *error)
{
struct psp_device *psp = psp_master;
struct sev_device *sev;
- int rc, psp_ret = -1;
+ int rc, psp_ret = SEV_RET_NO_FW_CALL;
int (*init_function)(int *error);
if (!psp || !psp->sev_data)
diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
index 91b4c63d5cbf..b8f2c129d63d 100644
--- a/include/uapi/linux/psp-sev.h
+++ b/include/uapi/linux/psp-sev.h
@@ -36,6 +36,11 @@ enum {
* SEV Firmware status code
*/
...skipping...
#include <asm/cpu_entry_area.h>
#include <asm/stacktrace.h>
@@ -2177,6 +2178,8 @@ int snp_issue_guest_request(u64 exit_code,
struct snp_req_data *input, unsigned
if (!fw_err)
return -EINVAL;
+ fw_err = SEV_RET_NO_FW_CALL;
+
/*
* __sev_get_ghcb() needs to run with IRQs disabled because it is using
* a per-CPU GHCB.
@@ -2209,6 +2212,8 @@ int snp_issue_guest_request(u64 exit_code,
struct snp_req_data *input, unsigned
*fw_err = ghcb->save.sw_exit_info_2;
ret = -EIO;
+ } else {
+ *fw_err = 0;
}
e_put:
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 9f588c9728f8..e71d6e39aa2b 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -439,7 +439,7 @@ static int __sev_platform_init_locked(int *error)
{
struct psp_device *psp = psp_master;
struct sev_device *sev;
- int rc, psp_ret = -1;
+ int rc, psp_ret = SEV_RET_NO_FW_CALL;
int (*init_function)(int *error);
if (!psp || !psp->sev_data)
diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
index 91b4c63d5cbf..b8f2c129d63d 100644
--- a/include/uapi/linux/psp-sev.h
+++ b/include/uapi/linux/psp-sev.h
@@ -36,6 +36,11 @@ enum {
* SEV Firmware status code
*/
typedef enum {
+ /*
+ * This error code is not in the SEV spec but is added to convey that
+ * there was an error that prevented the SEV Firmware from being called.
+ */
+ SEV_RET_NO_FW_CALL = -1,
SEV_RET_SUCCESS = 0,
SEV_RET_INVALID_PLATFORM_STATE,
SEV_RET_INVALID_GUEST_STATE,
> >
> >>
> >> --
> >> -Dionna Glaze, PhD (she/her)
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